Adding Freon to Car AC – Gauge Readings Explained

7:29 am Air Conditioning, DIY, How To Auto Repair

Get your A/C checked at a local shop or check it yourself? Freon will need to be added by someone.

Summary © Adding freon or topping off a cars A/C system is the most common task performed to restore performance and get cold air blowing again. However, adding refrigerant isn’t always the solution for car air conditioning problems – troubleshooting may be required before just charging a car AC system.

There can be many other things wrong besides a system being low on refrigerant. To diagnose/troubleshoot problems, an A/C manifold gauge set is needed to read high and low side pressure readings. Avoid adding refrigerant with a simple charging kit like the ones sold at parts stores. Don’t add any stop leak, this can cause problems in the compressor, expansion valve or condenser.

The image above was taken at Moog and US Hwy 19 in Tarpon Springs Florida, it made me laugh. The sign says “Your wife is hot! She wants her A/C fixed, let us check it for free”. For some help taking care of your AC problems yourself continue reading.

This is where it starts to get serious. Keep in mind that using an A/C gauge set and seeing BOTH high and low side readings can help in diagnosing the problem when you know what to look for. First, on a 134A system the high and low side service ports are different sizes. AC gauge sets have color coded hoses, the blue color coded hose has a connection that fits on the low side service port and the red hose has a connection that will only fit onto the high side. The yellow hose won’t hook up to anything if just checking the readings; it can be used to connect to a vacuum pump or attached to a refrigerant can or tank.

*Make sure the condenser fan comes on when the readings are being checked. Below are normal car AC pressure readings with 134A.

* Normal readings on high and low side with AC OFF (static pressure) – Depends on outside temperature, but normally is between 80-105 PSI * Normal low side reading with AC on high-speed and MAX & engine at 800-1000 RPM’s – Ranges from 25-35 PSI – Note that on many Chrysler products a normal reading on the low side may be 15-25 PSI

* Normal high side reading ranges from 200-350 PSI Don’t assume that if adding little Freon is good that adding allot is better! Overcharging just a little can decrease the performance of the system and possibly damage the compressor. Additional Car A/C Info – Troubleshooting Gauge Readings

With the AC on the coldest setting, use a thermometer in a middle vent. Normal vent temperature readings will vary depending on the (ambient) outside temp. The vent temperature should range from around 42-55 degrees in my experience. If normal gauge readings are obtained and the vent air is cold – STOP don’t overcharge the system. The only proper way to remove refrigerant is with a AC recovery machine so if this is being done at home I can’t emphasize enough NOT to over-charge the system. And actually the best way to insure the proper charge is in a system, is to use an AC machine to recover the freon and then evacuate and recharge the system with the correct amount. Most cars have the factory specified amount on a decal under the hood. See the next page for gauge readings and images. Continued on Page 2

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386 Responses
  1. Ronnie Kephart :

    Date: May 21, 2009 @ 10:48 pm

    Is my high side gauge bad if I can get the correct low side readings and the vent temperature is great, but the high side is only 50 psi?(Also, it reads the same on multiple vehicles) Will the gauges read the system pressure on both sides with the gauge valves closed. In other words, under what circumstances should the high side valve be opened(how about during vacuuming system down)?

    Thanks for the help and the website!!

  2. dennisb - Auto Tool Sales :

    Date: May 22, 2009 @ 6:30 am

    Ronnie, Sounds like the high side gauge is bad. The AC manifold gauge should NOT be open to read the car’s readings.

    Without an AC machine, charging is always done through the LOW side, so the only time the HIGH side ac gauge valve should be opened is during vacuuming the system down.
    Click the image below to see our AC gauge sets for sale on our main website.
    Ac Gauge set for sale

  3. greg :

    Date: June 27, 2009 @ 5:25 pm

    Using a/c gauges I’m getting 25 psi and low 150 on the high side and the fan keeps going off, any common causes?

  4. dennisb - Auto Tool Sales :

    Date: June 27, 2009 @ 6:52 pm

    Greg, assuming the blower speed is on high, AC is set on maximum and engine is around 2,000 RPM’s, those readings seem low. Seems like the system is undercharged. The condenser fan is most likely going off because of the high pressure not being high enough to require the fan.

  5. Todd :

    Date: June 29, 2009 @ 9:13 pm

    My silverado is blowing hot air. i am getting a reading off the low of 100psi…any ideas?

  6. dennisb - Auto Tool Sales :

    Date: June 30, 2009 @ 6:58 am

    Todd, as stated in the article BOTH readings should be checked to have a better idea of what is going on with an AC system but based on the limited information… the compressor is not engaged or is not pumping. Below are some things I would check;
    1. Check the high and low gauge readings with the AC on & set on MAX/Recirculate, middle vents with the engine at 2,000 RPM’s, blower speed on high.
    2. Check the vent temperatures with a thermometer from the middle vents, far right & far left vents?
    3. What is the outside temperature at the time the readings were taken? 4. Check to see if the condenser fan blowing strong?
    5. Notice if compressor clutch is cylcling excessively.

  7. Nathan :

    Date: July 5, 2009 @ 5:29 pm

    My a/c is blowing out semi cold air. When I check the low-side pressure with the a/c on max, high blower setting, and idle speed, the reading is 55psi (95deg F ambient). But when I hold the engine at 2000 rpms, the reading drops to about 40-45psi and then the clutch disengages. When i let the engine come back to idle, the clutch kicks back on. It does this constantly. Am I low on freon because of the reading at 2000rpm?

  8. dennisb - Auto Tool Sales :

    Date: July 9, 2009 @ 10:29 am

    Could be overcharged, not enough air going across condenser fins, compressor not pumping sufficiently… BOTH gauge readings are really needed to get a better idea.

  9. adam :

    Date: July 10, 2009 @ 12:58 am

    I have 1993 acura integra. I installed new compressor, orfice tube and drier. Its still not cold.The reading for the low side 40 psi to 55, the high side is 200 to 350 psi. The condenser fan works perfectly at a very high speed. When I drive at highway speeds, the temp inside the vent reaches 40f when I stop it reaches to 60 to 70f, whould you please help me out?

  10. dennisb - Auto Tool Sales :

    Date: July 10, 2009 @ 6:19 am

    Adam, I would have thought your car would have had an expansion valve NOT an orifice tube.

    But from what you are telling me, the AC works great at highway speeds and not at stops. My first thought would be the condenser fan, if there are two fans I would see if they both working. Also if the car’s engine temperature is running higher than normal at idle, there could be some heat transfer from the radiator to the condenser causing the AC not to work as efficiently.

  11. A/C Re-Charge - Chevy and GMC Duramax Diesel Forum :

    Date: July 15, 2009 @ 4:42 pm

    […] low side may be 15-25 PSI •Normal high side reading ranges from 200-350 PSI Here is a link Adding Freon to Car AC – Gauge Readings Explained | __________________ 05 Duramax LLY Bullydog Tripledog(Crazy Larry) w/ outlook monitor Last […]

  12. Mike :

    Date: July 24, 2009 @ 8:24 pm

    AC blowing warm. Took to service tech and he claimed air in the lines. They connected to ac recovery machine, reclaimed old 134a, pulled vaccuum, and charged. The process added .7 lbs to the sys which requires 1.7. So, I take it that my sys still had 1 lb before recycling. Air blows very cold now. Obviously I am concerned about how long this will last (after $149 to add 134a) Car is 1996 and ac issues began 2 yrs ago. Is it safe to say there is a very slow leak if there is still 1 lb of 134a after 2 yrs of warm air? If warm air reocurrs, can I just add 134a or will it need to be in a vacuum before adding?

  13. dennisb - Auto Tool Sales :

    Date: July 25, 2009 @ 7:12 am

    Mike, sounds like there has to be a small leak. On any older car like that, it wouldn’t be unusual to have small leaks. Some of the common causes are the front compressor shaft seal, compressor housing leak, service ports, hoses & evaporator. If UV dye is in the system, it may help later to determine the source of the freon loss. Also using an electronic refrigerant leak detector should be used if the problem isn’t obvious. I wouldn’t be too concerned at this point unless it got worse. The service technician was not aggressive and has got your air blowing cold for the lowest amount compared to most other repairs he could have suggested. By doing the evacuate and recharge (& most likely adding dye in case you come back) he’s given your car’s AC a new lease on life. Hopefully this will last at least a year before it needs some sort of service, but don’t be upset with the technician if something fails. To answer your question about adding freon. Most likely you can add if needed, this would be the least expensive option… if that doesn’t work then further diagnosis will be needed at that time.

  14. dane :

    Date: July 25, 2009 @ 2:34 pm

    03 toyota avalon, gauges read normal readings for temp, but the compressor is constantly cycling, and the normal readings turn into up and down movements, and high side reads really high (after cycle) then repeats… any ideas? ac is cold then hot then cold then hot….

  15. dennisb - Auto Tool Sales :

    Date: July 25, 2009 @ 3:32 pm

    Dane, since you say “the high side reads really high (after cycle)” I would suspect that the high pressure cut-off switch is shutting the compressor down to protect it from being damaged. Usually the cut-off switch will disable the AC compressor at around 500 psi to keep the compressor from being harmed. The most likely causes, could be;

    1. Too much freon in the system.
    2. Condenser not working, or not spinning fast enough.
    3. A restriction in the system, possibly a clogged condenser.
    4. Heat transfer from the radiator if the car is running hotter than normal.

    You may want to try spraying water on the condenser with a garden hose to see if the extra cooling, will allow the system to operate more normally.

  16. john doe :

    Date: July 29, 2009 @ 5:28 pm

    Hi, I have an acura integra 1993. My a/c doesn’t cool very well any more. The gauge set I have only allows for testing of the low side. My low side w/ engine off is at ~74psi, w/ engine on is at 35psi. The evaporator outlet line feels cool but the condenser outlet to the evap. is warm. Advice would be great! =(

  17. dennisb - Auto Tool Sales :

    Date: July 29, 2009 @ 8:00 pm

    Could be a number of things, if both gauge readings are not read it’s really hard to say. The static gauge reading indicates that the system may be a little low (indicating under-charged). The static reading can vary depending on the outside temperature.

    The low side reading (35PSI) if measured on MAX air, high speed blower and fans working could indicate that the compressor isn’t pumping sufficiently. It’s probably best however to have a pro check it locally that will have the benefit of having both gauge readings and physically being there to diagnose it properly.

  18. Alex :

    Date: July 30, 2009 @ 1:48 pm

    vw golf 2000. New drier, exp valve, condenser and rebuilt comp. Evaporator and hoses are old but flushed. Idle, low side 42, hi side 250. 3000rpm, low side 30 and less, hi 300-330 up and down constantly. If running the car for 30min will freeze and blower inside the cabin will blow low even if max blow selected. Turned the car off for few min, started again and blower was working again. Get another compressor? Appreciate the advice!

  19. dennisb - Auto Tool Sales :

    Date: July 30, 2009 @ 2:35 pm

    Alex, the compressor seems to be working sufficiently. The problem could be that the system has moisture in it (try a long vacuum) or that the expansion valve is not working properly. Either of these two things could cause the evaporator to freeze up. If the evaporator is iced up, the airflow will be reduced.

  20. Alex :

    Date: July 30, 2009 @ 5:21 pm

    Thanks for quick answer! Forgot to say that I did vacuum the syst. 40 min with robinair 2 stage pump. Problem is that on high rpm the low goes as low as 15psi, while the high is at 250-300.
    Any additional thoughts?
    Many thanks!
    VW golf 2000

  21. dennisb - Auto Tool Sales :

    Date: July 30, 2009 @ 7:33 pm


    The low side does seem a little too low. The expansion valve may not be working properly.

  22. Oleg :

    Date: August 6, 2009 @ 5:40 pm

    Hi. I got 02 Ford Explorer. Recently I noticed that my A/C is not working good at idle. So I hooked up my gauges and the low side is up in 60s, high about 230 at idle, but with a little rpms (about 2000) low side goes down to 35 and A/C works a lot better. Does that means that I need to look for a new compressor?

  23. dennisb - Auto Tool Sales :

    Date: August 6, 2009 @ 7:32 pm

    Oleg, Sounds like the AC compressor could be starting to pump a little less than it should. If the compressor isn’t noisy, I would try an evacuate & recharge to insure there’s no air in the system and the correct amount of refrigerant.

    Since you have an Explorer… If you haven’t already seen our blog on a common problem with Ford Explorer’s AC, check it out in case the recirculate door might be part of the problem.

  24. Trace :

    Date: August 7, 2009 @ 11:25 pm

    I have an after market system from Hot Rod Air in my car. The ambient was 90 deg. High side was 250 and the low was 20… The vent temp was 38-40 deg F. The gauge is working properly as I checked it on my daily driver and both high and low were in the norms. I’m not complaining about the cold air but something must be a little off. Any ideas?

  25. dennisb - Auto Tool Sales :

    Date: August 8, 2009 @ 7:17 am

    Trace, I see what you mean, the low side is lower than you would expect. But as long as the system isn’t getting so cold as to freeze up, I would enjoy the ice cold air! It’s possible though, that with a little cooler outside temperature, the evaporator could get iced up. If the system uses a temperature probe, I would try to make sure it is correctly located to accurately read the temp of the evaporator. If it doesn’t have a temperature probe in this aftermarket system, the expansion valve could be contaminated or malfunctioning. You might also check with the manufacturer to see if they have any suggestions.

  26. Chuck :

    Date: August 12, 2009 @ 5:56 pm

    I have a 2001 Ford Expedition with rear AC. The high side reads 180 psi and the low side 60 psi at 1500 rpms. Static test shows even pressure on both sides. Could I be over charged?

  27. dennisb - Auto Tool Sales :

    Date: August 12, 2009 @ 7:30 pm

    Chuck, If it were over charged, both readings would be too high. The high side should be higher than 180 psi and the low side should be lower than 60 psi. In your case the compressor may not be pumping sufficiently.

  28. dennisb - Auto Tool Sales :

    Date: August 12, 2009 @ 7:31 pm

    More About Dual A/C Systems

    With dual AC systems the readings may not tell the entire story sometimes. For instance, if the rear expansion valve isn’t working properly, the readings may look normal because there is no way to isolate the readings specifically for the front OR the rear. Usually if the front is cooling well, but the rear is not, the rear expansion valve will be the cause.

  29. wayne :

    Date: August 15, 2009 @ 3:15 pm

    thanks for the info.. we have issues all the time and im trying to get better educated in ac arena. this explanation is really helpful. thank you. we have a huge fleet of Hummer limos and if anyone is looking to work on our vehicles you can check us out at

    thanks again for the info i will pass it along to our other office

  30. Jose :

    Date: August 18, 2009 @ 11:07 pm

    I have a jeep an i just used one can of freon and it shows 500 psi the ac works good but the pressure is to high the low is 50Psi

  31. Jose :

    Date: August 18, 2009 @ 11:10 pm

    Why is the pressure of my Jeep so high and how do I lower it? I just used one can and it shows 500 psi.

  32. dennisb - Auto Tool Sales :

    Date: August 19, 2009 @ 6:23 am

    Jose, The system in your Jeep’s AC is most likely overcharged, assuming the cooling fan/fans are working and the engine isn’t overheating.

    In the old days to remove freon (before it was illegal) we would vent the refrigerant. We would slightly open the valves and have the yellow hose in a cup so we could measure how much refrigerant oil came out during the process. It is now illegal to remove freon this way due to damage that fluorocarbons can do to the ozone. The only legal method for removing refrigerant now is to recover it with an AC machine. I recommend taking your vehicle to a shop and have this taken care of. They will 1. Recover the refrigerant properly. 2. Vacuum the system down. 3. Add oil if needed. 4. Put the correct amount of 134A in the system. 5. Evaluate the AC system and other systems (like cooling system and HVAC air delivery) to make sure it is working as it should.

  33. dennisb - Auto Tool Sales :

    Date: August 19, 2009 @ 7:50 pm

    Please visit our car questions page listed at the top of the page for help with repair questions you may have. Thanks, Dennisb

  34. Chris :

    Date: October 4, 2010 @ 1:34 am

    HELP! PLEASE!? I have a 92 Ford Escort. The a/c was low on r-12 freon, so I bought the retrofit kit. It says under the hood that a proper charge is 2 lbs exactly. I pulled a vaccuum on it for over an hour. When I did though, I had to keep turning the vaccuum pump on and of and on and off until it stayed 15-20 below 0. Basically it wouldn’t hold the vaccuum until I got it below 10 and it would rise right back up and then I would turn it on. Anyway, I finally got it to stay vaccuumed and left it there for an hour. I used the included cans which were 14 ounces total each, which led me up to almost the proper charge. Anyway, it did get colder, but the coldest it gets is 62-65 degrees. I can live with that, but as soon as I get in and drive it at all, it stops being cold at all. Its only slightly cold at idle! The pressures are both 85-90 with engine off. With engine on: low is 30-55, and high has gone from 150 to below 100 now. The high side doesn’t move much at all, but the low side moves a lot! what do u think????? PLEASE HELP! btw, this is my first a/c work attempt.

  35. dennisb :

    Date: October 4, 2010 @ 10:11 am

    Chris, the fact that vacuum could not be brought down to 28-30 is a sign of a leak. First thing first diagnose the and repair the leak. Use a freon leak detector like the one below. Click on the image to see the product listing.
    Refrigerant leak detector

  36. Ben Orens :

    Date: October 5, 2010 @ 10:05 pm

    Looking for high pressure A/C line (adaptor.)
    93 Buick Road Master (R12) system.
    Male fitting at rear of compressor has check ball inside that is down inside about 3/8″.
    Need to connect charging line,high pressure and gages.
    Adaptor needs to trip the check ball so high pressure can be read on gages.

    Thanks, Please let me know

  37. dennisb - Auto Tool Sales :

    Date: October 6, 2010 @ 8:44 am

    Ben, make sure you aren’t looking at the high pressure releif valve which is usually on the rear of the AC compressor. Usually you will find the high side service port on the AC discharge line (hose going from comp. to condenser) or in the liquid line near the evaporator. The service manual says the high side adapter required is (3/8-24 threads). I would probably go to the local parts store and get retrofit adapters. Flush system, replace drier and evacuate and recharge with 134A and compatible oil.

  38. Miguel :

    Date: October 11, 2010 @ 6:48 pm

    Dennis, I have read most of your comments and I know to get accurate readings I have to hook up low and high side but until I do that I will tell you what is happening on the low side. With ac full blast I get no cooling off the ac. Low side reading fluctuates between 25-100 psi. Initially it starts at 25 PSI, the clutch on compressor kicks in pressure goes up to 100 psi then compressor clutch kicks off presuure then drops to initial 25 psi reading. This cycle happens every 10 seconds.

  39. dennisb - Auto Tool Sales :

    Date: October 11, 2010 @ 7:43 pm

    Miguel, sounds like low freon level, I also think you have reversed what’s happening. The pressure on the low side will read the highest with the compressor clutch dis-engaged and the lowest when the compressor is engaged.

  40. Rolando :

    Date: November 21, 2010 @ 11:32 pm

    I am glad I discovered this post.

    Well, I think in answering Miguel’s question, you might have answered mine, since I am having a similar problem. Right now I have only checked the low side port, and it is cycling up from 22 PSI to 43 PSI within a 7 second time period, and then back down from 43 PSI to 22 PSI within a 19 second period, for a grand total of approximately 26 seconds? What’s going on? This was done today, in Florida’s weather, evening time, I guess about 80 degrees, with the A/C on, in the setting right before max, which is number 3 on my 2003 Ford Explorer.

    I find myself adding freon about every six months, but it is needed a lot sooner than this because after I add freon, I believe it’s about a month after I hear the compressor cycling pretty often like it was before I added freon.

    I bought one of those products that’s supposed to inject a red dye into the system, but I don’t believe I saw any coming out. What I do see coming out after a few minutes of adding freon is a lot of dripping of water. I am not sure if that’s due to maybe the can being empty, but me not being sure, so I continue squeezing the trigger that’s pumping the freon into the system. I use one of those kits that bring the hose with the trigger and the ability to read the pressure.

    When I do add freon, the cycling happens at much longer intervals. Don’t remember the exact details, because I have been struggling with this problem for about 2 years now but haven’t had anything done other than buying cans of freon due to shortage of cash.

    So, what’s going on?

  41. dennisb - Auto Tool Sales :

    Date: November 22, 2010 @ 7:17 am

    Water dripping is normal condensation draining off the evaporator. Refrigerant leaks can sometimes be hard to find. See our car repair article about finding refrigerant leaks for more help.

    Checking for A/C Refrigerant Leaks – Car Repair Tips

    You may also want to invest in a refrigerant leak detector.

  42. barney stauffer :

    Date: January 8, 2011 @ 3:45 am

    without bothering you, i think you answered my question. i should put my hand in my pocket & pay a profesional. thanks

  43. plugged orface and blown compressor :

    Date: February 14, 2011 @ 9:58 pm

    I have a 1990 F250 that was converted from R12 to 134 and the cap tube became plugged and a blow out plug on the compressor released the 134. I need some kind of tool to get to the cap tube and open it up. Also is there any way to repair the blown plug on the compressor without replace?

  44. dennisb - Auto Tool Sales :

    Date: February 15, 2011 @ 6:24 am

    There may be an orifice tube repair kit available, which would require cutting the old one out. Flushing the AC system will definitely be a good idea. As far as the high pressure relief valve on the back of the compressor; usually once the pressure goes down the valve closes – if it DOES NOT close it will have to be replaced. Usually the cause of the relief valve to release pressure is from TOO MUCH pressure from 1. Not enough airflow across condensor. 2. The vehicle overheating causing head pressure to climb too high. 3. A restriction in the system, like a blocked orifice tube or clogged condensor from dessicant material escaping the drier. 4. OVER-CHARGING – putting too much Freon in will cause this everytime. Good Luck

  45. Richard :

    Date: February 24, 2011 @ 12:02 pm


    I am putting in a Vintage Air system in my 56 chevy, I am wanting to use Russell Proflex braided lines, my question is, does this braided hose carry enough PSI rating, I believe it is 1000 PSI. Please let me know and thanks Dennis.


  46. dennisb - Auto Tool Sales :

    Date: February 24, 2011 @ 12:31 pm

    Richard, The most I’ve seen car’s AC systems get up to is 500 PSI. Usually there’s a cut-off switch that will shut the compressor down around 450-500 psi to save the compressor from damage. So if your hoses are good for 1,000 PSI you should have no problems with them.

  47. justin :

    Date: March 2, 2011 @ 1:20 am

    thanks for all the great info. here is what i got. 2001 for expedition 5.4 rear aux a/c. replaced the compressor as well as the accumulator (sorry cant spell tonight lol)recharged the system. i was told 36 oz of freon and 11 oz of oil is needed for the system. all was going well, and then the clutch on the compressor started to dissegauge every 10 seconds then engauge for 7 sec. back is blowing ice cold but the front isnt, do you think i have a blockage in the orifice tube, low side is all i gould gauge but it is static at 60 psi when the clutch is engauged it drops to 24 or so and when it is off it goes up to 36 or so, any ideas

  48. dennisb - Auto Tool Sales :

    Date: March 3, 2011 @ 7:29 am

    Justin, sounds like a restricted orifice or expansion valve in the front. I would be careful not to add too much oil. 11 ounces seems like a lot unless you have thoroughly flushed and removed ALL the oil that was in the system previously. It’s important to know that many compressors come with oil already in them too. It’s best to drain and measure (and refill) them to know how much is going in – unless the compressor paperwork tells you. You have to manually turn the compressor clutch plate while draining to get all the oil out.

    If a system has too much oil, the system’s cooling can be affected and sometimes the cycling switch can be full of oil and not cycle the compressor properly. Since the rear is cooling, the compressor is probably running enough, so I would look into the front expansion/orifice. Good Luck

  49. mike :

    Date: March 30, 2011 @ 11:43 am

    Great info on this site, thanks. My mom has a 97 chevy malibu who’s a/c stopped working. I hooked up my a/c manifold gages to see if I could fix it for her and got really low static readings, 35 low side, about 45 high side. With the car turned on I got the same readings. When I turn the ac on I do not hear a click or anything, so I do not believe the compressor is engaging. Might the compressor not be engaging because the pressures are so low? I don’t want to add any more freon since the low side pressure is already at 35. Is there anything more I can check before I tell my mom to take it to a shop? Thanks for any help!

  50. dennisb :

    Date: March 31, 2011 @ 8:48 am

    Mike, low static pressure (AC clutch NOT engaged) indicates refrigerant charge is too low. When the system is undercharged to a certain point, the compressor will not be allowed to be turned on for it’s own protection.

    A common leak on the Chevrolet Malibu (and most Chevy’s) is the AC compressor, where the housing comes together. Look for residue from a leak on the underside of the compressor. Good Luck

  51. Terry :

    Date: April 4, 2011 @ 8:17 pm

    My dad replaced the a/c high pressure switch cut out on my 95 Olds 88(K)and the 134 blew out (he was told it wouldn’t). Do we need to add oil to the compressor?

  52. dennisb - Auto Tool Sales :

    Date: April 4, 2011 @ 9:03 pm

    Terry, it all depends on how much oil was lost. I would think that adding an ounce or two should be ok. The only way to know for sure is to remove the compressor, drain and measure the amount. Also the drier should be changed. Also it’s important to know that the high pressure relief valve seldom just leak – they normally will release refrigerant if the system is over-charged or if the fans are NOT working. Good Luck

  53. Terry :

    Date: April 5, 2011 @ 2:40 pm

    Thank you for your real quick answer. Actually the high pressure relief didn’t leak. My compressor would not always turn on, and so my dad was told that the high pressure switch should be replaced,and when he replaced the switch the 134 blew out. The low pressure valve does leak though (I have a new one to put on). Now hopefully I can get my dad to remove the compressor, he was hoping that he could just add some oil while adding the 134.

  54. dennisb - Auto Tool Sales :

    Date: April 5, 2011 @ 2:48 pm

    OK, so it was actually the high pressure switch and NOT the high pressure relief valve. I would most likely estimate how much was oil lost and just add UV Dye / oil to the system. And then evacuate and recharge the system. Good Luck.

  55. Terry :

    Date: April 5, 2011 @ 4:12 pm

    @dennisb, yeah just the switch. Thanks for your help!

  56. Terry :

    Date: April 5, 2011 @ 5:04 pm

    @dennisb, my dad doesn’t really want to replace the dryer, since the system was only open for about 5 minutes. Do you think it is necessary to replace it since it wasn’t open for much time? I could possibly talk him into it, if I gave him the reason :)

  57. dennisb - Auto Tool Sales :

    Date: April 5, 2011 @ 5:27 pm

    The dessicant life-span is around 5 years in a sealed system. Anytime the system is opened it is recommended to be replaced. When comes down to it, it’s your decision. Good Luck

  58. Terry :

    Date: April 5, 2011 @ 5:31 pm

    @dennisb, good reason to change it then! THanks

  59. Fritz :

    Date: April 6, 2011 @ 12:14 am

    just replaced compressor on a 95 gt Mustang, flushed system replaced drier.
    Pulled vacuum to 30hg and checked for leaks. All was good. Started adding Freon 1.4 lbs aprx. Compressor cycled, sucking in Freon. The Vent temp dropped from 80 to 65 and than suddenly low pressure went from 35 to 90. High side the same. Compressor quit cycling. Replaced pressure switch on high and low side from another Mustang that we know are good. Wwhat gives? Thanks for any ideas what it could be. Compressor possibly broken? A/C switch not working? Checked clutch fuse as well and is good!

  60. Terry :

    Date: April 6, 2011 @ 12:17 am

    @dennisb, I like your site it is designed very nicely. Thank you again for your help, I got the dryer and my father is going to put it on for me.

  61. dennisb - Auto Tool Sales :

    Date: April 6, 2011 @ 6:37 am

    Fritz, I would check to make sure there’s power and ground to the clutch coil. It needs power and ground to engage the clutch. The coil acts as an electro-magnet and magnetizes the clutch when energized. If it’s getting power and ground, then the clutch coil could be faulty or there’s too large of an air gap between the clutch disc and hub. If there’s no power, you may have to get a wiring diagram and bactrack through the circuit to pinpoint the problem. Common causes of loss of power to the clutch coil could be a poor connection, bad low pressure cycling switch and sometimes a high pressure switch. You are also on the right track to check fuses too. I like to check ALL fuses just to eliminate something simple. Many cars have fuse boxes in two or three locations! The Mustang, I believe has one fuse panel in the passenger compartment and one under the hood. There could be more than one fuse related. Sometimes it’s easier for me to check ALL the fuses, because by the time I look them up in the repair manual, I could have checked them all with my power probe. Good Luck.

  62. Fritz :

    Date: April 6, 2011 @ 9:12 am

    Thanks I will check that out!
    I also was thinking the a/c switch was faulty but kind of strange it would fail during charging.

  63. Fritz :

    Date: April 11, 2011 @ 12:30 am

    Okay so I got a few days to check out
    the Mustang Gt AC. It holds Freon so no leaks! I noticed when car is cold and I turn on AC switch, compressor cycles, however as soon as car warms up, it stops cycling. So I jumped compressor and it cycles on, low and behold Air is cold so I added freon and I got it down to 38 degrees. So I know now that compressor works. It is not a fuse.
    The AC relay is good because I switched it out. Now I’m thinking the control inside the dash is defective. What do you think?

  64. alfactors :

    Date: April 16, 2011 @ 11:57 am

    1994 dodge shadow comp. ingaged whin ac on but low side is 0 hight side 110 y is it running with 0 on low side try to put 134 in wont vac it in.?

  65. wrong :

    Date: April 17, 2011 @ 8:08 pm

    I have attempted to put freon in a 1994 gmc sonoma. Only a small amount of freon will go into the unit. The ac is blowing hot air and when a small amount of freon finally went into the unit, the air conditioner got a little cool, then went back to warm air. Does this mean there is a leak? If so, what is the most common place to check for leaks?

  66. adam :

    Date: April 18, 2011 @ 11:37 pm

    I have 1999 Astro with dual a/c I replace new ac compressor and orifice tube and charged the system. I have reading for low side 40 psi and the high side 150-180. The rear ac very cold, the front not cold, the dryer is not cold its warm, the line go from dryer to compressor is warm, the evap is warm. The compressor engages at 150 psi high and the low side stay at 40psi not lower. When disengage low side 50-60psi and high, any idea? Thanks

  67. dennisb - Auto Tool Sales :

    Date: April 19, 2011 @ 6:37 am

    Adam, I would have vacuumed the system down at least 30 minutes before charging the dual AC system. Air trapped in the system can make it much less efficient. If you did have the vacuum pump on the system for a good evacuation before charging, seems like the compressor may NOT be pumping quite enough. I would check the readings with the RPM’s around 1500-2,000. If you still have 40 Low and 180 High, the compressor is not pumping sufficiently. If you need more help and suggestions, visit our car question page to ask a Chevy Tech. Good Luck.

  68. Fritz :

    Date: April 23, 2011 @ 11:58 am

    Okay so I was having intermittent clutch cycling problems. I replaced hose with built in orifice,(Ford).Thinking it was clogged.
    I believe the problem is fixed and it all leads to the wiring on the High side pressure cycling connector.
    Two wires are slightly exposed of the four. As I jiggled it,the compressor cycled on. I will now order new connector.
    These Cars are getting older and the connectors,wiring, all are degrading to the high heat temp under the hood in these vehicles. A/C works very well and cools with 24 oz freon,versus 32oz that Ford shows on the sticker.The vent temp at 85 outside air with 50% hummidity is in the mid 30’s on high setting and at normalsetting in the low 40’s.

  69. dennisb - Auto Tool Sales :

    Date: April 23, 2011 @ 6:53 pm

    Glad to hear your AC will be no longer on the Fritz!

  70. PT :

    Date: April 23, 2011 @ 8:33 pm

    I have a Vintage Air system on a 454. My safety switch failed after I installed electric fans. Replaced it and then evacuated the system for one hour. I let it sit for an hour and it maintained 30″ of mercury–no leaks. Next, I added 12 oz’s and then another 12oz of 134a. I still have 4.5ozs to go but it is going way sloooow and my pressures seem out of whack. I’ve quit adding 134a. My low side seems very high and my high side seems real low. Cabin temp at the vent is 60F with an OAT of 76F. I have a 90PSIg reading on the low side and a 100PSIg reading on the high side. Suggestions? Thanks

  71. dennisb - Auto Tool Sales :

    Date: April 24, 2011 @ 8:59 am

    PT, higher than normal low side readings and lower than normal high side readings indicate that the compressor is NOT pumping sufficiently. If both readings were LOW, it would indicate low on refrigerant. Good Luck.

  72. Ron :

    Date: April 25, 2011 @ 6:08 pm

    What happens if you add refrigerant to your auto ac (on the low side) without the compressor on?

  73. dennisb - Auto Tool Sales :

    Date: April 25, 2011 @ 6:12 pm

    Ron, not much will go in. The compressor usually helps to draw in the refrigerant, Shops that use AC machines have the choice of having the car draw in the refrigerant or they can use the machine to put the refrigerant in without the car and AC compressor running.

  74. Jim :

    Date: April 28, 2011 @ 8:29 am

    First, thanks for the great article.

    The article states that on some Chrysler products a normal reading on the low side may be 15-25 PSI.

    Any idea if this is true on my ’03 Neon. I must replace the high pressure hose (small leak) and I am anxious to use my new gauge set and to hopefully learn just a bit.

    Thanks in advance!


  75. dennisb - Auto Tool Sales :

    Date: April 28, 2011 @ 10:45 am

    Jim, It most likely will be between 15-25psi. Keep this in mind when charging. Also more is NOT better and finally, cold air coming out of the vents is the true test!

  76. Jim :

    Date: April 28, 2011 @ 10:48 am


    Thank you for taking the time to answer questions here!


  77. richard :

    Date: May 4, 2011 @ 11:23 am

    Dennis I have 1997 gmc savanna low side is 25psi with a/c on max and compress. engaged. high side is 80psi

  78. dennisb - Auto Tool Sales :

    Date: May 4, 2011 @ 12:22 pm

    Richard, based on gauge readings the system is low.

  79. joel :

    Date: May 8, 2011 @ 11:11 pm

    what will be the proper gauge of low and high freon on my honda civic 1.5 engine 99 model

  80. dennisb - Auto Tool Sales :

    Date: May 9, 2011 @ 6:41 am

    Joel, the readings in the article can be used as a general guide line for just about every car including yours. If you want more specifics you may want to ask a Honda Tech by using the Car question box on our car questions page.

  81. wally :

    Date: May 14, 2011 @ 5:45 pm

    I replaced a high pressure line on my saab 9-5. system was opened, but plugs inserted. recharged w/2 cans freon, low pressure read 40 and climbed to 45 when compressor kicked in. Worked fine for 5 days. Not cooling today, low side at 75, have checked w/yellow dye and nothing obvious. thanks

  82. john :

    Date: May 16, 2011 @ 9:26 pm

    Have a 2002 Dodge Caravan dual ac. I replaced compressor, expansion valve, and drier, let it sit for an hour on the 2 stage pump and then charged with 2.8 lbs of freon. My gauge reading were low side 40 and high was about 250 the problem is, is the vent reading was only about 60 deg, with it being about 80 deg out side. For a while it sat at low side 45 and high about 160 then it just switched to the readings above. Low 40 high 250

  83. Ralph :

    Date: May 27, 2011 @ 8:52 pm

    1995 Corvette-standard not electronic dash control. A/C blows nice and cold anytime-out.temp 75-100 degrees. However after about 10-15 minutes it freezes up and I have to turn if off for 5-10 min for the evaporator to thaw out. Any Thoughts?, Ralph

  84. dennisb - Auto Tool Sales :

    Date: May 28, 2011 @ 7:15 am

    Ralph, usually evaporator freeze up can be caused by several things. 1. Moisture within the system. A new dryer and using a vacuum pump to draw the the system down can remove the moisture from within. 2. Too low of pressure in the evaporator. This can be because of a partially restricted orifice tube or expansion valve. 3. Water not draining off the outside of the evaporator and out the drain tube quickly. This may be because of a restricted (or clogged) drain tube in the bottom of the drain hose.

  85. Joel White :

    Date: May 29, 2011 @ 10:33 pm

    Have a question, 2000 Grand AM merely blows cold air. I am getting a static reading of 32 on the low and 35 on the high. At operating pressure I am getting 26 low and 35 high. The systems was properly charged with a Robinair 34788 machine. Any ideas? Thank You and have a blessed day.

  86. paul :

    Date: May 30, 2011 @ 1:21 am

    I had a compressor seize up on a 2006 mazda3. I replaced it with a new one, and replaced the expansion valve and drier. I didn’t flush, because there was no debris in the compressor oil when I drained it. I added about half the freon the system takes, to about 60psi static (outside temp is 75). Started car, ac on, and low side pressure climbs to 35psi at which point belt starts squeeling. High side pressure was 100 psi. Any thoughts? seems like compressor is trying to stall, but if I had a blockage wouldn’t low side be really low and high side high.

  87. Mnk :

    Date: June 2, 2011 @ 1:08 pm

    Over the winter, my 1990 Ford A/C (converted to R134a) lost pressure, I guess, in part, because I did not run it to lube the seals. I added a can of sealer, then recharged the system using an all-in-one refrigerant/gauge kit. At about 35psi, the air was 70F at the center vent (ambient temp 85F). Adding another 12oz did not lower the temp.

    I have since purchased a good gauge set and have determined that the leaking has stopped, i.e., over one month, the psi has remained constant.

    But . . . static pressures are LOW-145, High-150; running pressures are LOW-60, HIGH-280.

    Before I purge/exhaust the system, am I correct in assuming that the most likely cause is air in the system? Any other possibilities?


  88. dennisb - Auto Tool Sales :

    Date: June 2, 2011 @ 1:25 pm

    Mnk, judging by the static pressures and pressures when the system is running, the system is overcharged – see the images in the article above. The sealer can cause a restriction in the condenser and orifice, so I would never recommend adding stop leak. It may not be causing a problem at this time for you, but I wanted to mention this for the benefit of other readers. In fact many shops will refuse to even hook up their expensive A/C machines if they know there’s “stop leak” in a system.
    After the system has the correct amount of refrigerant, I would then diagnose it – if problems are still present. Good Luck.

  89. Mnk a.k.a. Monk :

    Date: June 2, 2011 @ 5:41 pm

    You know you’re getting old (69) when you misspell you name.

    First off, thanks for the speedy response. I also know what you are saying about stop leak and gauge sets-A/C equipment. Over the years, maintaining my A/C in a what is now a fleet of rusting old cars, I’ve always blown out my gauge sets/hoses with compressed air. Don’t know if it helps; it’s a feel-good thing, at least.

    So . . . I bled off my refrigerant (into an empty 20lb propane tank which a local shop will purge for me). My current readings in 98-degree ambient air are:

    Static (engine cold): L/H – 90psi;
    Running (engine hot): L – 35psi; H – 230psi;
    Center console temp dropped to 60F.
    These readings were taken with the truck idling. My experience is that the console temp might drop another 5F on the road given better radiator/condenser cooling as well prolonged cooling of the dash and ducts.

    FYI, two years ago after I switched over from R-12, the console temp at idle was about 45F (40ish on the road).

    Thanks again,


  90. dennisb - Auto Tool Sales :

    Date: June 2, 2011 @ 6:43 pm


    69 is the new 39 right? Those readings seem a lot closer to what they should be. If you are not on MAX or (Recirculate) the system may get a little colder after changing that setting. Also the outside temp does play a large role in how cold the inside air will get. 98 outside is pretty warm especially for a car that is sitting at an idle. Condenser airflow is always something to check. Make sure the condenser is clean, has straight fins and the cooling fans are working properly. Good luck

  91. Monk :

    Date: June 2, 2011 @ 8:12 pm

    39? That was Jack Benny. What keeps me young is I still ride my ’96 Harley (FXDL) and trying to keep either the ’90 truck or a ’94 voyager running (when one breaks down the other serves to get parts).
    Speaking of old, I said ’90 Ford: it’s actually a ’90 Chevy 1500 pickup. Yep, OLD!

    I was surprised by the drop in temp after I bled off some refrigerant because when I first recharged the system after the sealer, I could not get the temp below 70???

    So, if it continues to put out 55-60F, that’s good enough for me. Just for future reference, am I correct in thinking that if there is air in the system, that air will cause the system to prematurely reach normal operating pressure but result in decreased cooling since air + refrigerant = less cooling than pure refrigerant?

    I really appreciate your gift of time and expertise. Thanks.


  92. dennisb - Auto Tool Sales :

    Date: June 2, 2011 @ 9:20 pm

    Sure, if there’s air in the system the efficiency will be decreased.

  93. Greg S. :

    Date: June 3, 2011 @ 11:24 am

    I have a 2000 Saturn that a bracket rubbed a pin hole in the condenser coil. Will JB weld fix this?

  94. dennisb - Auto Tool Sales :

    Date: June 3, 2011 @ 11:29 am

    Greg, JB is good stuff, but I don’t think it will work for that. High side pressure could reach 300psi. I would either replace the condenser or take it to a radiator shop to see if they can repair it.

  95. derek m :

    Date: June 3, 2011 @ 4:26 pm

    i have a 1998 chevy mailbu with 113000 miles ac blows cold kind of but not like it should and on the low pressure side it is running at 7psi

  96. dennisb - Auto Tool Sales :

    Date: June 5, 2011 @ 6:31 am

    Derek M, 7 psi is very low. You already know that from reading the article above. High side reading?

  97. clinton :

    Date: June 6, 2011 @ 9:56 pm

    2003 dodge 1500 4.7 engine …low side reads 14 psi and high side is 270 ,,if I add anymore freon the compressor starts to lock up.

  98. dennisb - Auto Tool Sales :

    Date: June 6, 2011 @ 10:38 pm

    Clinton, I would suspect a bad expansion valve. First I would have a shop remove the refrigerant, vacuum and recharge with the proper charge and recheck. The compressor seems to be pumping enough but the expansion valve may not be allowing enough freon through. Fig. 3 shows gauge readings when the expansion valve is stuck closed all the way (similar to your readings). Good Luck.

  99. Chris :

    Date: June 6, 2011 @ 11:28 pm

    Hello I see all your posting and I have a quick question? I have a 2001 Mustang GT just recharged the ac on the low side 25 – 30psi the car is running and blowing cool air…But on the high side 105psi that with the car off. is the ok..I don’t want to overcharge my ac unit. Any advice would be appreciated. Thanks

  100. dennisb - Auto Tool Sales :

    Date: June 7, 2011 @ 6:45 am

    Chris, the ambient temp. will effect the static reading (pressure with system turned off). The higher the outside or ambient temp. the higher the static reading. If you have the proper charge, the system will perform at it’s best. Anything more or less and the A/C system will not cool as well. High side readings? If the vent temp (while controls on MAX) is from 40-55 degrees it’s a pretty safe bet the system is NOT overcharged. Good Luck.

  101. Matt :

    Date: June 7, 2011 @ 9:45 pm

    I have a 2001 Honda Civic and the AC compressor clutch seems like it won’t engage on its own. If I smack it with a tool the clutch grabs and spins but if I rev the engine the clutch disengages again. I only have a low pres gauge and it reads 25 at idle but if I rev to 2000 rpm, the pressure drops to 10 and then kicks off the compressor. When the compressor is engaged, the vents blows cold air. Should I assume its low on 134a?

  102. dennisb - Auto Tool Sales :

    Date: June 8, 2011 @ 6:39 am

    Matt, sounds like a bad coil. I recommend taking it to a shop that can check it out more thoroughly. Good Luck.

  103. Tim :

    Date: June 8, 2011 @ 8:30 pm

    I just replaced the conpressor (reman), evap, condenser, expansion valve, drier on my 95 Maxima due to compressor failure. After pulling vacuum for an hour and recharging, I’m getting 55 on the low side and 150 on the high side with only cool air coming out while running at 1500 rpm and 80F. I’m thinking that the compressor is bad and can’t pull enough low pressure. What are your thoughts? Thanks.

  104. dennisb - Auto Tool Sales :

    Date: June 9, 2011 @ 6:23 am

    Tim, I think you are right. The compressor may not be pumping enough. Good Luck.

  105. Matt :

    Date: June 10, 2011 @ 11:14 am

    Hi Dennis, Before I rip out the compressor and replace the coil let me ask you this. Around the same time the AC clutch started acting up, the car had a tough time starting. When I checked the battery the cables were badly corroded mainly the Red + cable had acid all within the cable. I soaked it in baking soda to neutralize the acid and the cleaned it up as good as possible. The car starts fine now and I have the same battery which is still good. Could a bad battery cable cause the AC clutch to malfunction with a weak current? I don’t know the wiring diagram enough to know if the current is supplied from the alternator or battery but it seems coincidental that both would happen at the same time.
    Thanks again

  106. dennisb - Auto Tool Sales :

    Date: June 10, 2011 @ 11:26 am

    Matt, low pressure can make the coil cut off. When you rev the engine the low side pressure could go down low enough to make the compressor go off. If the coil is getting power but not engaging, it could be a weak coil or too large of an air gap. Which would make sense that when you wack it, it engages. A good repair shop will do some testing to see what the problem is before taking anything apart, which is why I suggested taking it to a repair shop. Good Luck

  107. Dustin :

    Date: June 13, 2011 @ 1:37 pm

    93 Ranger has R12 and gauge reading fo 25-50 on low side and 120-140 on high side. Is it low on Refrigerent or maybe a bigger problem

  108. dennisb - Auto Tool Sales :

    Date: June 13, 2011 @ 2:04 pm

    Dustin, Sounds like it may be low on refrigerant or the compressor not pumping enough, could be a bigger problem depending on the leak… Service ports may leak a little over time on any vehicle. If there’s a fast leak – say more than 1/2 a pound a year it should be fixed. Use dye or an electronic leak detector to pinpoint the source of the problem. It may be a good time to update to 134A. Good Luck.

  109. Todd :

    Date: June 13, 2011 @ 5:24 pm

    I have a 2004 Volvo S80. I am wondering if having too low and overcharged freon will cause the air to blow cold and hot air?
    It will blow cold for an hour or so, and then start blowing hot for 5-15 minutes. any ideas?

  110. dennisb - Auto Tool Sales :

    Date: June 13, 2011 @ 5:43 pm

    Todd, low freon is undercharged, not overcharged. Sounds like the amount of freon may be alright since it’s cooling ok until a certain point when something happens to affect it. The things I would look at when diagnosing the problem when it is acting up, is the possibility of a bad clutch coil or a frozen evaporator.

    1. A bad coil often causes the compressor NOT to come on when it should. The outer part of the clutch, called the clutch disc is engaged by the coil. The coil is like an electro magnet which allows the compressor to be turned on and off. The system will cycle the clutch on and off many times during normal operation depending on several factors, one being the low side pressure.

    2. If the system has moisture inside the system it can freeze preventing operation. Another cause of the evaporator freezing up can be the lack of cycling of the compressor. If the compressor stays on all the time or at least too long, the pressure in the evaporator will become too low and freeze. When the water on the outside of the evaporator reaches 32 degrees, it forms a sheet of ice blocking the flow of air. Restricted airflow means the heat and cold transfer cannot take place properly.

    Either of these things could cause an intermittent problem with cooling. Good Luck.

  111. Sean :

    Date: June 13, 2011 @ 6:35 pm

    Hello and thanks in advanced for any help you may bring.

    I own a 2002 Subaru legacy GT. I regretfully tried to save money and I bought a home refill kit with gauge. I followed all instructions and emptied the 18 oz can I to the low side. After I refilled I let the car and AC run and the compressor belt started screeching very badly and kept stopping and starting again draining power from the engine. The high and low hoses both get EXTREMLY hot to touch. The compressor seems to work fine until the car has warmed up completely. Did I overfill my system and ruin it?

  112. dennisb - Auto Tool Sales :

    Date: June 13, 2011 @ 6:43 pm

    Sean, the compressor could be seized or “locked up” or the system may just be over-charged. More isn’t always better. If I were checking the system, I would recover the system (use an AC machine to take the freon out) then pull a vacuum and recharge with the proper amount of refrigerant. After that recheck the operation, to see what we have. Good Luck.

  113. Tom K :

    Date: June 13, 2011 @ 10:49 pm

    Thanks for helping folks out. I need some help myself. 1996 Jaguar XJS. A/C got weak last summer and a friend evacuated and charged it and it started working great. What I am assuming is a relief valve let a bunch of refrigerant go a few days later. Put my recently purchased gauges on it a few days ago and it read maybe 5 psi on the and 200 on the high side on a 95F day. Tried charging and the low side came up to about 20, but the high side quickly started going up to 450. Got scared and took it to a chain offering $30.00 A/C diagnostic. They had me pay to evac and charge it, and then said bad compressor. That didn’t make sense to me, since the high side seems to indicate it can compress plenty. Added refrigerant and high side went way up again. Drove for a while before it let a bunch go again. I promise not to donate any more refrigerant to global warming. My best guess is expansion valve is clogged. Any ideas?

  114. dennisb - Auto Tool Sales :

    Date: June 13, 2011 @ 11:52 pm

    Tom, Sounds like an expansion valve to me also. It’s common for the low side to be very low and the high side to go up too high when an expansion valve sticks closed. Adding refrigerant just makes the high side go higher due to the restricted flow. I recommend having a shop recover the refrigerant with an AC machine, perhaps you could get the shop that you took it to previously to take it out for you since you just paid them for a check. Then you can change the expansion valve safely, without harming any Unicorns. Good Luck.

  115. Ben :

    Date: June 14, 2011 @ 4:10 pm

    1995 Ford F350, compressor replaced about 8 years ago, now just blowing warm air, and the compressor engages about every 10 secs or so.

    Static Test:

    Low – 14
    High – 14

    Running Test:

    Low – Approaches down to 10 psi, then when the compressor kicks in, it drops to -5, then when compressor kicks out, it once again travels back to around 10 psi before the compressor kicks in and drops it back to -5 psi again.

    High – 32 psi, then when compressor kicks in, it rises slightly to about 39 psi, until the compressor kicks out again, it drops back down to around 32 again.

    Based on your this article, I could assume an indication of low freon, and since the low side hits a -5 vacuum, maybe a bad exp valve?

    And to top off this, the yellow hose on my gauge manifold has no way to pierce a can of freon. There should be an adaptor or something if using one of those little cans of freon, wouldn’t ya think? haha

    Thanks for any help! Take care…


  116. dennisb - Auto Tool Sales :

    Date: June 14, 2011 @ 4:44 pm

    Ben, sounds like low on refrigerant. I would think that the expansion (orifice) tube is ok. The low side is doing what’s expected with the system so low. Adapters are available on our main website ( There’s a side can tap below, click on the image to see the product listing.
    Can Tap

  117. Tim :

    Date: June 14, 2011 @ 9:09 pm

    Hi Dennis,
    I just replaced the conpressor (reman)again (from AdvanceAuto Parts – a Gilmore Products #67453 unit) on my 95 Maxima due to 1st reman. compressor not operating correctly (see above). After pulling vacuum for an hour and recharging, I’m getting 65 on the low side and 120 on the high side with only warm air coming out while running at 1500 rpm and 65F. I’m thinking that this compressor is also bad and can’t pull enough low/high pressure. What are your thoughts? Thanks.

  118. dennisb - Auto Tool Sales :

    Date: June 15, 2011 @ 6:44 am

    Tim, sounds like this one is pumping less than the last one (could be a bad expansion valve, but most likely the compressor). Remanufactured parts can sometimes be very frustrating to deal with. The cost factor makes it a necessary evil though. I once installed 6 defective starters in a row on a Mustang… finally on the 7th one I got a good one. You start doubting yourself when you get a series of bad parts like that. Here’s hoping that 3’s a charm. Good Luck.

  119. Tim :

    Date: June 15, 2011 @ 12:14 pm

    Just checked it again and it reads 70/110 at 80 degrees. Pressure quickly equalizes when I shut off the A/C. Wll try another one and see what happens – hope I don’t have to argue too much with Advance Auto on this 2nd return. Thanks.

  120. Pat :

    Date: June 15, 2011 @ 4:55 pm

    I have a 2003 Envoy SLT, we live in the Phoenix area, yesterday it was 108, got in my car after coming out of a store, started my truck, the air came on for a few seconds, and started blowing hot air, looked at the outside temp and it read -29, I laughed, and adjusted my temp knobs to 60, still hot air, shut off car and back on, still reads -29. and hot air,, any clue what is wrong?
    Thanks a lot

  121. dennisb - Auto Tool Sales :

    Date: June 15, 2011 @ 5:11 pm

    Pat, I would normally suspect that the ambient (outside) temperature sensor may be bad because of the negative reading. But, since the AC is not working, all at the same time, it could be a controller (HVAC Control Head) or BUS communication problem. A scan tool and repair manual information will be needed to check this one out. Good Luck.

  122. herb :

    Date: June 15, 2011 @ 9:55 pm

    Great site! Best info i have found. My 2000 town and country cools great on the road but in town not so good. I find if i run the trans in gear 3(more rpm) it cools better. we have 100 temp–texas. Why does it take so long to cool and not cool at low rpm.

  123. dennisb - Auto Tool Sales :

    Date: June 15, 2011 @ 10:46 pm

    Herb, if the AC only cools well while the vehicle is moving – the AC condenser fan (or radiator cooling fans) may be inoperable. If the fan is working properly, based on what you have described, the compressor may not be pumping at a high enough rate. When you increase the RPM’s of the engine, the compressor is turning faster also. So if a compressor is weak, you may notice the air cooling sufficiently only when the compressor is made to pump at it’s fastest. A tech with AC gauges will be able to troubleshoot this further. Good Luck.

  124. Marty :

    Date: June 16, 2011 @ 2:56 am

    Thanks for the gage readings for 134A. Here in sunny AZ and with my ’03 Nissan Maxima, I was having to wait sometimes 3-4 minutes after starting for the A/C to start cooling and the condenser fans to start. Tonight with my new gage set and adapters and a can of R-134 I added a little at a time until I got a ‘steady’ 30 low and about 145-148 high at about 89 degrees ambient. Took me about 1 hour. Now even with the windows open, the discharge is very cold (forgot to do the digital temp gage) then turned it off to allow both sides to equalize. About 45 minutes. Started the car, turned the AC on and seconds later the compressor started and then almost immediately, the high speed condenser fans cycled on. Don’t have a leak detector but Nissan uses a UV dye so now I need to find the leak. Eveything looks very dry at 76000 miles. I just didn’t know the pressure/temp numbers like I used to with 12 and 22 systems. My new gages have a R-134 scale. I think I am darn close to an optimum charge. What do you think? Should I add more until I get close to 35 low and 160-180 high at about the same ambient?? Your advice is appreciated and an answer to my email would be terrific. Thanks

  125. dennisb - Auto Tool Sales :

    Date: June 16, 2011 @ 6:41 am

    Marty, thanks for purchasing the gauge set from, we appreciate your business. The only way to know 100% about the correct charge amount even for a professional is to put the factory specified amount of refrigerant in, after completely recovering and evacuating the system. With that being said, using the gauge readings and dash vent temp reading can help in making an educated guess (without doing the forementioned). The dash vent temperature with the system on MAX/RECIRCULATE, should be between 40-55 degrees (windows closed). The high side of 145-148 you mention seems low (RPM’s at 2-3,000). The high side should be around 200 or a little more. If adding more refrigerant I would monitor the low side to make sure it stays around the 30psi mark. Good Luck.

  126. Tim :

    Date: June 16, 2011 @ 5:14 pm

    Well, Advance Auto replaced the compressor again without a problem and the third one works good – 25 low/230 High at 1500RPM and 82 degrees outside. Hope it lasts at least three years to get my son through college! Thanks.

  127. dennisb - Auto Tool Sales :

    Date: June 16, 2011 @ 5:57 pm

    Tim, thanks for letting me know how this saga turned out.

  128. albert :

    Date: June 18, 2011 @ 10:16 am

    compressor clutch failed on 99 suburban with dual evaporators. replaced orifice tube, accumulator, and compressor. charged and front a/c working great. rear expansion valve was out so i evacuated, vacuumed, replaced accumulator, orifice tube and expansion valve. added oil and r-134. no leaks. low side 40psi and hi at 200psi with compressor running. ambient temp of 84. venting at 65 to 70 f on both front and rear. any suggestions? thanks.

  129. dennisb - Auto Tool Sales :

    Date: June 18, 2011 @ 10:29 am

    Failed clutches are not that common on GM’s. Usually it is a locked up compressor – the clutch will overheat, but is not the root cause typically. I mention this because if the compressor has locked up, the system could be contaminated and should be flushed before installing a new compressor and related parts.

    If the readings that you’ve given are with the AC on MAX (Recirculate) at 1500-2000 RPM’s I would suspect a weak compressor. I would like to see the high side reading a little higher (around 250) and the low side should be around 30psi.

  130. John :

    Date: June 18, 2011 @ 11:38 am

    Dennis, I have a 2000 Chrysler Town & Country with rear air. The system takes 46 oz of R-134A. The A/C was blowing warm air, I suspected the front expansion valve, so replaced it. After vacuuming the system, I have added 3 12oz cans so far. It is about 95 degrees out. The low side is reading about 70 psi, and the high side about 200 psi, yet still no cold air. Normally, I would think it the low side should be around 35 psi, and the system should start cooling, right? Bad compressor?

  131. dennisb - Auto Tool Sales :

    Date: June 18, 2011 @ 12:32 pm

    John, too high of a “low pressure” so that would make you think compressor, however the high side seems to indicate it is pumping as it should. If the system was fully charged, you would have higher than normal readings for both low and high sides. This makes me think that the cooling fans are not working properly or the vehicle’s engine temp is too hot – or both. Good Luck.

  132. Brian :

    Date: June 18, 2011 @ 1:21 pm

    Hi Dennis

    Thanks for the website will all the useful information!

    Like everyone else I have a question.

    I have a ’99 F350 7.3 4×4 Crew cab.

    The AC was just “OK” before I started fooling with it and took 20 minutes to really cool off the truck here in sunny Phoenix, it blew cold but I felt it should be colder.

    Upon the advice of a video series I made some changes (search youtube for “powerstrokehelp ac” and you’ll find the videos.

    I changed the orifice tube from a 38635 to a 38639, the 38360 is about .015″ smaller and actually recommended for climates that regularly exceed 105 degrees. While I was in there I replaced the accumulator. I pulled a -30Hg vac for 45 minutes, and recharged with 2.8lbs of R134a (I weighed an empty can and valve along with a full can and valve in order to get exactly 8.5oz out of the last can).

    At idle everything is fine, 35-40 on the low side and about 250 on the high side with 102 ambient outside temp, middle vent hovers around 50 degrees. At 1800 rpm (cruising RPM) the low side drops to 25 and the high side stays around 250-275 and the middle vent shows about 45 degrees.

    Out on the highway the compressor cycles on and off every 20 seconds or so while still blowing COLD. I ran a wire from the compressor switch to a test light in the cab so I could monitor compressor operation as I couldn’t hear it or feel it in the truck at highway speeds. My guess is that the air moving across the condenser is somehow causing the low side to drop past the 22psi threshold of the low side switch and causing it to cycle, but if that’s the case I have no idea why.

    I’m starting to think the orifice tube swap is the problem.


    Thanks for your time.

  133. John :

    Date: June 18, 2011 @ 1:59 pm

    Dennis, I added almost all of the last can of R-134A in the 2000 Chrysler T&C, so now I have approx 46 oz in the system. The pressures are now about 72 psi on the low side, and approx 260 psi on the high. I am getting a very small amount of cooling to the touch on the low pressure line, but not much. The cooling fans are working and the engine temp is in the normal range. It almost seems like there is a blockage of some sort in the system. I did change the compressor and dryer about a year ago due to compressor failure. Could there be residue in the system yet? The only thing that has not been changed are the condensor and evaporator (there are two evaporators – front & rear.) Any suggestions? Thanks for your help.

  134. dennisb - Auto Tool Sales :

    Date: June 18, 2011 @ 2:20 pm

    Brian, the smaller orifice tube is allowing less flow which equals lower pressure. If this is causing a problem, I would install the original one. Good Luck.

  135. dennisb - Auto Tool Sales :

    Date: June 18, 2011 @ 2:25 pm

    John, a blockage would result in too high of a high side and too low on low side since there would be reduced, or no flow. If I were checking it in person, I would check readings at different RPM’s, front and rear vent temps, line temps, condenser temp, etc. Good Luck.

  136. dennisb - Auto Tool Sales :

    Date: August 15, 2013 @ 4:50 pm

    Just opened comments back up on this article. Be sure to check out the 2nd page for gauge reading explanations. If asking questions (and cannot find the answer to your question in our AC articles) please provide as much info as possible. Thanks.

  137. Wilson :

    Date: August 19, 2013 @ 4:15 pm

    2002 Ford Crown Victoria – replaced accumulator and orifice when new compressor installed.
    Ambient temp. = 95℉
    Static: Low: 105, High: 105
    Idle: Low: 35, High: 275-Vent Temp:58℉
    1500: Low: 30, High: 310-Vent Temp:52℉

    Vent temp should be cooler…too much 134a? Bad compressor? Air/Moisture in system? (Pulled vacuum for 6+ hours and held at 30Hg for 2 hours after).

  138. dennisb - Auto Tool Sales :

    Date: August 19, 2013 @ 4:52 pm

    Looks about right actually with 95 degrees outside. The higher the outside (ambient) temp is the higher static and operating readings will be. You should know how much refrigerant was put in since the system was completely empty and on the vacuum pump for SIX hours? (15-30 minutes is the usual amount of time to keep on the vacuum pump.)

    I would expect maybe a little cooler vent temp with:

    1. Thermometer in the vent closest to the evaporator.
    2. AC set on max / recirculate and blowe speed on low.
    3. Running engine at 15-1800 RPM’s
    4. Max cooling achieved – Meaning the car was running long enough for the temperature not to be decreasing anymore.

  139. art barnes :

    Date: September 9, 2013 @ 9:47 am

    Hey, I have a 2000 3500 454. Yesterday I found a reading of 35 low and only 60 high but pretty good cold air blowing. The outside was 67 degrees. I just wanted to test my new cheap manifold gauges. Seems high side should be higher, about twice the temp, or 130 or so. Is this normal or perhaps my high side gauge is not reading correctly. Any thoughts, thanks so much!

  140. dennisb - Auto Tool Sales :

    Date: September 9, 2013 @ 10:43 am

    Art if you are really hooked to the high side, the reading should be 250 plus psi. So I would take the cheap set back and buy one of our gauge sets. :)

  141. Joe :

    Date: September 11, 2013 @ 1:02 am

    1986 Toyota Pickup, converted to R134a, very little cooling, just replaced expansion valve, still getting readings of 80 on the low side and 200 on the high side, I’m thinking compressor at this point. Your thoughts?

  142. dennisb - Auto Tool Sales :

    Date: September 11, 2013 @ 7:07 am

    Joe, could be the compressor but 200 psi is pumping pretty good. If the compressor is failing it usually will not be able to pump high enough pressure (200-300psi). The other thing could be that the expansion valve is not working properly. The expansion valve should be slowing the flow into the evaporator to a trickle. This creates low pressure (around 30psi on the low side is ideal at service port) and therefore cold temperature.

    Low Pressure = Cold.
    High Pressure = Hot.

    The other issue is that the expansion valve (on a 1986) was designed for use with R12 not 134A. So I would expect approximately 10-15% higher readings with the 134A, but 80psi on the low side is too high to achieve anywhere close to acceptable cooling. Good Luck.

  143. kelly :

    Date: September 18, 2013 @ 10:35 am

    hello, what causes horn of my honda accord 2000 model to work intermittently

  144. dennisb - Auto Tool Sales :

    Date: September 18, 2013 @ 11:07 am

    Kelly, the horn has nothing to do with the AC gauge readings that this article is about.

    But, normally when a horn “blows” by itself, the horn pad (aka horn switch or button) is faulty. The contacts touch completing the circuit just as if you pressed the horn yourself. Sometimes the switch (or horn contacts) can be changed without changing the entire airbag assembly in the steering wheel and sometimes it cannot. Good Luck

  145. kelly :

    Date: September 21, 2013 @ 2:12 pm

    Hello Dennis, its me again. I have this AC issue. My cars AC chills nicely in the mornings and evenings but only cools in the afternoons. Could low refrigerant be the culprit? By the way, I recently replaced the compressor and noticed this almost immediately.

  146. dennisb - Auto Tool Sales :

    Date: September 21, 2013 @ 3:47 pm

    Kelly, what are the low and high readings? Most likely low on refrigerant but I would see what the readings are to help diagnose. Good Luck.

  147. mike :

    Date: September 26, 2013 @ 5:08 pm

    2004 hyundai santa fe first time problem started blowing hot air noticed clutch on compressor not kicking in, added freon from local parts store cold air but noticed a bubbling around low line port schrader valve next day blew hot again, changed schrader valve topped off freon to 45 on low side blew fine but by the next afternoon was hot again got home to find a lime yellow/green oily spot on floor in garage. what do you think

  148. dennisb - Auto Tool Sales :

    Date: September 26, 2013 @ 5:16 pm

    Mike, it’s common to have a few bubbles from the schrader when you first disconnect. 45 is too high on low side, may of overcharged. The dye on the floor could have been from the actual leak or from the system relieving itself of the excess pressure if it was overcharged. I would clean everything, make sure at least 50 psi is in the system with it off (static pressure) and check for leaks using electronic leak detector and/or UV light. Good Luck.

  149. mike :

    Date: September 26, 2013 @ 5:47 pm

    thanks will try may get back to you soon

  150. mike :

    Date: September 26, 2013 @ 8:31 pm

    i checked around, under, and atop engine compartment where a/c lines and compressor lies…using black light found dye in the crease on the two piece housing of the compressor and nowhere else does this mean i may have overpressure the unit and now need to replace it

  151. dennisb - Auto Tool Sales :

    Date: September 27, 2013 @ 7:25 am

    You know there was a leak already, that’s why you added Freon. The dye on the seam of the AC compressor housing indicates a leak regardless of if you caused it or not, it should be replaced and the rest of the system checked (in case there’s more leaks). With an electronic leak detector you can check components that are hidden like the evaporator (and expansion valve) in the dash. You most likely didn’t cause a leak because there’s a pressure relief valve that will vent pressure if needed. Sometimes the pressure relief valve is located on the back of the compressor and also most systems will turn the compressor off when the pressures reach around 450 to 500psi on the high side. Good Luck.

  152. mike :

    Date: September 28, 2013 @ 8:32 am

    if no other leaks are found can i replace the compressor or do i need to replace expansion valve or other components….finances are tight. thanks for your help.

  153. dennisb - Auto Tool Sales :

    Date: September 28, 2013 @ 8:42 am

    Mike, some compressor warranties will require the expansion valve and dryer to be replaced. Some will only require just the dryer to be replaced. If I had my choice and the compressor just leaked like yours and didn’t “lock up” which could put trash in the system, I would replace the compressor and dryer and skip the expansion valve. Check with the parts store though to see what is required for the warranty. Good Luck.

  154. mike :

    Date: September 28, 2013 @ 8:58 am

    Do you know if the drier is easily accessible on the Santa Fe?

  155. dennisb - Auto Tool Sales :

    Date: September 28, 2013 @ 7:45 pm

    Mike, you may want to refer to a repair manual. Or just look at the physical location of the dryer.
    To others; just a reminder that DenLors Tools does sell quality Auto A/C Tools. Let us know if we can be of assistance.


  156. Freola :

    Date: February 28, 2014 @ 10:17 am

    Low side is 25psi and high side 180psi with AC on. When I turn the engine off I don’t hear the pressure equalizing in the oriffice area and low side reads 65psi and high reads 120psi. It should level its self to same pressure. Thanks.

  157. dennisb - Auto Tool Sales :

    Date: February 28, 2014 @ 11:01 am

    Yes the pressure will equalize but may take a little time. I would not be concerned as long as the AC is cooling well.

  158. hawthorne :

    Date: February 28, 2014 @ 5:31 pm

    Hi Dennis, I have a 2005 E55 MBenz with 65K mileage. I am having issues with the ac. Within two months I have refilled freon once. I am getting an alarm with the freon sniffer in the vent located in passenger side. When I attached the ac gauges the static pressure reads low side 35 high side 26. There is a manual switch to turn on/off the ac compressor. However the compressor is off all the time even if I switch to on, it will just blink. So I believe that the compressor does not turn on. With a static pressure of 35 on the low side, this should be able to turn on the compressor… but this is not happening. I also have to look for the leak. Thank you for your advise in advance. Hawthorne

  159. dennisb - Auto Tool Sales :

    Date: February 28, 2014 @ 5:52 pm

    Electronic AC leak detectors can have many false alarms. If there’s an indication it’s usually best to double check the possible leak by looking for oil or dye if possible. 35 psi is not normally enough static pressure to allow the compressor to come on. I would say at least 50 psi. You can tell if the compressor comes on by looking at the front clutch disc – it should be engaged and spinning if the electro-magnet (coil) comes on. Blinking could mean there’s other problems but based on the static pressure it could just be insufficient refrigerant. The system will not let the compressor run if there’s not enough because it gets lubrication form the oil that circulates with it. Good Luck.

  160. rasheed :

    Date: February 28, 2014 @ 8:54 pm

    Hello Dennis,
    My a/c temp at Max cool is 60 degrees at 80 degree ambient temp and at 1500 rpm my low side pressure is at 25 psi and high side is 250 psi. The problem that I am having is when my rpm drops around 1000 rpm, I get a vibration in my high pressure line from the compressor to condenser. what will cause a vibration like this?

  161. dennisb - Auto Tool Sales :

    Date: March 1, 2014 @ 8:22 am

    That’s not much of a temperature drop. The max air temp coming from the vents should be in the 50’s or possibly 40’s. Maybe the vibration is from air in the system. I know compressors can be a bit noisy if there’s air in the system which I suppose could cause vibration. I would have a shop recover, vacuum and recharge the system with the correct amount of refrigerant (adding oil if needed) and see how it reacts. Good Luck.

  162. seanw :

    Date: March 22, 2014 @ 8:53 pm

    How’s it going. I have purchased a 1990 chev 1500 with warm air. I have checked pressures and found low side around 40 psi and high side reaching 175. I am only getting about a 15 degree change in temp. All parts on the system appear to be new. Any help would be great thanks

  163. dennisb - Auto Tool Sales :

    Date: March 23, 2014 @ 9:19 am

    This time of year, the high in many parts of the country is around 70-75 degrees (South Carolina included). If you are checking the readings with that range of outside temp; at 15-2000 rpm’s, on max setting, blower speed on high. The compressor may not be pumping sufficiently. I would expect a low side of around 25 psi with such a low outside temperature. Good Luck.

  164. shawn :

    Date: April 18, 2014 @ 8:04 am

    I have a 2005 Jeep Liberty Sport. I had a leak in the ac condenser (you know the part that is in front of the radiator). Well I changed it put it all back together. So my question is when I put new freon in after changing the condenser how do I bleed out the air?

  165. dennisb - Auto Tool Sales :

    Date: April 18, 2014 @ 8:32 am

    The system needs to be pulled down into a vacuum with a vacuum pump. See the following article on Basic AC Gauge hook up.

  166. miguel :

    Date: April 26, 2014 @ 11:40 pm

    I had a problem with my 2003 Grand Cherokee, it stopped cooling and I did a service with a recovery machine to recover the refrigerant and I held on vacuum for 15 minutes. Then I recharged to the proper load and the dryer froze. The low side gauge was in vacuum and the high side was 130 ps.

    If you can help me I’d really appreciate that. Thanks.

  167. dennisb - Auto Tool Sales :

    Date: April 27, 2014 @ 9:07 am

    I would have checked the AC readings before deciding to remove, vacuum and recharge to see what the problem was to begin with. It’s common to have the dryer to get really cold and freeze a little during the refrigerant charge. It’s not normal on most systems for it to freeze up during regular operation (there are some exceptions). If you have the proper amount of refrigerant in the system, like you say and the low side is still in a vacuum, there’s most likely a stuck expansion valve. The 130 psi on the high side is probably an inaccurate reading because if the compressor is pumping the reading would be much higher.

  168. Alan :

    Date: April 27, 2014 @ 10:38 pm

    I’ve had a set of gauges for years. Used to use them for R-12. Can I use them for R-134?

  169. dennisb - Auto Tool Sales :

    Date: April 28, 2014 @ 6:28 am

    Alan, the 134A connections are different than R12. The thing keeping you from hooking up the R12 gauge set is the hose connections.  We sell a conversion kit FJC 6025 that screws right on to your R12 Manifold Gauge Set that allows hooking up to R134A. Also have the FJC6030 can tap for using the small refrigerant cans with the yellow hose.

  170. Mike P :

    Date: May 2, 2014 @ 5:44 pm

    Really need some help – my ac in my 2005 acura tsx was blowing warm so i put in some freon. The ac got a little cooler but immediately after the car started lagging while moving and there’s a grinding noise that in comparison sounds like the radiator fan rubbing against the shroud. It doesn’t do any of this before adding, and now the car runs normally only when the ac is off. I thought the problem might have been too much pressure so I used the ac as little as possible for the last few days. Today I went to a place that does oil changes and ac re charges. The guy bled the lines down to spec which I believe is 35 185 (when my buddy put the freon in it was reading 70 250 which I was told is very high) and put a pound of freon in. There was a ton of air in the lines which he bled out too. The ac now blows cold but it’s still doing the same thing and the compressor sounds like it’s ticking. I went back and told the guy it was doing the same thing but he doesn’t actually do mechanical work so he has no idea. Help! Why is the car lagging and making grinding noise even after the lines were bled of air and excess pressure? I’m afraid something else may be going on now. Thanks in advance for any help you could provide. -Mike

  171. dennisb - Auto Tool Sales :

    Date: May 3, 2014 @ 5:55 pm

    From what you’re describing the compressor is probably failing. The noise and the high reading on the low side is what indicates this. See our article on AC gauge readings for more information on what the readings should be. Good Luck.

  172. Drew :

    Date: May 13, 2014 @ 12:54 am

    Help! I have a car with a custom swapped engine, which utilizes the compressor from the swapped engine, and the stock condenser from the vehicle and modified lines. I cleaned out the lines and the condenser, changed the o-rings, purchased a new drier, changed the oil at the compressor, held it under vacuum for an hour, and charged it. First I charged it on a cold day, and the AC seemed to work good, but the next day when it was a little warmer, I turned the car on, the AC started to cool, but then I gave it a rev and it went warm! I drove it around and the same thing! Just today I rechecked the pressures and it was 30 psi on the low side at idle (it seemed to be cooling ever-so-slightly), so I added a little more freon and it bumped up to 40ish… it feels like it got a little worse… I revved it up and the high side pressures spiked to 500 PSI, so I shut it off. I know it’s possibly overcharged now, but even at 30 psi it wasn’t cooling… the only thing I can think of is I didn’t properly clean the condenser OR the lines on the high side are restricted – the AC shop didn’t do a stellar job on bending the lines and although when I cleaned the lines there was airflow (with compressed air), some of them visually look almost kinked – could that be the culprit? Thank you!

  173. dennisb - Auto Tool Sales :

    Date: May 13, 2014 @ 7:24 am

    Sounds like it is definitely over-charged now and the kinks in the lines could cause an issue. I would check to see if both vehicles (whatever you are working on and the donor vehicle, whatever that was) use the same type expansion valve or tube. I would consider the possibility of a partially blocked condenser especially if the lines were open on the donor vehicle. Another consideration, is that a few compressors have regulating valves built in depending on the application. Another cause of too high of readings would be from low airflow through the condenser cooling fins. In closing, after the above items are looked at and taken care of, I would diagnose the system normally by using the pressure readings to diagnose any other issues that remain. Good Luck.

  174. Drew :

    Date: May 14, 2014 @ 12:27 am

    Thank you so much! Another thing to add – even when I initially charged it to 30 psi, I had only used half of the amount of the amount of recommended refrigerant, and yet it showed normal temps. Fast-forward to today, I started the car and the pressures showed normal??? I gave the car a rev, pressures seemed to be okay, so I turned off the AC with the car running, then turned the AC back on and the high side spiked to 500 psi again! I also want to note that I heard a strange noise coming from the condenser area. I turned it off after the spike and pressures went down, so I tested it again, heard a noise from the condenser area and BOOM – the compressor overcharge valve gave out and refrigerant came out… so I DEFINITELY have an issue… have you heard of noises coming from the condenser before? I think I’ll just get a new condenser and have the high side lines redone and hopefully that fixes it. Thanks again for all your help!

  175. dennisb - Auto Tool Sales :

    Date: May 14, 2014 @ 6:33 am

    Such high pressures with half the charge doesn’t make any sense unless there’s no air cooling the condenser (fan inoperable). A new condenser will make noise too if the system has such high pressure. Good Luck.

  176. 02 impreza :

    Date: May 14, 2014 @ 9:07 pm

    I have an 02 Subaru Impreza WRX that I just recently replaced a low side line due to a hole. Vacuum was good and holding. Charged system, started car and the compressor was cycling with rpm’s but the gauges showed 150 high and 10 low. When I give it some rpm’s, the low side drops and the high side stays the same. Please help. Thanks.

  177. dennisb - Auto Tool Sales :

    Date: May 15, 2014 @ 6:58 am

    Based on the readings alone, LOW on BOTH high and low sides – seems to be under-charged.

  178. john :

    Date: May 15, 2014 @ 8:39 pm

    Dennis, Hi, I have a 2001 Montero Sport. The AC will work sometimes but not all the time. The pressure is good on high and low, 40-170. When I hit ac button the lite comes on. The compressor may or may not come on. Sometimes it will take several minutes or not at all. What triggers the relays? Thanks.

  179. dennisb - Auto Tool Sales :

    Date: May 16, 2014 @ 6:32 am

    I would check to see if there’s power and ground to the AC compressor’s clutch “coil”. It acts as an electromagnet engaging the clutch. Could be a weak coil or excessive air gap. If that’s not it I would get a wiring diagram from your specific vehicle. But whatever your problem is needs to be checked when the problem is occurring so you can verify what’s causing it. Good Luck.

  180. john :

    Date: May 16, 2014 @ 2:08 pm

    Dennis I’ve also noticed that when it works the engine revs up, but when the engine does not rev up the compressor and fan does not come on. Checked compressor and fan relays they are working, with relays out, I can hit the AC button, motor will rev up, plug in relays, everything works. But when I press the AC button and engine does not rev up and replace relays nothing happens. Your info is of great help, did not know a lot about how ac works after reading this info that you put out for others, I feel like I know a lot more about how AC systems work just got to figure this last problem out thanks. Also I can jump compressor terminals and fan terminals out and they work everytime, so would that mean ground and clutch is fine?

  181. dennisb - Auto Tool Sales :

    Date: May 16, 2014 @ 2:18 pm

    John, the problem needs to be checked when it’s occurring. You could jump power and ground to the compressor coil a hundred times, but if on the 101st time the clutch coil doesn’t engage the clutch plate, the AC won’t work. Whatever the issue is it’s always best to start testing when the problem is happening. Otherwise you’re chasing a ghost. Good Luck.

  182. nell :

    Date: May 17, 2014 @ 10:39 pm

    Dennis, my low side pressure was good and high also, it reads low: 25, high 200 and it blows cold air about 40deg. Everything was brand new installed, my problem was when I run my ac about 20 minutes my compressor was very hot to touch, I think my condenser works because its brand new including fan.

  183. dennisb - Auto Tool Sales :

    Date: May 18, 2014 @ 9:34 am

    Nell, don’t look for a problem if there is none. When a system is cooling like it should, that’s the best indication that there’s no problem. It’s normal for the compressor to become hot especially on the discharge side. As far as the temperature of the actual AC components to the touch or a safer way to test is checking with an infrared thermometer; Remember low pressure equals colder temps and high pressures equals hotter temps.

  184. Wave :

    Date: May 19, 2014 @ 2:56 pm

    I have a 91 Toyota Landcruiser. The ac works well at times. When I first start driving the ac works well for a time (anywhere from 10 minutes to 30 minutes) then the ac will start blowing warm air. I hooked up gages and when at idle an the ac working I have 35 psi low and 200 high. Then the ac will stop working. I noticed the low pressure actually went vacuum and the high still around 200 psi. Does this sound like a clogged expansion valve? If I replace the expansion valve will it normally stay clear or could it clog is a short time?

  185. Wave :

    Date: May 19, 2014 @ 3:02 pm

    On the above 91 toyota LC, I should mention the previous owner converted the system to R-134A.

  186. dennisb - Auto Tool Sales :

    Date: May 19, 2014 @ 3:11 pm

    Sounds like a bad expansion valve. I would replace the drier too if it’s older than two years. I would also look for a dirthy system whe the lines are off because contaminants from the old drier or from a worn compressor could cause the expansion valve to fail prematurely. Good Luck.

  187. Paul :

    Date: May 19, 2014 @ 6:57 pm

    Hello Dennis, First thanks for the site it has helped alot. I have a 2002 lincoln ls v8 that does not cool very well and does not stay cold. I had a shop a year ago tell me that my compressor was failing. The readings i am getting are at
    ambient temp – 68.8F
    Static High/Low side – 76 psi
    When i turn on the car and rev to 2k rpm the compressor will turn on and the pressure will start to climb from 30psi up to 65psi and the clutch will disengage. The high side on the other hand is at 110 psi when the clutch clicks on and drops down to 85psi when the clutch dissengages. The vent temperature fluctuates between 61-59 F. I know that the high side is not high enough and am wondering if there may be a clog in the condenser since the high slowly drops while the low pressure increases. I dont think that there is a leak in the system since i have performed these tests with the same results over a period of 2 months. Well thank you so much in advance and again love the site.

  188. dennisb - Auto Tool Sales :

    Date: May 19, 2014 @ 7:29 pm

    Paul sounds like the compressor is failing. It’s not pumping enough. If the condenser was clogged you would have really high readinds on the high side. Good Luck

  189. Paul :

    Date: May 19, 2014 @ 7:54 pm

    Thanks alot dennis you’re awesome!!!!!!

  190. Joe E. :

    Date: May 24, 2014 @ 3:29 pm

    Hi Dennis, I have a 1999 Toyota Solara V6. The compressor locked up on me.
    So, I replaced the compressor and Receiver/Drier. I evacuated the system for 1 1/2 hours (it held vacuum overnight). The I recharged the system using the manifold gauges. I had (3) 340 gm cans. Spec calls for 750-850 gms.
    I put approximately 2 1/2 cans (850 gm) or maybe a little more.

    Now, the AC is blowing nice cold air – temp at vent approx. 40F.
    However, Pressures on my gauges are:
    Low Side – Gauge pegged at 350 psi
    High Side – 220 psi

    Specs say Low should be 25-40 psi, High should be 225-250psi.

    I concerned about the high pressure on the low side. Also, getting squealing from the compressor clutch.

    Do you think I overcharged the system, or is there something else going on?

    Thank you in advance for your response.

  191. dennisb - Auto Tool Sales :

    Date: May 24, 2014 @ 6:44 pm

    Normally with a locked compressor, you’ll want to flush the system and replace the expansion valve and install the proper amount of oil (some compressors come with some oil in them and some don’t). Maybe you got lucky, time will tell. The 350psi on the low side is obviously incorrect (possibly a bad gauge). But, if it’s cooling to 40 degrees don’t look for a problem, that’s as good as it gets. The squealing at the compressor clutch is most likely not the clutch but a loose belt. I’d make sure it’s good and tight and recheck. Good Luck.

  192. Joe E. :

    Date: May 24, 2014 @ 10:17 pm

    Thank you, Dennis!
    I purchased the expansion valve, and attempted to get at it. But, on this car it’s behind the glove compartment, and it appears that you have to take most of the dashboard apart. I was afraid of disturbing the air bag, so I stopped at the point. I did not flush the system, but I did evacuate it. Hopefully, that’ll be good enough.
    I think you are correct about the belt not being tight enough. I also think you are probably correct about gauge being faulty.

    Thank you so much for your very prompt response. Now I’ll be able to sleep tonight. You da man!

  193. Joe E. :

    Date: May 24, 2014 @ 10:19 pm

    p.s. I did put the proper amount of oil in the new compressor.

    Thanks again!

  194. dennisb - Auto Tool Sales :

    Date: May 25, 2014 @ 8:29 am

    That’s good. A lot of people don’t know that you need to add oil for the compressor and the drier. And to turn the compressor shaft 10 times by hand before running the compressor. This helps prevent damage to the compressor since the compressor cannot compress the collected oil.

  195. dennisb - Auto Tool Sales :

    Date: May 25, 2014 @ 8:32 am

    Yeah the evaporator most likely has to come out to asscess the expansion valve. Have a great weekend and keep us in mind for your future automotive tool needs.

  196. Joe E. :

    Date: May 25, 2014 @ 1:23 pm

    Dennis – I am so impressed by your helpful attitude and expert knowledge! I will definitely consider buying any future tools and equipment from Denlors before any place else.
    In fact, the bad manifold gauge I used was a loaner from the auto parts store. So, I will be purchasing my own set, one that I can trust!
    I browsed through your online catalog and was amazed at the extensive list of items that you carry.
    I’m glad I found this site, and elated to know that there is a resource like you out there offering advice to the DIY mechanic.

    Keep up the great work!
    – Joe E.

  197. Steve :

    Date: June 4, 2014 @ 1:34 pm

    2004 Chevy Express 2500. 90% of the time when I start the van after it has been sitting after being run for awhile or such the a/c on it will blow warm air. I can hear and see the clutch engaging and disengaging. Once I start to move the vehicle at any speed it will start to cool down. For the life of me I can’t figure it out. Restricted condenser maybe?
    Ambient Temp: 84
    Static with no start for 2 days:
    Low: 85 High: 90
    Idle speed:
    Low: 27 High: 155
    Vent Temp: 44
    The AC started working as designed when I just started it. Engine has not been ran for a few days.
    Any help would be awesome!

  198. dennisb - Auto Tool Sales :

    Date: June 4, 2014 @ 2:24 pm

    I’d check the refrigerant charge because the high side seems very low. Also would check the readings when the problem is occuring. Good Luck.

  199. drhill :

    Date: June 6, 2014 @ 7:11 pm

    I have a 99 Navigator with rear AC. Just replaced compressor, condenser, orifice tube, expansion valve (for the rear AC), and flushed the system. I vacuumed the system, put the recomended oil and freon charge (62oz and 13 oz) and the ac does not blow cold. High side is 400, low side is 65 100 degrees ambient, 1500 rpm, recirc and max fan speed. vent temps 70 degrees. If I drive it, I can get it down close to 60 degrees from the vents. I sprayed water on the condenser and the temps and pressures dropped but very slowly. Clutch fan sucks a lot of air even at idle. I couldn’t get all of the oil out of the front evaporator, but I flushed it 3 times. any ideas? thx!!

  200. dennisb - Auto Tool Sales :

    Date: June 7, 2014 @ 10:02 am

    Based on the readings, seems like a little over-charged, which could be partially from the flush solution. When using flush sometimes it’s difficult to get it ALL out before proceeding. If some of the flush stays in it will reduce the cooling efficiency of the system. It may also cause other issues, but the most immediate affect is on the system’s cooling ability. The oil added is necessary especially after flushing and removing the oil that is already in the system. But here again if oil is already in the system and is not removed completely, you may end up with too much which can reduce the cooling ability of the system. The condenser is the most difficult to flush because of all of the tiny tubes that seem to be a mile long. So at least you didnt have that to flush since you replaced it. I would most likely remove the refrigerant with an AC recovery/recycle machine and pull a line to see if there seems to be too much oil. If so, I may try blowing the system out with compressed air if the system is over-run with oil to remove some. If the accumulator/dryer wasn’t changed, I’d replace it. I would then use an AC vacuum pump and vacuum the system down longer than normal in attempt to remove any remaining flush. Good Luck.

  201. matrix110 :

    Date: June 8, 2014 @ 2:09 pm

    I have a 2004 Pontiac Sunfire. Last year the air was working fine but kept getting warmer until no cool at all.

    Yesterday I tried a can of AC-Pro but could not get compressor to kick on until I installed a little freon but when I released the trigger the pressure gage went into the mid range of the red!

    I purchased a R134a gage set and checked the low & high side pressure this morning with AC & fan on max and engine running at 1k rpm. Low side was 60 psi and High side was 70 psi.

    When I turn off AC and back on the high side would jump to 100 psi then back to 70 psi. No change of the 60 psi on the low side.

    Compressor stays on and did not cycle off in the five minutes the ac was on.

    Could this still be a very low freon issue or something else?


  202. dennisb - Auto Tool Sales :

    Date: June 8, 2014 @ 3:46 pm

    If your gauge’s are reading correctly, looks like the compressor is not pumping. BTW, we sell professional quality AC Manifold Gauge Sets. The low side should go down to about 30psi and the high side should be around 250psi. If it was just low, the low side would go down to near vacuum and the high side would start to climb but would cycle on/off, indicating not enough refrigerant. Good Luck.

  203. drhill :

    Date: June 9, 2014 @ 9:44 pm

    Thanks for the tips on my 99 Navigator (my post was on 6/6/14). I did replace the accumulator as well. I did smell the flush after I opened the system up after recovering the freon the first time. I will leave it on vacuum a long time this time. How do I tell if there’s too much oil in the system by looking into a line? What should it look like? What would too much oil look like? I can easily open up the liquid line where the orifice tube goes or would you recommend another line? Thanks for the help!! Looks like I’ll be buying future tools from you now! :)

  204. dennisb - Auto Tool Sales :

    Date: June 10, 2014 @ 6:50 am

    If there’s excess oil in the system it may be pouring out once you disconnect a line. The accumulator/drier may be saturated with oil. Sometimes you may be able to blow some of the excess out or take it off and turn it upside down and rain some excess oil out. Some people don’t know that the replacement compressors will sometimes have oil in them already (most do). And therefore add too much oil. That along with not taking into account how much oil may still be remaining already in the system. I would always notice if a system appeared dry when I opened a system up or if oil would spew out freely when a line was removed. Either extreme is not good. So you have to use judgement along with knowing the specified amount of recomended oil to add for the system components being replaced. Not enough oil and the compressor may fail due to lack of oiling/lubrication. Too much oil and the concentration of refrigerant is lessened and the cooling efficiency will be reduced. Remember the refrigerant is what transfers the heat and cold in the system, not the oil. Also too much oil can harm the compressor because it can’t pump it as well when too much is pooled in excess.

    Just a reminder that venting (the act of just releasing the Freon into the atmosphere) is illegal and harmful to the ozone. The only proper way of removing the refrigerant is by the use of a recovery machine which can recycle the refrigerant. Most repair shops have this equipment. For everyone reading this, that may be posed with this decision – please, let’s try to take care of the planet for our future generations rather than saving a few bucks by venting.

  205. j :

    Date: June 11, 2014 @ 11:34 pm

    Help please….90 Mustang installed new compressor new oiler line new accumulator took to shop to be chargedhe tried charging twice said it won’t go past the oiler line said it goes through compressor through the hose through the accumulator through the firewall back out oiler line frost up and goes no farther

  206. dennisb - Auto Tool Sales :

    Date: June 12, 2014 @ 12:00 pm

    If there’s contamination from the old compressor failing, it can clog up the orifice tube which is usaully located in the inlet of the evaporator. The liquid line, which is what I think you mean when you say “oiler line” is the small diameter line that goes from the condenser to the evaporator. Some Ford’s have the orifice built-into that line and some, the orifice tube just is inserted into the inlet of the evaporator. Look for a clamp type mark that prevents the orifice from going further. So check the orifice tube. You should have already replaced it. But even if you did it could be clogged with trash from the old compressor. It should look like the one pictured below.
    Ford Orifice Tube

  207. Mattd :

    Date: June 13, 2014 @ 2:00 am

    Ac doesn’t blow cold. Hooked up to a gauge and it reads 300lbs in the red and wont move. What could be the problem?

  208. dennisb - Auto Tool Sales :

    Date: June 13, 2014 @ 7:27 am

    Sorry Matt, not enough information to go on. I’d check the high and low readings, check the condenser fan and go from there depending on what I found. Good Luck.

  209. Paul S. :

    Date: June 13, 2014 @ 10:33 pm

    2004 Toyota Corolla. Ac working great until about 1 week ago. While driving the air would be cold, then slowly warm up (30 secs), then continue blowing cold. It seems to keep doing this back and forth – maybe a few minutes of cold, then 30sec warm, followed by cold again. I bought a can of freon and added it to the car. Using the guage on the can it read a little low. I went though maybe 3/4 can and it still reads about the same. Not really sure if its over or under charged, but the cold, warm, cold cycle keeps happening. Any ideas where/what to look for or replace. Thanks!

  210. dennisb - Auto Tool Sales :

    Date: June 15, 2014 @ 4:37 pm

    I would start by checking the high and low readings…

  211. y2k :

    Date: June 17, 2014 @ 8:24 am

    Vehicle: 2000 Nissan Xterra

    Once vent temperature reaches 38-40 deg, compressor cuts out. When vent temperature goes up to 43-45 deg, compressor kicks back in.
    Pressures at idle: Low = 30-35 psi and High = 250 psi. Outside temp. = 93 deg.

    I am trying to figure out why the compressor is cycling when the vent temperature reaches the 40 deg mark.


  212. dennisb - Auto Tool Sales :

    Date: June 17, 2014 @ 9:01 am

    Seems like your car’s AC system working perfectly. Any cooler than that means the evaporator would be near (32 degrees) freezing, causing the system to have problems. Nothing needs to be done.

  213. y2k :

    Date: June 17, 2014 @ 9:31 am

    Thanks Dennis for the response.

    Would it harm the compressor/clutch if it cuts in and out constantly. With the recirculate on, it reaches 40 deg and almost every 2 minutes there is a cut-in/cut-out cycle.

  214. dennisb - Auto Tool Sales :

    Date: June 17, 2014 @ 9:41 am

    I see your concern. However, the system is designed to cycle, keeping the low side at around a 30 psi average. This also keeps the evaporator from freezing up. The cycle times will vary depending on what the outside temp is and what settings you have the controls adjusted to. There’s nothing you can do to change the way the system is designed to work. I wouldn’t be concerned as long as the air conditioning is working good, blowing cold air out of the vents. When a system blows cold air that is the best indication that it is working properly…

  215. Amopower :

    Date: June 17, 2014 @ 7:42 pm

    Hi Dennis – I am trying to find out once and for all whether the pressures should be checked at idle, or at 2000 RPM’s. I look thru all these posts and see people list idle pressures, and they are NOT scolded to re-measure at 2000rpm. Then I see other posts about making sure you have 2000 RPM’s. Even the P/T charts don’t seem to state one way or the other. When I measure at idle versus 2000 RPM’s there is a *significant* difference, enough to make me misdiagnosis. So once and for all – can you confirm that pressures should be measured at 2000 RPM’s? Thanks alot!

  216. dennisb - Auto Tool Sales :

    Date: June 18, 2014 @ 7:06 am

    Good point. I check at both, but as far as the pressure readings for diagnosis the readings you get at higher RPM’s are more accurate. If you have a weak compressor there usually is a lot bigger difference between idle and at 1500-2000 RPM’s. The compressor is turning much faster at the higher RPM’s so it pumps more even when the compressor is good and is functioning as it’s designed. On a worn compressor at idle it may not pump enough to cool well. At higher RPM’s it may be less noticeable that there’s a problem. So, when you are checking the readings record them at higher RPM’s usually 1500 – 2000 RPM’s is good. You can also check mechanical clutches to make sure it’s pulling a lot of air. If you have an electric cooling fan, it can be checked also. Good Luck.

  217. smokey :

    Date: June 18, 2014 @ 4:30 pm

    Hi Dennis: I have a 1994 Ford Explorer which the air condition was leaking freon but now has been repaired by an Automotive Air condition shop. My question is what should the Vent temperature read? Or what is the temperature range from the Vent? The ambient temperature is around 85 to 90 degrees and the output temperature from the vent is 60 degrees. Thank you

  218. dennisb - Auto Tool Sales :

    Date: June 18, 2014 @ 5:26 pm

    The vent temperature on the middle or right side vents, closer to the evaporator, should be cooler than 60 degrees when the ambient (outside) temp is 85-90 depending upon the settings. The control settings should be on Max (recirculate), the blower speed on low and the RPM’s 1500-2000. If checked at these optimum settings most cars will cool 40 to 50 degrees cooler than the outside temperature. Remember 32 degrees is freezing temperature and the system will not allow the evaporator to freeze, it will cycle the compressor off, so take that into consideration when using this rulle of thumb. So if your Ford doesn’t have a vent temp of 45-55 there could be a problem. Maybe low refrigerant or possibly a broken recirculate door. Black vehicles are also harder to cool because of the sun heating the cabin due to the darker color. I used to hate when customer’s had black vehicle’s and complained of the AC not being cool enough. There’s only so much I could do and changing the exterior color wasn’t one of them. Good Luck.

  219. Melo :

    Date: June 21, 2014 @ 8:12 pm

    Hi Dennis I have a 98 Rav 4 and my ac’s not cold. It’s fully charged with proper amount and had good vacuum. It’s not cold, even though the compressor clutch does stay engaged. But when you turn the ac on the low side gauge stays at 0 PSI and high side at 110 PSI, even if I raise the RPM’s to 2000 there’s no change.

  220. dennisb - Auto Tool Sales :

    Date: June 22, 2014 @ 8:54 am

    Inaccurate gauge reading. Even with the AC turned off, the static pressure should be more than zero. More like 80-100psi depending on the outside temperature. So, I’d say the gauge reading is not accurate for the low side. If the compressor is pumping the high side should be around 200-300 psi. The high side reading of 110 psi (if that’s an accurate reading) indicates it’s not pumping which means the compressor is bad. Good Luck.

  221. Les :

    Date: June 22, 2014 @ 8:54 am

    1972 Lemans Sport Pontiac
    Click the image for a larger view.
    I’m working on a 72′ Pontiac LeMans Sport of which I’m the original owner. I’ve replaced all major components and installed a new (not rebuilt) Sanden compressor in place of the A6 Harrison. I’m going back with R-12 and noticed after putting in 4 – 12 OZ cans that my low side reading is falling into the negative area (Vacuum). High side is only around 80 PSI. My thoughts are that the compressor is pulling against a restriction on low side area (TEX Valve, evaporator, Liquid side Receiver Dryer to TEX Valve. I realize the system needs 4 1/2 LBS of this liquid gold to operate properly but I was expecting the pressures to at least be positive on the low side and the high side to be above 125. Outside temperature at the time was 88 degrees. My thoughts are that I have a problem with the TEX Valve.
    I would like to get your option on this before proceeding further. Thanks

  222. dennisb - Auto Tool Sales :

    Date: June 22, 2014 @ 9:40 am

    Les, I think you’re on the right track. You’re only 8 oz away from a full charge, but with low side going negative I’d suspect the expansion valve also. Kinda surprised the expansion valve wouldn’t have been replaced during the compressor and dryer installation especially on such an old car. If there’s no cold air coming out of the vents at this point, I wouldn’t put the last 8 oz. in. Best to recover it and install the new expansion valve and dryer if you haven’t already. You could blow through other components like the evaporator and condenser when you have the system down just to make sure nothing else is restricted. Dryer desiccant can come apart in the dryer and clog components very quickly. Good Luck.

  223. Les :

    Date: June 22, 2014 @ 7:59 pm

    Thanks Dennis for getting back so quickly.

    The reason the TEX Valve was replaced was do to leakage coming from the pressure line going into the top cap where the diaphragm is located. I wasn’t counting on this valve going belly up, quality of parts vary as years past as you know. I did replace the dryer as part of the process with out a doubt it’s good practice as you know. I hope it didn’t come apart! I hadn’t thought about that!!

    Click for larger picture Click image for larger view.
    Thanks again for getting back with me and I’ll keep you informed on my progress.

  224. zzmike :

    Date: June 28, 2014 @ 9:51 am

    I have a 98 Mustang that wasn’t cooling well. Hooked up the gauges and found the high side was only going up to about 70. Charged up to 210 with low at 30. Worked fine for a couple of days, then quit cooling. Gauges showed high side low again. Evacuated system and vacuumed down to 30 inches. Shut off pump and left gauge open. Held vacuum for two hours with no leak down. Recharged with a small can of leak stop (which is 90% R-134a) and added additional R-134a until high side was up to 210 again. Worked well for 2 days then started warming up. Gauges show Freon low again. Is it possible that my compressor front seal is leaking during operation but won’t leak during vacuum test? Any other ideas on where the leak is? Leak stop had a dye and I can’t find any at any fittings. Thanks, zzmike

  225. dennisb - Auto Tool Sales :

    Date: June 28, 2014 @ 10:07 am

    Checking the gauges after using a vacuum pump, to see if there’s a loss of vacuum, is only one way to check to see if there’s a leak. I never relied on that very heavily. It’s not a real dependable test contrary to what you may have read. I only use that, as a quick preliminary check in case there was a huge leak (one that wouldn’t even hold Freon for a couple of days). I don’t recommend stop leak, it can cause other problems like stopping up condensers and expansion valves etc. It is also damaging to recovery and recycle machines. With that being said you obviously have a leak. It could be from the compressor seal while running as you said, but there would most likely be UV dye residue there. On a close visual inspection, if I don’t see dye I would consider the possibility of the evaporator leaking. It can’t be checked visually because it is in the dash concealed. On fast leaking evaporators, I’ve seen oil/dye in the drain tube of the evaporator. I’d use a good electronic leak detector and sniff the whole system paying close attention to the evaporator. A good place to check the evaporator is at the drain tube being careful not to wet the sensor of the electronic AC leak detector. Good Luck.

  226. Gene :

    Date: June 29, 2014 @ 12:35 am


    Been helping a family member with their AC Problem…. it would cool nicely for 2 or 3 days, then stop….obvious leak… put some dye in system, and never saw anywhere it was coming out…. then I used my “sniffer” to see what was going on…. I put the probe in the Evaporator “Box” and occasionally it would alarm….so I opened he firewall cover (Older Pontiac) and though I did not see any dye, I went ahead and replaced the Evaporator when I was is in there…evacuated the system and went to dinner…. an hour and a half later the gauges were at “0”…. Therefore, I got a “guaranteed” used compressor…evacuated again…. an hour later, gauges at “0” again….. the only thing I have not replaced now is the condenser, but I have seen no UV Die from anywhere on the condenser. BTW…even used different hoses on the manifold gauges in case there was a problem with the hoses…… still no luck and not holding pressures steady for an hour or so…… any ideas here….. OR maybe I’m relying on the gauges after evacuation too much? I have not filled with R134A since I did the evaporator, as not wanting to waste the expensive stuff….. should I go ahead and charge and see what happens??

  227. zzmike :

    Date: June 29, 2014 @ 7:20 am

    Thanks very much for your quick response. I’ll find someplace that has an electronic leak detector, do another charge and see what I can find. I’ll let you know what finally fixes it. zzmike

  228. dennisb - Auto Tool Sales :

    Date: June 29, 2014 @ 9:30 am

    Gene, sometimes leaks can be very hard to find. A zero reading on the gauge after letting it sit awhile after vacuuming the system down does indicate a leak. However, the leak could be somewhere from the gauge set or connections also. The leak would have to be large to make the gauge go to zero so quickly. Not that a refrigerant leak that takes only 2-3 days to affect the system isn’t large but it may not be enough to cause the gauge to go to zero so quickly. On older Pontiacs (and other GM’s) evaporators are not that common of a problem. Usually it’s the compressor, although anything’s possible. I wouldn’t try a used compressor. After the compressor sits awhile it’s much more likely to have dry seals that tend to leak after it’s put back into use (especially the front shaft seal). I’d put enough refrigerant in to get at least 50 psi and check the system with a good electronic leak detector. Don’t trust the leak detector every time it beeps even with a good one. Read the following if in the market for an excellent Freon leak detector. Good Luck

  229. Gene :

    Date: June 29, 2014 @ 11:51 pm

    Thank you, I worked on it this afternoon, and over a period of over 4 hours the gauge needle only decreased by just over a point or two, so I am unsure if it’s in the hoses, or the system.

  230. dennisb - Auto Tool Sales :

    Date: June 30, 2014 @ 7:08 am

    Exactly, could be either.

  231. Gene :

    Date: June 30, 2014 @ 10:25 pm

    Went ahead and charged system today…benn blowing at @ 42 degrees all day….. I will take a couple days and see what happens….

  232. doug :

    Date: July 1, 2014 @ 1:28 am

    Hi Dennis, thanks for your great article. I should have found it before I used the autozone r134a and low side hose/gage I borrowed from my bro in law….
    My 2008 Taurus was not very cold so I added the can of 134a and stopped when pressure was about 40 psi. I also noticed radiator fan got faster as it filled. When i was done, Ac didn’t work, so I vented some out and now ac is cold, but fan is really screaming! What should i do now? Leave it alone? Buy high and low pressure gages? Bring it to a pro? Thanks very much!

  233. dennisb - Auto Tool Sales :

    Date: July 1, 2014 @ 7:48 am

    Doug, thanks. But I really wish you wouldn’t let refrigerant vent into the atmosphere; it’s illegal to vent Freon into the atmosphere because it damages the Ozone. Refrigerant from our air conditioners escaping or being vented intentionally is the primary cause of our Ozone layer being diminished. Anyone needing to remove refrigerant because of an overcharge or to open a system up to be worked on, must (should) take the vehicle to a repair shop so it can be handled properly with a RRR (Recover Recycle & Recharge) machine. The refrigerant will be recovered, recycled and reused.

    I would check both high and low side readings. But at this point, if it’s cooling well, that’s one of the best indications that the system has the correct amount of refrigerant. With too little or too much Freon, the air conditioning will not function properly. The cooling fan works on different speeds as the high side pressure readings dictate. Unless you think the fan is excessively load like it may have a worn motor, I wouldn’t be concerned.

  234. Mms :

    Date: July 1, 2014 @ 3:51 pm

    Hi, I just changed evaporator and now radiator fan and compressor run continuously. Plz advise. I have corolla 2007

  235. dennisb - Auto Tool Sales :

    Date: July 1, 2014 @ 3:59 pm

    Changing an evaporator has nothing to do with the compressor and radiator fan staying on all the time. I would check each circuit separately using a wiring diagram for your specific vehicle. Keep in mind that the radiator fan will stay on if the temperature of the engine is high or if the high side reading for the AC is on the high end. The compressor may run even with the AC off to help remove moisture in the passenger compartment. Good Luck.

  236. Mms :

    Date: July 1, 2014 @ 4:15 pm

    Thanks for quick reply indeed. I want to say that the technician may have some connection with the problem during this evaporator fix, where he might of forgotten something. I talked to him but he doesn’t understand wiring very well. Before this repair the fan was turning on only when the ac needs it. Now it is turning on before starting. Appreciate your time and reply.

  237. dennisb - Auto Tool Sales :

    Date: July 2, 2014 @ 7:33 am

    OK, sometimes when there’s a poor connection or ground not properly made after doing a repair and having many connections undone. He should retrace his steps and make sure that ALL connections are plugged in all the way or ground screws are tight. Once I had a problem with the power seats not working properly after removing a dash and it ended up being an electrical plug that wasn’t plugged all the way into a module. Good Luck.

  238. bert :

    Date: July 2, 2014 @ 10:24 am

    Hi, I checked a 2001 Toyota Avalon yesterday, the AC clutch engages and the high pressure goes to 400 psi in 2 – 3 seconds then shuts the compressor off, I sprayed the condenser coil with a water hose and no drop in high pressure, I shut the car off and it holds the high pressure and does not drop for at least 10 minutes? No bubbles in the sight glass. Help


  239. dennisb - Auto Tool Sales :

    Date: July 2, 2014 @ 10:36 am

    Possibly over charged or a restriction in the system like a stuck expansion valve. I’d check the low side reading also and see what the static pressures are on both sides after the pressures equalize. Good Luck.

  240. Blue :

    Date: July 4, 2014 @ 2:23 am

    Borrowed my sons 2003 Chevy Trailblazer for a 4th of July Camping Trip. When he drops off the vehicle he lets me know the AC needs freon. I check and its blowing hot air. Too late, to have, it serviced the afternoon before I leave for my trip. So a go get some R134a, a fill gauge & tube set at my local autoparts store. But when I attempt to fill no freon will enter system. So I run over to HF & pick up
    a full gauge set. When I put it on I see ~50 psi on both hi & lo. With motor idling & AC on I see low side range from 45 down to 0 and high side goes to 75-100psi. Actually, low side sucks down to 0 in about 4-8 seconds when compressor kicks on & rises a bit slower to 45 after it kicks off. Hi side climbs to 100 as compressor runs & falls to 75 while its off. With engine at 2000 rpm it cycles faster and low side actually draws down to about -20 psi vacuum. But when I try to add freon, the system continues to cycle but no freon will flow in. I know I’ve got flow on low side gauge because I can see pressure cycling and I know I have freon flow into gauge because when I close valve at low side AC connection I can produce pressure in the inlet line by shaking the freon can. Is this symptomatic of a clogged orifice tube?

  241. dennisb - Auto Tool Sales :

    Date: July 4, 2014 @ 9:48 am

    I would say you probably have several issues. Low Freon is number one which means there’s most likely a leak. Since it’s not environmentally friendly to just add. I’d check for a leak with a leak detector. After any leaks are fixed I would vacuum the system down and add the proper amount of refrigerant (you could take a look at the orifice tube if it is equipped with one). After the correct system charge has been put in, I’d check both high and low readings. If the system is still going down into a vacuum there’s a restriction which could be a clogged orifice tube or a stuck expansion valve, whichever it has. If the high side doesn’t ever go up to at least 200 psi with a full charge the compressor is not pumping enough. Good Luck.

  242. 99 Ranger :

    Date: July 4, 2014 @ 5:32 pm

    Dennis: I am having issues with too much high side pressure, system kicks out on high pressure on ranger at 400-450 and the high side line is extremely HOT, low side seems fine 35-45. The system has been recovered and the compressor dryer and orifice tube replace ( the issue mentioned above was before repairs had been made ) After replacement of parts mentioned above, dropped in the recommended oil half in compressor and other half in dryer and pulled vacuum on system. Then dropped in recommended amount of r134a on ranger is 30 oz. when you start to get close to filling the system and it starts to cool a little the high side goes up again and causing the compressor kick off and on due to high pressure and the line is still very HOT. Had the system broken down again and had a feeling the condenser was a parallel and was stopped up I replaced condenser in front of radiator and started over again and lo and behold the same thing has happened. Im at a loss and im no AC expert but a average home mechanic working on his own vehicles. This issue is baffling to me and I don’t understand how i can have the same issue 3 times with new compressor, drier, orifice tube and condenser, note when I replaced major components the evaporator coil was flushed several times and blowed out with dried air for a while till all moisture was gone. This repair has costed me lots of money even a remanufactured compressor and aftermarket replacement parts also freon WOW, don’t know what else to do other than wishing i had taken it somewhere else to start with. This simple to moderate repair has been a major headache!!

  243. dennisb - Auto Tool Sales :

    Date: July 5, 2014 @ 10:09 am

    45 on the low side is high and you already know the high side is far above normal. Most of the time two things cause too high of pressure;

    1. The system is overcharged (with Freon, flush or oil).
    2. There’s not enough air through the condenser to cool it sufficiently.

    See the short article on “How to tell if an auto A/C compressor is faulty” for more details. Good Luck.

  244. Rick :

    Date: July 5, 2014 @ 10:39 pm

    My Question has to do with the gauge set,in one of your earlier comments you stated that when testing pressures the high side manifold valve should be closed, this seems to make no sense. Does that mean the high and low side pressure is reading from the low side valve? Could you elaborate on this? When I turned both sides on, the high side pressure pushed the low side gauge to max. It seems to me that the 2 sides of the manifold should be separate.

  245. dennisb - Auto Tool Sales :

    Date: July 6, 2014 @ 7:52 am

    Rick, both high and low valves should be closed when just checking the gauge readings. The manifold allows pressure from the vehicle to be measured. You only open BOTH valves when hooked to the vacuum pump. You typically only open the the low side valve when adding refrigerant. Opening both high and low with a charged system will allow the high side pressure over to the low side gauge as you’ve found out. Since the low side does not go up as high in pressure you may damage the gauge by pegging it out.

  246. Rick :

    Date: July 6, 2014 @ 9:27 pm

    Thanks Dennis thats what i needed to know, that explains it perfectly,thanks for your time

  247. Patrick :

    Date: July 7, 2014 @ 10:39 pm

    I just finished repairing system on 98 Rav4. I removed all components and flushed, cleaned debris from condensor and evaporator fins, replaced a sticking expansion valve, replaced drier, changed oil and added new R-134a. On a 100 degree day with the car running I’m getting gauge readings of low 35-40 and hi 180-210. The air temp at center vent on fresh air is 52 degrees. When referring to R-134a temperature pressure charts they say at 100 degrees low pressure should be 50-55 and hi pressure 315-325. I’m confused! My system seems to be cooling great! Can you give me your opinion on these numbers?

  248. dennisb - Auto Tool Sales :

    Date: July 8, 2014 @ 7:19 am

    The readings are normally higher with increased outside temperatures. It depends upon several things, one of which is how much air is being pulled through the condenser. It also depends upon how many RPM’s the engine is running at when you’re checking the readings. The low side readings are typically higher at idle compared to 1500 to 1800 RPM’s. That’s because the compressor (which is a pump) is turning faster, therefore pumping more, making the suction side (low side) readings lower. The best indication that the system is correctly charged, is that it is working properly. So if I were you, even though you may not understand all the actual readings compared to specs; I wouldn’t be concerned because the most important number is the vent temp, which is good.

  249. Chris :

    Date: July 8, 2014 @ 4:07 pm

    Dennis, thank you for providing your time and knowledge. It’s greatly appreciated.
    I just bought a 92 BMW 325i for my daughter’s first car and the ac is only blowing warm air (72-78 deg). It’s an R12 system and I have not tried adding any freon but here are my initial readings. Static pressure is 100-105 psi, low side pressure is at 35-40 with ac max and car idling but drops to 20-25 when at 1500-2000 rpm. High side is at 310-330 idling and will go up to 350 at 1500-2000 rpm. Here’s what puzzles me the most. The center vent temperature, with all other vents closed, will get down to 72 degrees. If I open all the vents, the temperature rises to 78 degrees. Is this normal? And what would you recommend that I do / check first? Again, thank you for your time.

  250. dennisb - Auto Tool Sales :

    Date: July 8, 2014 @ 4:30 pm

    Looks like it’s fully charged. Since you just bought it, it’s possible someone charged it with something other than pure R12 refrigerant. If need be , a shop can test it to identify the type of refrigerant. Not all shops have the refrigerant identifier tool, but should. First though, if the temperatures seem right on the AC lines (don’t burn yourself on the high side line). The suction should be cold and the discharge should be hot. This will very some depending upon where you check. It’s best to use an infrared digital thermometer for safety rather than physically touching all the lines. Basically, if the AC evaporator is getting in the 30’s you could have a door issue. Most likely the blend door. BMW’s aren’t always the easiest to work on, so it may take a tech to look into this further. As far as the vent temp being colder when all other vents are closed off that would be normal. But as you already know, 70’s is not cool enough.

  251. Patrick :

    Date: July 8, 2014 @ 4:57 pm

    Thanks for the assurance on the 98 rav4! I’m so glad I was able to ask a pro. I will quit worrying about the numbers since it is blowing ice cold!

  252. Frank :

    Date: July 8, 2014 @ 6:28 pm

    Our 2000 Yukon blowing hot air since late last summer after a successful charge last spring. Both high and low tubes are ambient temperature to touch. Borrowed a beat up Mastercool A/C Manifold Gauge Set recently from AutoZone but got zero readings on both sides. Tried to vacuum, nothing, no reading no movement. Any suggestions? Is it possible the systems open (massive leak) somewhere? Can’t tell from running it. Thanks.

  253. dennisb - Auto Tool Sales :

    Date: July 9, 2014 @ 8:26 am

    Frank, Mastercool is a good brand for AC equipment, but Autozone is likely as you said to have tools in very rough condition. It could be that the system has a very large leak or that the gauge set does. Either way, the Yukon surely has some sort of leak since you charged it and now the system appears to be empty. I’d add enough refrigerant to get to 50 psi and use a refrigerant leak detector. Be aware when starting to put it in in case there’s any loud hissing – there may be a large leak that does not require a leak detector. Keep in mind that some sound from the refrigerant entering is normal. Good Luck.

  254. Frank :

    Date: July 9, 2014 @ 7:42 pm

    I got another set of gauges that were known to work. The mastercool set was kind of fiddly, it registered on one of the other cars but not the Yukon. Pulled and held the vacuum overnight to 28 in hg. Added 3 oz stop leak with a dye but didn’t find anything leaking. Added 3 oz can pressurized PAG followed by 4 cans R134a. The clutch kept engaging disengaging as the 1st can was added while the pressure rose and fell with the clutch activity. The other cans added easily and was done around 55 psi. Will watch for the leaks but the dye is very easy to see as it left a trace on the port and equipment when it was done. Anything to else to watch for? The loss of cooling last year was abrupt but the charge early today seems to be holding.

  255. dennisb - Auto Tool Sales :

    Date: July 9, 2014 @ 7:48 pm

    Stop leak may cause issues. The stop leak may slow the leak down, or maybe not depending upon where the leak is. Stop leak may also damage the compressor, clog up the condenser, evaporator and/or the expansion valve. If taken to a repair shop and the shop finds out that there’s stop leak in the system – they most likely will refuse to work on it. Stop leak damages (stops up) expensive recovery units. In fact we sell a filter to help prevent damage to AC refrigerant recovery machines because stop leak is such a big problem for shops that service A/C. Good Luck.

  256. Jarvis :

    Date: July 10, 2014 @ 12:29 am

    Have a 1996 Acura Integra. Air blows very cold till the car gets to about 60 mph. Once at that spend it shuts down. Can’t figure out what would be causing this problem.

  257. dennisb - Auto Tool Sales :

    Date: July 10, 2014 @ 7:24 am

    Jarvis, I’d start with checking pressures. However, it is normal for the AC to turn off during hard acceleration and turn back on after the throttle has leveled off. Good Luck.

  258. Jarvis :

    Date: July 10, 2014 @ 8:30 am

    Pressure are good. Compressor is cycling as it should. Like I said once I get to highway speeds it shuts down. I completely lose my A/C on the interstate.

  259. dennisb - Auto Tool Sales :

    Date: July 10, 2014 @ 8:53 am

    I’ll take your word for the readings and correct compressor cycling. I would notice the RPMs over 60 MPH in case WOT (Wide Open Throttle) parameters may be shutting the AC off. Also if the engine’s temp is too high the computer will turn the AC off. Funny how some people (not saying you) will notice if they are hot but not if their engine is. Also, if the AC evaporator ices up the A/C will not work either. May take some diagnosis from someone with knowledge and experience in person to figure out the problem. Good Luck.

  260. Aaron Rogers :

    Date: July 13, 2014 @ 3:51 pm

    I was putting freon in my 2004 Honda accord. It was blowing cold just not as cold as it use to & I accidentally put too much and it started coming out of the hose down low. I unhooked it then I let some of the freon out. Now the compressor kicks on for like 2 seconds then kicks off for awhile. My ac is blowing hot. No cold air at all. Does anyone know what could be wrong??

  261. dennisb - Auto Tool Sales :

    Date: July 13, 2014 @ 4:13 pm

    Aaron, more is not always better. It’s easy to overcharge because some systems don’t hold much to begin with (some just a little over a pound). Overcharging causes excess pressure to be discharged out the pressure relief valve (that is if it doesn’t create a leak). Refrigerant released into the atmosphere damages our Ozone. I recommend you take the car to a qualified technician that can recover what’s left of the refrigerant, vacuum your system down and charge it properly with the correct amount. They can tell you if you caused more problems or not and if anything else is wrong. AC not cooling is not always caused from low refrigerant. Sometimes other things can make the AC blow hot. Good Luck.

  262. MikeC :

    Date: July 15, 2014 @ 4:23 pm

    I have a 2000 Bonneville that’s blowing cool air. Gauges read 30 on low side and high side bounces between 100 and 105. I’m assuming main problem is just low freon, but is it normal for high side to bounce? It’s almost like watching the second hand on a watch with it constantly bouncing every second. Thanks

  263. dennisb - Auto Tool Sales :

    Date: July 15, 2014 @ 5:21 pm

    I wouldn’t be too concerned about the high side AC gauge needle bouncing when checking your car’s A/C. Many times it’s normal depending on the model, the quality of the manifold AC gauge set and the severity of the bounce. I’d be more concerned with getting the correct charge in the system and what the temperature is coming out of the vents. Good Luck.

  264. John :

    Date: July 15, 2014 @ 9:09 pm

    Thanks Dennis for your time and help.
    My car retrofit from R12 to r134a but kept same tube and fin condenser but stronger fan. At ambient between 80-95, 850RPM low side is 50-55, high side is 170, center vent 57F. As soon as I rev the engine above 1000, low side will come down to 30., at 1500- 2000, low side is 20, high side still 170 vent 44F. I know for a fact that the system is undercharged. I did a good vacuum and let it take in as much as it could while system off, then added an ounce more. This is originally a 2.4lb system. what bothers me is I can’t get the low side lower than 50 at idle even after replacing the expansion valve. Its a big car, so its a little uncomfortable at high ambient and while stop and go to keep it cool. the evaporator inlet and outlet temps are very close and I don’t think adding more refrigerant would help, what do you think ? will upgrading my condenser help in any way ?

  265. dennisb - Auto Tool Sales :

    Date: July 16, 2014 @ 7:19 am

    John, retrofitted AC systems on cars can be troublesome to diagnose properly because the system obviously was not designed to use 134A. Typically you’d see higher over-all readings after to switching to 134A and that’s why a better condenser fan is a good idea. But that’s not what you have exactly. Low refrigerant is the common cause of the AC not blowing warm. However, the low side reading you have at 50-55 at around idle is too high while the high side is too low. This is an indication that the compressor is not pumping good enough, especially since you say it is undercharged. When you raise the idle the compressor is turning faster which means it’s pumping more volume of refrigerant like it needs to work properly. The variable that can throw this diagnosis off, is the fact that you don’t have the refrigerant in the system that it’s designed to use. But typically, 134A pressure readings are higher than R12 and we aren’t seeing that with your high side reading. So, I would be leaning toward replacing the compressor. Since this is a retrofit though, I would check with a classic auto AC parts company to see if there’s a retrofit expansion valve that can be obtained for your specific year, make and model. If there’s a retrofit expansion valve available for 134A, the low side reading may come down and you may be able to fully charge the system and get into the correct zone of pressure readings for both high and low sides, even at idle. And as far as replacing the condenser… I don’t think that would help your low side reading, at idle, at all. You could check the gauge readings after you’re able to get a full charge in the system though, if the vent temp is still not where it should be. Good Luck.

  266. nissath :

    Date: July 16, 2014 @ 4:43 pm

    So I believed I may have over charged mine in my car. How would I bleed it safely?

  267. dennisb - Auto Tool Sales :

    Date: July 16, 2014 @ 5:00 pm

    An AC recovery and recycle machine. Releasing into the atmosphere is illegal and damaging to the Earth’s Ozone. I recommend you take the car to a qualified technician that can recover what’s left of the refrigerant, vacuum your system down and charge it properly with the correct amount.

  268. John :

    Date: July 17, 2014 @ 11:06 am

    Dennis, I thank you sincerely for your suggestion. It makes since that the compressor could be on the weak side. Thanks again.

  269. adriano666 :

    Date: July 17, 2014 @ 12:39 pm

    Is normal that my a/c car temperature at first speed of fan is about 44°f driving or idle, and when I increase the fan speed temperature goes up to 60-62° along with every speed of the fan( as fast as it blow temperature get less cold) any ideas or advices?! Thank you!

  270. masrepus :

    Date: July 17, 2014 @ 4:27 pm

    What does it mean if the recharge kit is showing the low side pressure at 150 – the max value in the gauge?

    Odyssey 2007. AC was blowing hot air so I hooked up a recharge kit. Right off the bat the gauge is reading at 150 so I did not add any. The compressor is not engaging either. Instructions say to use half a can to get the compressor to engage, but also not to overcharge.

  271. dennisb - Auto Tool Sales :

    Date: July 17, 2014 @ 5:42 pm

    I’d go by readings from a good quality AC manifold gauge set (like the ones we sell) checking both high and low readings. If your system was working and stopped; and there’s been no Freon added I’d suspect that the 150 psi is incorrect. Static pressure should be 80-100 psi on a full system. If you find that your readings are within that range, that’s an indication that it’s not a low refrigerant problem to begin with. But dependable readings will need to be gauged before proceeding, Good Luck.

  272. dennisb - Auto Tool Sales :

    Date: July 18, 2014 @ 7:22 am

    adriano666, that is normal operation. The lower the speed, the colder the air. The faster the speed the warmer the air. Make sure the settings are on recirculate (max) for the coldest air. If you feel that the air could be colder, I’d check both high and low gauge readings. Good Luck.

  273. rex647 :

    Date: July 18, 2014 @ 3:09 pm

    1984 5.3lt jaguar xjs
    I have converted the system to 134 I have changed the compressor (heavy Harrison) drier regulator and the evaporator is brand new, it has no leaks, I had it recharged today and the temp is not cold cold,
    its just bit colder than no gas was. I have a low side gauge and without the engine running the pressure is 150 psi. Is this too high for low side? I will check with the aircon on full tomorrow and engine running. But I don’t want to do the compressor in, if the low side is to high pressure.

  274. dennisb - Auto Tool Sales :

    Date: July 18, 2014 @ 3:32 pm

    Static pressure (reading with the AC not running) should be 80-100 psi on a full system. It’s possible you have an incorrect reading especially if the system was not overcharged. Good Luck.

  275. Blue :

    Date: July 19, 2014 @ 1:59 am

    Hi Dennis! I posted a question here back around July 3 or 4 regarding my system not taking freon when charge it was exhibiting pressures & cycling indicating it was low on freon. I suspected I had a clogged orifice tube but I just wanted to let you & others know the turned out being with the cheap freon charge kit I bought. I bought a can valve (the manifold set I bought at HF didn’t come with one) and as soon as I hook up a can to the charge hose on the manifold and opened the low side manifold valve the system took the charge without a problem. Still can’t figure out what was wrong with the cheap charge kit since I had pressure communication separately from the can valve to the gauge and from the gauge to the low side inlet valve. Go figure! Thanks anyway.

  276. Harrie :

    Date: July 22, 2014 @ 10:40 am

    Hi Dennis I wanna post a question and I hope you can help me. I have here a Voyager 2.8 crd 2007. The high pressure side is going to 20 bar and the low side is 3 bar. I concluded that 1 of the two fans is not working at the high speed. Now I have the question do you know that problem?

  277. dennisb - Auto Tool Sales :

    Date: July 22, 2014 @ 11:44 am

    Harrie, I don’t know what the BAR readings are. I would need the PSI readings. It may not be necessary for both fans to be on (or at high speed).

  278. alex :

    Date: July 22, 2014 @ 7:11 pm

    Got a question for you Dennis perhaps can help out. I have a 1995 civic and recently replaced a compressor and dryer and recharged DIY style using manifold and weight of r134a.

    Still not blowing to cold after about a month of it being installed.

    Taking static reading is 90L/90H. When rev up it was 80/400.. Hear the compressor cycling on/off… Notice condenser fan not starting and not cool.. Thinking this was expansion valve issue? Was working for some time- think perhaps this blocked?

  279. dennisb - Auto Tool Sales :

    Date: July 23, 2014 @ 7:10 am

    Alex, the condenser fan not starting is what I’d be checking. Without proper airflow through the condenser the readings will be too high (like you have). Also (not sure if you used a vacuum pump before charging) if you didn’t use a vacuum pump you’re gonna have a lot of air in the system which will alter readings and decline efficiency.

  280. Gary farley :

    Date: July 23, 2014 @ 12:56 pm

    2006 envoy a/c works fine while moving. Running at idle for few minutes starts blowing warm, not hot.
    Bought autozone cheap refill kit wit gauge and saw that my system seems to be way over charged. Needle half way in red. Car was not running at the time
    Is there a drain? Should car and ac be running?
    Need advice.
    Thank you

  281. dennisb - Auto Tool Sales :

    Date: July 23, 2014 @ 2:01 pm

    Gary, working with refrigerant can be dangerous. Letting refrigerant loose into the atmosphere harms the Ozone and is illegal. Take the Autozone gauge back if possible, since it is practically worthless. High and low gauge readings from an AC Manifold Gauge Set, are needed to properly diagnose an AC system. Be sure to see the second page of this article if you haven’t seen it already. The system is not likely overcharged unless you overfilled it. If the AC works properly going down the road, the most likely cause of the AC not cooling while at a stop is the cooling fan not working as it should. Good Luck.

  282. rex647 :

    Date: July 23, 2014 @ 2:38 pm

    found the problem. its not cold because all the copper wire cold transfer windings inside the fuel cooler have worked loose and are moving with the flow of the 134 or suck of the compressor and blocking up the cooler to compressor pipe.

  283. Stephen SMITH :

    Date: July 25, 2014 @ 7:02 pm

    I just changed a/c compressor, dryer and orifice tube along with all o-rings charged system worked great for a week now at 1300 rpm my compressor cuts off and high side stays at 285-290 and low side goes from 30-19 could it be orifice tube clogged?

  284. dennisb - Auto Tool Sales :

    Date: July 26, 2014 @ 9:49 am

    If the old compressor was locked up or very noisy, there could be contaminants in the system that would possibly collect at the orifice tube. So it could be partially clogged. The readings aren’t that far off, so I will assume that the AC vent temperature is not cold when the engine is at 1300 RPM’s (if it’s cooling well I wouldn’t be concerned with the cycling). If it’s not cooling well, I’d make sure the cooling fan for the condenser is operating properly. Also keep in mind that when RPM’s are raised to a certain point it’s normal for the compressor to go off. I would think that 1300 RPM’s is not high enough for this to occur but higher RPM’s could be. Not sure what type of vehicle you have. But 4 cyl engines are quicker to turn the compressor off during what’s considered WOT (Wide Open Throttle). Good Luck.

  285. Jerry bloomer :

    Date: July 26, 2014 @ 12:08 pm

    When you say normal readings on low and high side I didn’t see what the ambient temperature was. I’m in Phoenix and its 105. Now what’s normal?

  286. dennisb - Auto Tool Sales :

    Date: July 26, 2014 @ 12:52 pm

    The 105 degrees outside is the ambient temperature. Both high and low readings will be higher when the outside temperature (ambient) is higher. So I would say normal could be around 40 low and around 400 high side. The system will always try to maintain around 30 on the low side if possible.

  287. Anthony :

    Date: July 29, 2014 @ 3:33 pm

    Hi Dennis,

    Great article with useful info! I have a 2005 Audi A6 3.2Q, that’s been having a/c issues off and on. A/C would blow cold then suddenly hot, and now just hot. I replaced a bad pressure/temp sensor and the o ring, and lost all the r134 in the process. We hooked up a vacuum on the low pressure port for just over and hour and it held -30inHg. We then tried to refill the system with a few cans from autozone but it wouldn’t take. Car was running with the a/c on max blower and max cold. Compressor never kicks on, but I’ve read that it won’t with low refrigerant. System only took in about 100g, and no more. A buddy of mine mentioned that we have to vacuum both the high and low pressure ports. Is this what we’re missing? Thanks for any help!


  288. augie :

    Date: July 29, 2014 @ 10:45 pm

    I replaced my cut off switch for the A/C. I evacuated and filled back up the gauges. Low was good but high side is way too low. It does blow cold air. What would cause this?

  289. dennisb - Auto Tool Sales :

    Date: July 30, 2014 @ 7:15 am

    First, for the benefit of others reading this (and our Ozone) PLEASE have refrigerant recovered properly so it can be recycled instead of being released into our atmosphere when opening up a system for service. The system may not need to be opened to make some repairs. Sometimes the problem could just be electrical, so a second opinion may be worth a trip to the shop anyway.

    Anthony, 100g is only 3.5 ounces. But lets back up. You asked about applying vacuum to both low and high sides. The AC gauge set would be hooked to both service ports before hooking up the yellow hose and applying vacuum. See our “Car A/C Vacuum Pump Faq’s repair article” for more details on how to properly pull a vacuum down before charging.

    However, using the vacuum pump improperly, would not be the cause of the Freon not going in. Ever wonder how shops can put refrigerant in without the car running? AC machines use an internal pump to put Freon in a car’s system. A long time ago at a Goodyear store in the 1980’s, I used an old charging station that used a heat blanket that went around the 30 pound container to heat the refrigerant to assist in charging a car’s AC system. These two methods don’t require the car’s engine (or compressor) to be running. But, when you are charging a system with small cans and no special charging station, the vehicle’s compressor is required to come on. After you add some refrigerant, like you did, the pressure will be enough for the compressor to start to come on. The suction (low) side will start to draw the refrigerant in. The compressor will normally cycle on/off rapidly at first until the charge is increased, staying on longer as you come closer to a complete charge. It’s normal for cycling to occur after the complete charge also, to maintain a proper target reading of approximately 30-35 psi on the low side, which prevents evaporator freeze-up.

    Seems to me the main problem with your car was electrical to begin with. The compressor wasn’t coming on before and is not coming on now, to be able to complete the charge. I would check to the low pressure switch and the compressor clutch coil. There could be many other possible failures but these are the things I would start with.

    The original problem you had still exists. The compressor is not coming on. Except for now you haven’t got much refrigerant in the system. After the electrical issue is resolved the system will capable of accepting a charge (with the compressor operating normally). Good Luck.

  290. dennisb - Auto Tool Sales :

    Date: July 30, 2014 @ 7:36 am

    Augie, If you have accurate readings (you don’t say what the readings are) and the high side is too low; And you have a full charge, the compressor may be faulty and not pumping sufficiently. Good Luck.

  291. William Lai :

    Date: July 30, 2014 @ 9:29 am

    I just evacuated my AC system in a workshop. And then when recharging the gas to my AC system, the senior mechanic charged the high pressure line first before the low one. Is this correct that he did it like that? Now my car is blowing sometimes cold sometimes warmer air. Please help me.

  292. dennisb - Auto Tool Sales :

    Date: July 30, 2014 @ 9:50 am

    William if using an AC machine with the engine OFF, it doesn’t matter if it’s charged through the low or high side. If running the car, only the low side service port should be used to charge the system. Since your air con is still not working properly, I would check low and high side readings and go from there. Good Luck.

  293. joey729 :

    Date: July 30, 2014 @ 12:21 pm

    I am sorry the reading were 40/45 would a faulty bcm or pcm cause that? and is it normal for the clutch to stay on while the ac is on without stopping?

  294. dennisb - Auto Tool Sales :

    Date: July 30, 2014 @ 12:40 pm

    Not sure what you’re sorry about, I don’t see any previous post from you here. Joey if 40 is the low side it sounds too high (high side reading not provided). The BCM or PCM has nothing to do with the pressure readings. The AC clutch should cycle.
    It is normal however, for the AC to be on sometimes even when the AC is turned off. The AC helps the climate control system to remove moisture from the passenger compartment, even when the AC is not needed. For instance the compressor may run some in the winter time when you’re using primarily heat. This helps remove moisture so your windows don’t fog up as easily. Good Luck.

  295. joey729 :

    Date: July 30, 2014 @ 1:43 pm

    No i said the high side was only 45 so 40 on low is too high I onle added 2 12 oz cans which is slightyl under of the capacity of 1.35 pounds i did not want too over fill it and low side went too 40 that is why i stopped after 2 can

  296. dennisb - Auto Tool Sales :

    Date: July 30, 2014 @ 2:00 pm

    If the compressor is running, 40 on the low side is too high, but if it’s not running you can’t go by that. If you are getting only 45 psi on the high side I would not trust your gauge readings. Static pressure would be more than that.

  297. joey729 :

    Date: July 31, 2014 @ 3:17 am

    yes its 40 low and 45 high side only thing i replaced was the high side valve static pressure was 50/50 without car running with car running it is 40/45

  298. dennisb - Auto Tool Sales :

    Date: July 31, 2014 @ 7:09 am

    Static pressure should be 80-100 psi on a system that’s fully charged. However, seems like the compressor is not pumping sufficiently. Anytime the compressor is running and the readings barely change, this indicates the compressor is not doing it’s job. When the clutch engages, the low side should immediately start to go lower and the high side should go higher. If it’s not the compressor is not pumping enough.

  299. ShawnS :

    Date: August 7, 2014 @ 11:10 pm

    I have an Olds Intrigue which I have been diagnosing.. At first the system wouldn’t kick the compressor in when adding Freon, so I vacuumed it down both sides for which reached -32? didn’t think it could reach past -30.. Anyhow the issue is.. I would add freon back in and the low side never idles past 20-23psi and the high side will continue to rise as I put more in 275 and climbing (as I put more in..) but the low just remains at 20-22psi after shutting valve off from adding freon. This car is equipped with drier on ac hose assembly right off the compressor, orifice tube, and a Accumulator. It does blow cold air out of vent but not cold enough to be within 42-55 after hitting High side of 320psi and this is after adding 36oz of freon.

  300. dennisb - Auto Tool Sales :

    Date: August 8, 2014 @ 6:38 am

    The fact that your vacuum reading went down past the maximum reading of 30, tells me that I would not trust the gauge set you have (at least the low side gauge in particular). Same goes for the low side pressure reading when the vehicle is running. The static reading should be between 80-100 psi with vehicle turned off. The correct amount of refrigerant should have been installed since you had the system completely empty at one point. Hopefullly that was the 36 oz. After an accurate gauge reading is obtained I would go from there. Good Luck.
    134A Low Guage Vacuum Reading

  301. ShawnS :

    Date: August 8, 2014 @ 10:44 am

    I have done a psi check this morning @ 70 degrees.. Low reads 85psi and high reads 80-85psi, needle was between the 2 marks that are increments of 5 and this was just sittin still not running.

  302. dennisb - Auto Tool Sales :

    Date: August 8, 2014 @ 10:59 am

    Going by the static readings you’ve given appaears to be a full cahrge.

  303. eliseo :

    Date: August 14, 2014 @ 9:17 am

    I have an ac problem that I ran into. The compressor engages for about 2 seconds. The low side drops to about 25psi but high side stays the same at 100 psi. Could it be a switch or something else? The expansion valve has been replaced, receiver drier replaced, compressor has been replaced. Am I just over-thinking this?

  304. dennisb - Auto Tool Sales :

    Date: August 14, 2014 @ 10:48 am

    Not sure why all the parts were replaced or what type of vehicle you’re working on. But I’d check the static readings first. It’s possible the refrigerant level is too low. If the static readings are between 80-100 (which, by rule of thumb indicates a full system) I would check the high side gauge integrity. It should be moving when the low side drops to 25. Good Luck.

  305. Juan :

    Date: August 14, 2014 @ 11:06 pm

    My a/c sometimes blow air cold and sometimes hot air

  306. dennisb - Auto Tool Sales :

    Date: August 15, 2014 @ 10:07 am

    Juan, that’s not enough information for me to go on. You may want to get some readings and go from there. Good Luck.

  307. Mark :

    Date: August 16, 2014 @ 8:01 pm

    1996 Ford Explorer (with “Climate Control” system). Compressor and orifice tube was replaced last year, as compressor was seized. Charged with the recommended amount of R134a, worked fine until last month. Acted like low freon, and suction PSI was high (55 PSI) on 90 degree day. Added 12 ounces R134a last week, worked OK, not great, suction PSI dropped to 47 when running. Now vent air is about 60 degrees at best (usually warmer) and suction pressure is near 70 PSI. No leaks apparent anywhere. (Very clean under hood!) Could a loose orifice tube act like this? Or…?

  308. dennisb - Auto Tool Sales :

    Date: August 17, 2014 @ 9:35 am

    Mark, most likely the compressor isn’t pumping sufficiently. We don’t have the benefit of both readings to go by, but your initial 55 psi is high. Which indicates to me that you should not have added refrigerant. After adding though, the system is most likely overcharged. I would have the refrigerant recovered, change the orifice tube, charge the system with the specified amount of Freon, check both high and low readings; then go from there. If the low side is still too high, the compressor is failing. It’s common to have a replacement compressor fail especially after a seized compressor has contaminated the system. Anyway with the correct charge – and going by the high and low readings the system can be properly diagnosed. Good Luck.

  309. lea :

    Date: August 18, 2014 @ 9:08 pm

    Thanks for helping. I have a 1994 Maxda B-4000 that was changed over to 134a about 4 years ago. About a year ago it quit working and I just lived with it. Gave it to my grandson and wanted to get it fixed for him. Carried it to Firestone and they said the hoses were leaking. Ordered new hoses, pulled them and flushed the system until all I got was clear liquid. Installed them, replaced all o-rings, and the dryer and the orifice tube. Pulled it down to -29 lbs. by vacum pump running 2 hrs. Let it sit for an hour and it held that number. Put 2 1/2 cans in and tried it out. Gauges read 44 low, 250 high and it is only cool (60 degrees out the vent). Help…..

  310. dennisb - Auto Tool Sales :

    Date: August 19, 2014 @ 9:00 am

    Lea, there’s no reason to flush the suystem when just chaning hoses. Whenever you do flush a system it’s important to get all of it out before charging. Sounds simple but the flush can become trapped in certain places and turn back to liquid. Anytime a system is converted it may not cool as well because it was not designed to use 134A. The low side seems high, which could be from the difference in refrigerant being used. Sometimes there are retrofit expansion valves available for certain models that will meter the refrigerant better. We don’t sell parts though so check with a retor AC company. I would also make sure that the recirculate door is working properly. Good Luck.

  311. Leon :

    Date: August 22, 2014 @ 12:28 pm

    Hi Dennis,
    When recharging my Honda Pilot with refrigerant, the low side pressure goes passed the 60psi compressor on. when the engine is off and the system low on refrigerant, it’s at 30psi. And I’m using a 12oz can which feels half full…
    The last time I filled up the system, I stopped when the pressure hit 60psi fearing to over-charge and the A/C worked fine for at least 2 months. But the problem is I’m not able to fully charge because of this. Any ideas what the problem could be? Thanks

  312. dennisb - Auto Tool Sales :

    Date: August 22, 2014 @ 1:30 pm

    Hello Leon. I’m not sure why you think the system is low (besides it not cooling well). Low refrigerant isn’t always the cause of a system not cooling well. In this article you should see that 30 psi. on the low side is about normal, high side should be around 275 psi. Not knowing what the high side is, on your vehicle; I can only go by the 60 psi on your low side, which indicates the system is overcharged or the compressor is not pumping sufficiently or the condenser fan is not pulling enough airflow. I would check both readings and check the system more thoroughly before just adding refrigerant. Good Luck.

  313. Melo :

    Date: August 26, 2014 @ 11:05 pm

    Hi Dennis, I’ve got a 1996 Honda Accord and the AC wasn’t cold at all. I did a vacuuming down and a recharge with 1.50 lbs. It was cold for a short time and then started back blowing just cool. The ac line is real cold. The high side gauge reading is 210 and the low side is 40. I replaced the expansion valve twice, the dryer once and still have the same results. I took both lines from the condenser and blew air through and there was no debris or oil came out just air. I need your opinion please.

  314. janae :

    Date: August 27, 2014 @ 3:35 am

    My husband was changing out our battery on our 2011 dodge caravan when my father in law hooked it up wrong there was a spark and now our ac won’t work it only blows hot air. We have changed the switch cleaned out the filter as well as changed the fuses. It still won’t blow cold air we have also tried additional Freon but the pressure shows it at 100 psi and won’t change. We have looked at our ac compressor and it isn’t turning on but it hasn’t locked up. Do you have any idea what else we can do?

  315. dennisb - Auto Tool Sales :

    Date: August 27, 2014 @ 10:22 am

    Melo, I would check the heater control valve in case it’s not closing all the water off all the way. Sometimes the cable needs to be adjusted or else it’s like your heater is on partially and the AC cannot overcome it. See the image below.

    Honda Heater Valve

  316. dennisb - Auto Tool Sales :

    Date: August 27, 2014 @ 10:27 am

    I would double check the fuses there could be several fuse panels sometimes one under the hood and one inside the passenger compartment. Other than that it will take some knowledge of wiring and testing along with wiring schematics and test equipment to trace the fault. Electrical diagnosis is not a DIY task. Godd Luck.

  317. Melo :

    Date: August 27, 2014 @ 8:53 pm

    Hi Melo again I did check the cable on the heater valve working properly open & close all the way unless if the valve is bad internal is it possible ?

  318. dennisb - Auto Tool Sales :

    Date: August 28, 2014 @ 7:34 am

    Melo, it’s not likely that the inside is faulty. If the hose is cold on the other side of the valve I’d say that’s not your issue. You may benefit from having a local repair shop take a look at the system. Good Luck.

  319. Robert :

    Date: September 1, 2014 @ 11:49 pm

    Hi Dennisb. I have a 2004 Dodge Ram 1500 5.7L. Replaced compressor (leaked refrig around housing). Also replaced accumulator and orfice tube. Pulled vacuum for an hour. Inpected for leaks after 30 mins (still 28 in mercury). Charged system partially with engine off-about 3oz, as vapor cyl valve up. Then reharged with engine running. Now orfice/liquid line to evap freezing up. Static press Low 102psi high 100 psi, ambient temp at 89 degrees F. Engine running low 15 psi evap temp on gauge 15 degrees F, high side 150 psi 110 degrees on gauge. 90 degrees F ambient 57 degrees at the center vent. Air blowing at vent is limited due to Blend door partially open. Just found out that the door breaks and blocks air flow. system spec’s are 26ozs. I weighed about 1 pound. oil in compressor 3oz + 1/4oz of dye, 2oz at accumulator. I know system is not completely full. My main concern is the freezing up at the orfice line going to the evap. Finally when I shut eng off I hear a hissing noise by the orfice tube area. Pressure on both gauges show 50 psi. Do you think a shortage of oil could cause this condition. Or a fauty evap pressure sensor? Please respond.

  320. dennisb - Auto Tool Sales :

    Date: September 1, 2014 @ 11:59 pm

    It’s normal for the orifice tube area to get very cold. Low pressure equals lower temp. I would fully charge the system. With more pressure (a normal charge) it should function properly. The hissing you hear is the pressures equalizing – which is normal. If there’s any doors broken, I would replace them. Be sure to check them first and don’t just assume. Good Luck.

  321. Caleb :

    Date: September 2, 2014 @ 12:25 am

    I have a 1972 chevy suburban 4×4 factory ac with rear roof ac. Converted to 134a, all new O-rings, drier, both expansion valves, POA update kit, has compressor out of 90’s chevy truck. All vent doors and valves working correctly, evap and condensor are both clean. Evap fan working correctly, and Derale dual electric fans cooling condensor. Static pressure is at 110 psi, 95 degree outside air temp., 1000 rpm low side 36psi high side 225psi 75 degrees out of front vent 82 degrees out of rear vent. 2000 rpm low side 38psi high side 285psi 68 degrees out of front vent 80 degrees out of rear vent. Pulled cover off of evap and only the bottom third is getting cool about 60 degrees and gets hotter as you move up. I believe I have included all info., any assistance would greatly be appreciated.

  322. dennisb - Auto Tool Sales :

    Date: September 2, 2014 @ 8:39 am

    Caleb, those vehicle’s rear AC never cooled very well to begin with. No, with using 134A I wouldn’t expect as good of performance as R12. Perhaps you can check with a classic AC parts supply company to see if there are 134A expansion valves available that would improve the performance. Good Luck.

  323. Caleb :

    Date: September 2, 2014 @ 8:00 pm

    Its not only the rear ac the front is also having the same issue. when I said front vent I should have said front ac unit, and the main evap is only getting cool about 1/3 of the way up temps are the 75 degrees and the 68 degrees. I could live with the rear being warmer but would like to get the front cooler. Thanks for any info.

  324. dennisb - Auto Tool Sales :

    Date: September 3, 2014 @ 7:33 am

    The fact still remains that you have old R12 valves trying to regulate 134A. So I would still check with a retro AC company to see if there’s an update for correct valving for use with 134A. The low side seems a little high. Higher low side equals higher evaporator temp. Perhaps the correct valving will bring the low side down enough to lower the evaporator temp. Good Luck.

  325. Chimchimman :

    Date: September 15, 2014 @ 6:38 am

    Hi everyone, I am a 38 yr HVAC service technician with an AS in Mechanical Electrical Technology.
    Just a few words on refrigeration theory to help some understand what we want to see and what the equipment must see to operate.
    I have far more experience in HVAC/R however have worked on about 100 cars easily and the theory of refrigeration abides by the same principles as far as the basics go and that’s what we need to know as a baseline.
    1st some terms we need to understand

    A liquid “boils” to a vapor.

    A vapor “condenses” to a liquid.
    These are both a change of state.

    Evaporating we remove heat and
    Condensing we reject the heat.
    This is how the refrigeration cycle works.

    2 other terms are
    Superheat & Subcooling.

    is heat added beyond the “boiling point” and is not sensible heat it is latent and ALWAYS involves a change of state.

    is heat removed below the
    “condensing temp” and is sensible heat.

    a pot of 70F water @ 14.7 atmospheric pressure “sea level”
    will “boil” at 212F.
    From the 70F to 212F is sensible as it can be read by the liquids temperature, however any heat added beyond this point is latent heat and involves a change of state, liquid to vapor or steam in this case, 230F steam is 18 F superheated.

    Consequently de superheat it and condense it to a liquid and at this point any further cooling is sensible and can be read by the liquids temperature.
    200F water is 12 F subcooled.

    A compressor must pump up the refrigerant to a temperature/pressure that will make the outdoor air cooler in comparison so that the condenser coils can reject the heat to the outdoor air.
    Residential condensing units will condense around ambient plus 30F.

    So on a 95F day a 125F condensing temp is expected, as the refrigerant is leaving the condenser via the liquid line, ideally it will be about 15F sub cooled, sub cooling adds efficiency and is a good thing, over 15F subcooling and it may be overcharged.

    The evaporating side will “boil” or flash liquid to a vapor and in doing so it removes a great deal of BTU’s which must be rejected outdoors to the air which may be 125F in Saudi Arabia but if the compressor is pumping the refrigerant to 155F the 125F air is cooler thus allows the heat transfer and condensing to occur so the cycle may repeat .
    The evaporators metering devices are fixed or modulate, capillary tubes are fixes and the high side pressure is what forces the amount of refrigerant through the fixed bore, while a TXV will have a sensing bulb located on the suction line about 1 ft after exiting the evaporator coil, this will modulate to try to maintain a 10F superheat condition, so a 40F coil will have a 50F suction line temp at this point. The compressor is cooled by the col refrigerant so over 200F superheat at the compressor intakes bad.

    A cars compressor is continually varying rpms and the air flow across the condenser coil varies from nothing to freeway air, this will radically affect the condensing temp/pressure.
    A huge fan about 4 feet tall must be placed in front of the vehicle simulating a steady state of air flow so you can see a baseline of high side pressure.
    Avoid even using the high side if the units cooiling at all, the hose alone holds an ounce or 2 and the cap tube systems are far more a critical charge unit to operate well. A TXV type system can easier handle a bit extra refrigerant as the liquid line has a receiver that holds it easily and the metering device does not rely on the high side pressure to operate at its normal state, the superheat is what controls the TXV via the sensing bulb on the suction line.
    If you have a 105 interior temp or a 70F temp will radically affect the output, in residential if you get a 20F Delta T which means temperature differential from the return air and the supply air that is design condition IF its 95F outside and 80F indoors and humidity is 50%

    With 80F indoors temp a 60F supply temp is optimal, this requires a 40F evaporator coil temperature to get the 20F temp split or DELTA T.
    If the suction line(fatter one) is “beer can cold” and wet, its not too far off if at all.

    On the other hand, if the suction lines not cold no bother about the high side as its low clearly for some reason plugged or ??

    To say high side 200 to 350 is really not telling us at what temperature automotive condensers will condense under design conditions which for a car may be different than a house but the theory as to evaporating and condensing still apply to an elementary level which is what we work with when troubleshooting .

    For example a high side of 200 psi = 131 F while 350 psi = 174F.

    To put out 50F air a cars evaporator has to be operating either 15F colder or 40F colder depending on which theory cars follow refrigeration or HVAC.
    I can guess safely its a 15F colder coil as a 40F would put the coil around 10F which will ice up easily.
    So say you want 50F air supplied, the cars existing temps may be 80F or 95F or more plus the humidity is removed before the full DELTA T is ever realized as the removal of moisture is latent heat not sensible involving a change of state, it moves a great deal of BTU’s in doing so but not sensibly until the humidity is reduced first, this is why you see cars with AC running continuously dripping clear condensate water.
    Anyway a 50F supply will need a 40F evaporator coil which equates to a 35 psi pressure and that sems to be what most say is ball park.
    But imagine if you have a cap tube system that the high sides pressure determines the refrigerants volume a 200psi to 350 psi high side will really make a big difference on the refrigerant the evaporator coil gets.
    Regardless of what type metering device used they all require a minimum 100 psi differential between the high side and the low side pressures.
    Hope this helps a bit.

  326. dennisb - Auto Tool Sales :

    Date: September 15, 2014 @ 10:46 am

    Thanks for taking the time to comment. I actually prefer the KISS (Keep it simple) approach when explaining the way a car’s air conditioning system works. I try to use terms that are easily understood by anyone no matter how much or little knowledge they have in A/C theory. Obviously there’s many ways to look at this though.

  327. rick :

    Date: September 30, 2014 @ 10:03 pm

    I have an 88 GMC Sierra 1500 that I converted to R134a in 2000. I replaced hoses, compressor, drier, orifice and o-rings in 2011, and for the last three days I have been trying to add R134a with no success. At 77 y.o.a., I discovered I had the yellow manifold gauge hose connected backward so I pulled vacuum for 30 min (but only in hose..daaa) and to top that stupid act, I left the high side hand valve open and started the engine while trying to charge..daaa. Compressor got extremely hot real quickly, (had jumper on relay), so tomorrow I will replace the existing compressor, drier, and orifice, and start all over with more awareness to pay attention to the little details. Oh yea, my lines vibrated loose on the evaporator since my 2011 upgrade which ultimately caused the leak that created the need for me to be totally frustrated in doing something so simple as adding a can of R134a. Keep up your great advice to others.

  328. dennisb - Auto Tool Sales :

    Date: October 1, 2014 @ 7:16 am

    Rick, conrats for getting out there and working on it. Not too many 77 year olds would attempt it. Active mind and active body – maybe that’s what’s keeping you young! Having the yellow hose backwards (because of the Schrader valve opening only in one direction) can cause the valve to isolate the vacuum. That’s an easy mistake to make, but when pulling vacuum (if working on an empty system) you’d see no change in gauge readings. The same is true for charging or adding refrigerant. The gauge readings should change. I never recommend jumping a relay or low pressure cyling switch to charge a system. It’s simply not needed because when the pressure goes up to a safe level, the compressor will cylce on. This is a safeguard for the system that helps prevent damage from running the compressor without eneough lubricant (the oil circulates throughout the system with the refrigerant).
    If I was working on your GMC, I wouldn’t be so quick to condemn the compressor, just because of the mistakes that were made. The compressor may still be OK, no one knows until it’s checked. If it pumps properly, with good gauge readings and is not noisy, I’d let it ride. Good Luck.

  329. rick :

    Date: October 1, 2014 @ 1:09 pm

    Dennis, thanks for the moral support. I pulled the compressor today anyway and it had 1oz black/rubbery oil in it and the drier had 2oz greenish light oil so I think I as doomed anyway. I blew out open lines with dry air, no debris or restrictions. Will add as much PAG150 to new compressor as I can, Then manually turn shaft before starting charging, then I will estimate rest of 8oz to add to new drier. May even hold back 2oz since some oil may still be in evaporator. Appreciate your info in not jumping clutch relay. Guess that was old school R12 trick. Have a great day!!

  330. Larry :

    Date: October 15, 2014 @ 3:00 pm

    My 2010 Ranger doesn’t seem to cool quite as well as it used to, but it’s not uncomfortable. My manifold gauges read equal static. When running I’m seeing a high of about 220; low about 43. Does the low seem too high? What might cause the low to not be lower? Thanks.

  331. dennisb - Auto Tool Sales :

    Date: October 15, 2014 @ 5:25 pm

    Larry that sounds about at idle, around 800 RPM’s. I’d check the vent temp on MAX at around 1500 RPM’s and the blower speed on low. It should be getting into the 40’s or low 50’s with an outside temp in the 80’s or low 90’s. Good Luck.

  332. johnmc963 :

    Date: December 29, 2014 @ 8:37 pm

    I have a Ford Explorer 2004 with 150K miles. It runs good and have not had many complaints. It’s getting hot outside and it has been blowing hot for awhile. So I went to Auto Zone and I added Freon (with a leak stopper) and it’s still blowing hot. BUT I have a brownish mist that I can not locate. It is all over the place. HELP

  333. dennisb - Auto Tool Sales :

    Date: December 30, 2014 @ 7:52 am

    Leak stop can cause other problems so I do NOT recommend using the stuff. If the brown mist is coming from the air blowing out the vents, you most likely have a leaky evaporator core. I’d use a leak detector to find the leak. I would also try to flush the stop leak gunk out as much as possible. You cant’s flush the compresssor unfortunately. Good Luck.

  334. DL :

    Date: March 16, 2015 @ 10:37 pm

    I have an 08 Mustang and I just tried to use the ac and it doesn’t blow cold just more like luke warm. I figured the refrigerant might be low so I bought an R134-A refilling bottle. It only has a gauge for the low side; when I hook it up to get a reading it jumps up to 40 psi for maybe 2 seconds then drops to 0. It keeps doing this over and over. I did not add any refrigerant its not a definite low or high reading. Any thoughts on what might be the issue?

  335. dennisb - Auto Tool Sales :

    Date: March 17, 2015 @ 7:30 am

    Probably low from a leak. I’d check both sides (high and low) with a gauge set. Pressure without running should be around 80 psi. Good Luck.

  336. zack :

    Date: April 13, 2015 @ 9:27 pm

    I’m about to redo my entire A/C system. The compressor has not been running for months now for whatever reason. I haven’t had cold AC in years, even when the compressor was running. So at this point I don’t think it has any refrigerant or pressure in the lines. I have a manifold gauge set. How do I determine whether there is any pressure or refrigerant in there? If I have a 0 psi reading on both sides (static). Would it be safe to assume everything is gone and its cool to start opening lines?

  337. dennisb - Auto Tool Sales :

    Date: April 14, 2015 @ 1:19 pm

    Yes, however with a zero reading you may still have a little pressure so wear safety glasses. Good Luck.

  338. Gene :

    Date: May 11, 2015 @ 12:37 pm

    Hi I have a 2005 corvette cooling fans run on high at start up and compressor will not engage when turn to high cool. I checked pressure with gauges and both sides are equal with compressor forced to run but blows cold air. Any help would be appreciated.

  339. dennisb - Auto Tool Sales :

    Date: May 11, 2015 @ 12:57 pm

    Gene, sounds like you are getting both readings from the low side. On some GM cars they installed a high side service port on the low side, I think it was for the factory fill, to make it easier to access. Nevertheless, if you are getting a low reading, the line’s cold and your’re getting cold air from the vents you’re probably hooked up to the wrong fitting for the high side reading. You should never need to force the compressor to run. The low pressure cycling switch is a common failure though. Good Luck.

  340. 06expy :

    Date: May 14, 2015 @ 6:03 pm

    Hi,I have a 06 Ford Expedition, front and rear AC.I live in a hot climate and outside temperatures near to 104F to 110F in summer, sometimes ever a bit more. I experienced bad cooling and consulted some technicians and got compressor,condenser, expansion valves, accumulator, high and low-side pressure switches replaced, got both front and rear evaporators cleaned from the inside and all aluminium piping via cleaning chemical after getting them all removed from car. All the replacement parts that I bought and got installed were genuine Ford OEM and new, and were installed in my presence. Blend doors both front and rear are fine. The car only cools when i rev up the engine or when i drive, on idle at 1000 RPM’s there is just mild cold air like fan. There is sufficient gap between radiator and condenser. The car comes with just one engine fan, I added two more in front of condenser with air throw inside same direction as radiator fan, I tried disconnecting the heater lines too. In evening when sun is down the car cools well even on idle but never in the hot day time except when I rev up the engine to 1500 – 2000 RPM’s or when I drive. Compressor cycles normally. When stationary in hot say it stays on since it tries to cool. At 110F outside temp Lo side 40PSI hi side 300 PSI RPM 1000 (idle) vent temp 68F, reving up to 2000 makes it cold lo side 30 PSi Hi side 350 Psi vent temp 57F. In evening vent temp goes 52F even on idle and compressor cycles normally. Kindly advise. I love my car but I’ve spent so much money and time yet this issue is unresolved.

  341. dennisb - Auto Tool Sales :

    Date: May 15, 2015 @ 7:31 am

    It’s been my experience that Expeditions and other SUV’s with rear AC systems, don’t cool as well as vehicles with just a single front AC. I believe that’s because both front and rear AC evaporators are sharing one front condenser. With that being said, all we can expect our AC systems to do is have a vent temperature of around 35 to 45 degrees cooler than the ambient (outside) air. When it’s 110 degrees outside and your vent temp is 57 that’s actually good. That’s 42 degrees cooler than the outside air. I believe your AC is doing as well as it ever will. Especially since you’ve added extra condenser fans. Solar window tint (not just regular window film) may help some. It reduces the heat transferred through the windows from the Sun. Dark vehicle colors also experience more radiant heat transfer. If you have anything besides a white exterior color, in the “desert like” temps that you’re describing, I would consider installing a radiant barrier between the headliner and roof.
    Radiant Heat Barrier
    Maybe in the doors as well. The roof gets most of the direct sun though so this may help the most. Bottom line is they may be a few things you haven’t done, but as far as the AC it’s doing the best it can. One final suggestion is to only run the front AC, if there are no passengers in the back. The AC vent temperature should be a little lower because you won’t be splitting the condenser’s cooling ability between two systems (front and back). Good Luck

  342. 06expy :

    Date: May 15, 2015 @ 3:59 pm

    Am very thankful to you for the answer. But what you mentioned regarding the dual ACs I dont much understand. The output line from accumulator divides into two each going to a separate evaporator after the respective expansion valves. Turning off the rear AC only turns off the blower, the freon still passes in through the rear evaporator so it would be distributed.
    I have a land cruiser with same dual ACs and it runs great no matter I use one or both.
    I have been researching about block type expansion valves, and I located a tuning screw beneath it, turning it clockwise facing it would tighten it and push a spring inside that pushes a pin type thing blocking the air flow. I know if i do this it will increase superheat as the refrigerant will enter into the evaporator more vapourised, hence must cool better. I dont know if doing so has made a difference, right now I have tightened it completely. loosening it alot hasnt helped either, neither another setting.
    I believe in three things, and I guess you would agree, There is some kind of setting to be made to the expansion valve, or the freon should be increased or reduced, or some arrangement to make the engine room desipate its heat to make condenser work more effectively.

  343. dennisb - Auto Tool Sales :

    Date: May 15, 2015 @ 5:27 pm

    When not running the rear AC, regardless of if the refrigerant is pumping throughout the rear evaporator and system; it is not exchanging heat and cold, therefore it’s not cutting down on the effectiveness of the sole condenser.

    I’ve never worked on Land Rovers, however, in the many Fords and Chryslers that I’ve seen with dual AC, have never cooled that well. This is from my experience working in the field in Florida for many years performing AC repairs.

    I never tried to change factory settings on an expansion valve so I cannot advise you on that. I leave the design of AC systems to the engineers.

    Like I said before, your vent temperature is 42 degrees cooler than the outside air. So in my opinion, I don’t think any tweaking of and expansion setting will help. I would look at other ways to increase the efficiency. Good Luck.

  344. mikeginob :

    Date: May 17, 2015 @ 2:48 pm

    Need help with a used car I just bought. Car is a 2000 Mitsubishi Eclipse GT with 3.0 V6 with 146 k miles and the issue is warm air at idle coming from the vents. With ambient temp equal to 76F the low and high side measures 76 psi with the AC off. With the AC on and at idle the low side is 60 psi and the high side is 100 psi. With the AC on and the rpm increased to 2000 the low side drops to 35 psi and the high side remains at 100 psi and the temp in the vent starts cooling down to 40F. What is keeping the low pressure from decreasing at idle? Bad compressor, bad compressor clutch, something else?

  345. dennisb - Auto Tool Sales :

    Date: May 17, 2015 @ 4:05 pm

    Could be worn compressor. The high side reading doesn’t seem accurate though at all. 100 PSI on the high side would not be a reading that would indicate that the compressor is pumping. You may have a bad gauge or connection. Good Luck.

  346. Gene :

    Date: May 20, 2015 @ 5:56 pm

    Dennis Thanks for the response earlier on my 2005 corvette. If my car blows very cold air out of vents when I force the compressor to engage could the compressor still be bad or do I have a different problem not letting compressor engage. I have changed high pressure sensor. I can not find a low pressure sensor. Thanks

  347. dennisb - Auto Tool Sales :

    Date: May 20, 2015 @ 7:33 pm

    Most common cause is the low pressure cycling switch which is usually located on the accumulator/drier. If that is not it, some electrical trouble-shooting is next. Good Luck.

  348. tom :

    Date: May 27, 2015 @ 2:31 am

    Thanks for any help, I have a 03 Lincoln town car ac blew around 60 when i would get on freeway thought it might be a little low added a 12 oz can blew colder now at 50. Low pressure was at 25 now at 35 high pressure now at 250 @92° ran car with gauges hooked up the low pressure keeps dropping to 16 which cycles the compressor off until it hits 60 turns back on does this over and over every 10 sec. This with air on full blast/recirculate fan on high not sure why low pressure drops so much so fast high pressure stays about the same until it cycles off and drops as low pressure rises back towards 60 then back to 250’ish maybe clogged orifice?

  349. dennisb - Auto Tool Sales :

    Date: May 27, 2015 @ 7:15 am

    Tom, most likely still a little low. The cycling switch will try to average 30 psi. for the low side. More than likely you have a leak too. Common leaks on the 03 Lincoln Town car are usually, the hoses, the compressor or the evaporator. Check everything though. See our other AC articles on finding leaks. Good Luck.

  350. Joel :

    Date: May 30, 2015 @ 2:35 am

    Can you tell me the purpose off the high pressure cutoff switch if the high pressure relief valve blows before the pressure of the cutoff switch, blows at about 400 the switch is set to 435, dealing with this problem for a couple years. 96 f150. I have replace all ac components, some twice. Compressor, dryer, condensor, evaperator, all hoses, both switches, etc. completely vacuumed system and charged and runs fine until I shut it down for a while then on startup high side just keeps climbing until pressure relief valve blows loosing freon. Spraying a mist thru the grill does seem to drop the pressure but fan clutch feels fine, any thoughts?

  351. Nate :

    Date: June 13, 2015 @ 3:43 pm

    About 2 months ago, my AC stopped working if the gas was not pressed. It would get hot/warm at a red light, then cool as soon as I started moving again. Two weeks ago it started getting warmer even when driving. A week ago it was warm all the time. I thought I had a freon leak. I bought the freon charging can. When I connected to the low side port (car on, AC set at max) the gauge peaked out at 200+ PSI. It is 90 degrees today. I think the AC compressor is running but am not sure where to look. 2005 Saturn Ion. Any DYI suggestions, or am going to a shop?

  352. dennisb - Auto Tool Sales :

    Date: June 14, 2015 @ 7:56 am

    Nate, I would check the gauge readings and go from there. Saturn’s do have a common problem with compressors though. Good Luck.

  353. 98Expedition :

    Date: June 15, 2015 @ 2:53 am

    Hi, I am hoping you can help me figure out what is going on. Last summer, the A/C on my Expedition started getting weak. I had it checked, and there was a leak found on lines going to the Rear A/C. The cost of the repair was too high, so I decided to chance it with A/C Pro. I added a full 20oz can. The A/C worked much better after adding the refrigerant. That was near end of summer season last year. The A/C was adequate until the last couple of weeks when the temps here in Phoenix went above 100F. I thought that the leak was not fixed, and that I needed more R134a. I hooked up manifold to High side and another can of A/C Pro to Low side. Pressures at idle with approx. 105F ambient was about 60psi on low side and 260-270psi on high side. The static pressure was about 110psi. I also noticed that the compressor engaged when I turned on the A/C, and then never disengaged. Isn’t it strange for compressor to just stay on? The temp of output air was about 68-70F on both front and rear vents. Based on what I have read here, now I am wondering if I actually over-charged the system last year, and causing poor efficiency. Any advice would be greatly appreciated. Thanks

  354. dennisb - Auto Tool Sales :

    Date: June 15, 2015 @ 7:51 am

    Could be overcharged, could also have issues from the stop leak in the “AC Pro” you’ve added. Stop leak can wreak havoc on AC systems and recovery/recycle equipment. Not sure why products with stop leak are allowed to be sold. Many shops without added filtering for their AC recovery machine will turn customers away if they know there’s stop leak gunk in the vehicle’s AC system. I would take to a repair shop and have the Freon recovered and the system pulled down into a vacuum and the proper charge (with the correct refrigerant) put in. And then recheck. It may also be possible to cap off the rear AC, if that’s where your only leak is and you can’t afford to fix it. Good Luck.

  355. Jeff :

    Date: June 22, 2015 @ 2:42 pm

    My AC vent temp is 70 degrees at 1500rpm, ambient air is 90 degrees.
    Static pressure is 100 w/ everything off.
    Low side pressure 53, high side 250.
    System is blowing cool but not cold air. Compressor is new, condenser is new. I flushed all lines and evaporator w/ Dura II. Vacuumed for 1 hr to 30mmHg. Held vac for 15 mins afterwards. Then charged with 4 oz pag oil and 1.76 lbs 134a as dealership told me.
    My low side seems hi? but everything else looks fine….why are my vent temps so lo poor?
    2003 Silverado 2500HD.
    THANK YOU!!!

  356. dennisb - Auto Tool Sales :

    Date: June 22, 2015 @ 2:50 pm

    Jeff you can’t flush the expansion valve (or compressor) so, unless it was not hooked up when you flushed, I’d bet that there’s solvent in the system. Even with the expansion valve and compressor NOT hooked up in the system, it’s really hard to get all of the solvent out. That’s why I always preferred using an extra add on filter on systems that are really dirty instead of trying to flush.

  357. Jeff :

    Date: June 22, 2015 @ 2:53 pm

    my pressures are at idle.
    Also, my compressor seems slightly noisy…….being new I thought it would be silent like the OEM was…….new one is a Delphi.
    New condenser got 1oz PAG 125
    3 ozs went into new accumulator.
    I was told 2 ozs for evap, 1 oz for condenser and 1 oz for lines……totaling the 4oz I put in.
    It seems like I need more 134a but the pressure already seems hi to me and I know I have the correct charge amount in the system anyway.(1.76lbs)
    also, evap inlet cold, evap outlet not so cold…cool at best.

  358. Jeff :

    Date: June 22, 2015 @ 2:54 pm

    I did not flush compressor……just added the amount of oil that was in the old one………..I removed all lines to flush them.
    So you believe my evap is full of flush solvent???

  359. dennisb - Auto Tool Sales :

    Date: June 22, 2015 @ 3:40 pm

    It’s possible. The evaporator and condenser are very hard to flush to remove ALL solvent. Lots of tiny tubes, especially the condenser. Anything other than refrigerant in the system, like solvent, excessive oil, air etc, can cut down on the efficiency making it not cool as well.

  360. Akram :

    Date: June 28, 2015 @ 11:55 pm

    Hi, I have a 2010 Ford Expedition not cooling well at idle speed. The compressor and expansion valve are new. The low side pressure is 30 to 40 psi. It is a single ac and is coldest when around 2000 RPM’s.

  361. dennisb - Auto Tool Sales :

    Date: June 29, 2015 @ 7:04 am

    I would check both high and low gauge readings. Also check vent temperature with a thermometer with AC on MAX so the cabin air recirculates. The readings will help determine what’s going on with the system. Good Luck.

  362. spanky :

    Date: July 1, 2015 @ 11:28 am

    Hey I have a Snapon electronic leak detector from the 80’s. Will it work on 134a it was made when we still used R12?

  363. dennisb - Auto Tool Sales :

    Date: July 1, 2015 @ 12:24 pm

    More than likely. You could always test it at a service port to verify.

  364. BurgieDanny :

    Date: July 3, 2015 @ 7:20 pm

    I have A 1999 Dodge Stratus, the A/C only seems to work well when it’s cool outside. Today it was 92 degrees and the air would only go down to 68 degrees. This is what I did to the A/C today. I changed the Accumulator/Drier and the Expansion Valve. I flushed the Lines, Evaporator and Condenser. I removed the Compressor emptied the oil and refilled with 5 ounces pag 46 oil. I pulled vacuum for 1 hour and filled with 19 ounces of Freon after venting lines to evacuate air in the lines. The Gauges are showing 46 on the low side and 200 on the high side, its 92 degrees today so I believe the readings are low, but Ive already filled to manufactures specs. The condenser fan seems to be running on high like it should and Ive cleaned the Condenser with engine degrease and the garden hose. What am I missing?

  365. dennisb - Auto Tool Sales :

    Date: July 4, 2015 @ 9:37 am

    Normally, there’s no reason to flush a system unless the compressor has failed and you are installing a new one. If the oil is black that indicates a worn compressor and it should be replaced. You don’t normally change oil in an AC system like you do in a car’s engine.
    Hopefully you didn’t vent the Freon into the atmosphere. This does harm to the ozone. A shop with an AC recovery machine should be used to recover refrigerant before starting to work on a system. Never heard of using degreaser on condenser. Usually there’s just pollen and dirt, not grease or oil. If there was an oily residue, that indicates a leak. The low side on Chrysler vehicles is usually 15-20 PSI. So, 46 is high. Causes of the low side being too high on your model is typically a bad expansion valve. I know you replaced it, but it could be defective. Could also be the compressor not pumping sufficiently. I would expect the low side lower and the high side higher. So, I would replace the compressor and expansion valve. You could try the compressor without replacing the expansion valve first if you wanted, but I would get it warrantied just in case. You’ve already replaced the drier. Good Luck.

  366. BurgieDanny :

    Date: July 4, 2015 @ 10:57 am

    I didn’t vent the freon, I have an rg5000 recovery machine. I’ve been trying to get this ac working right for a few weeks now so I went ahead and tried every thing except replacing the compressor! When I vacuumed the system I could only get it down to -22 and I’ve read it should get down to -29. could I still have moisture in the system? I used the rg5000 to vacuum, maybe its not strong enough? it sat at -22 for 30 min, I don’t think its leaking. I’m new to this a/c work and my wife’s gonna buy a new car if I can’t get the a/c working right! I really appreciate this!

  367. dennisb - Auto Tool Sales :

    Date: July 4, 2015 @ 11:42 am

    There’s either a leak in the car’s AC, the gauge/hose assembly or the gauge is just wrong. Moisture will not cause an incorrect vacuum reading.

  368. BurgieDanny :

    Date: July 4, 2015 @ 12:36 pm

    I didn’t think the vacuum reading was incorrect, I thought because I didn’t get it to -29 I left moisture in the system and that’s why I was getting the pressure readings and a/c was not cold enough. according to charts, low side should be 45-55 and high side 275-300. but my high side reading was low and I didn’t wanna just keep adding freon when I was already at 19 ounces. I guess next is a new compressor, thanks for the help.

  369. Jeep zj :

    Date: July 5, 2015 @ 5:42 pm

    I have a 1994 Jeep Grand Cherokee Laredo 6 cylinder . I just replaced all the ac components and evacuated the system . I put in less than 1 pound aim getting 48 psi on low side and 90 on high and blowing hot air

  370. Steve :

    Date: July 6, 2015 @ 10:26 am

    I have a 1994 Ford F150 XLT, 5.0 liter. when it was purchased a couple years ago, the air conditioning was weak. The sellers filled it with Freon, it was blowing warm within a couple days.

    Two years later we are starting to work on it. lowside pressure was 8 pounds, high side 0. The compressor would not kick on until I jumped it, then it came on. It started taking the first can of freon (134). Lowside dropped to a vacuum of about 15 and I periodically checked the high side. It was building up gradually, then seemed to stop at 125 psi. I thought the first can was empty. It really was not. I hooked up the second can, and the system would take no more. The low side had gradually crept up to zero, and now was staying there. The high side would not go past 125 psi, and after a few minutes actually dropped to 120.

    I am not good at air conditioning systems, but I am very mechanically inclined. This is the first time I have added freon in my life, and my first set of guages. Any help you can give would be appreciated. Do you think the compressor is tired?



  371. dennisb - Auto Tool Sales :

    Date: July 6, 2015 @ 10:28 am

    Wow, not sure why you would replace ALL components. At a full charge you should have around 30 on the low side and around 300 on the high side at around 1500 RPM’s. At a partial charge, the fan may not be on which would cause a higher than normal low side. Lower RPM’s would cause a higher than normal low side also. Refrigerant not drawn into the system will cause a higher than normal low side, although it shouldn’t take much pumping to bring the low side reading down. Good Luck.

  372. dennisb - Auto Tool Sales :

    Date: July 6, 2015 @ 10:37 am

    Jumping the clutch to engage the compressor bypasses the safety which protects the compressor. It’s not needed to charge a system, so I don’t recommend it. It’s not good for a system to be left empty. This allows seals and orings to dry out which can cause leaks. I would stop and check for leaks since you have enough in the system to check. After leaks are repaired I’d vacuum the system down and charge and recheck. To answer your question about the compressor being worn, yes that’s a possibility. Without a full charge it’s hard to tell though. With the low side in a vacuum the Freon should flow into the system if the valve is opened properly if the compressor is good or not. Good Luck.

  373. Justin :

    Date: July 29, 2015 @ 11:04 am

    Hey, We hooked up my 2005 BMW 525i A/C up and we got a low reading on both sides. We decided to vacuum the system. We got it to -10 and it basically didn’t drop over our wait. We recharged the system to 50 (90degrees outside) on the low side and the A/C was blowing good about 65 degrees. Better than 90 or 95. We turned the car off waited a while and then started it again to test pressures. The low pressure was high about 70 and the high pressure was low about 200 and the needle was jumping up and down about 5 both directions. The A/C was blowing about 80. Any idea of what could be happening?

  374. dennisb - Auto Tool Sales :

    Date: July 29, 2015 @ 11:10 am

    Justin a vacuuming down of the system should only be done on an empty system. It should go down to 28-29 not 10. A leak could be the issue with the system or the gauge set. Since the low side is high and the high side is low, this indicates a weak AC compressor. Good Luck.

  375. Tim :

    Date: July 30, 2015 @ 8:35 am

    I have a 1995 Chevy silverado. When the A/C is off and the recycle is off, the controls for the air direction work fine. I turn it to vent and it blows out the vents, floor and vent and etc. etc. I turn the A/C on and the air flow goes directly to the floor, and the control to change the air direction will not work. It did this for about 3 months, and the air was cold. Now the A/C is not cooling at all. The controls are still doing the same thing. Any ideas will be helpful.

  376. jed :

    Date: July 30, 2015 @ 9:44 am

    I have a simple question, but have looked for the answer for days. 2004 Honda Accord EXL 4 cyl, A/C only cooling to 65 deg in right center vent and passenger vent, drivers side vents basically not cooling. I have has the Compressor and serviced (last year). Things I have noticed that may be a problem 1. High pressure line and low pressure line near the servicing ports are close to the same temp, 2. Bottom 1/3 of the condenser is almost closed off due to fins bent due to road degree.

  377. dennisb - Auto Tool Sales :

    Date: July 30, 2015 @ 10:45 am

    Jed, not sure what the question is, but I would check the readings to see what’s going on with the system. The blockage could definitely affect the efficiency of the system. The high reading would be high if too much air is blocked off from condenser. Good Luck.

  378. dennisb - Auto Tool Sales :

    Date: July 30, 2015 @ 10:47 am

    Most likely a control head issue. Will take some testing with use and knowledge of wiring diagram and how the system works. Good Luck.

  379. Hope :

    Date: August 7, 2015 @ 3:00 pm

    I have a 2002 Dodge Grand Carvan Sport just put new air compressor on it . It has dual air in front and back much freon would I put in it?

  380. dennisb - Auto Tool Sales :

    Date: August 7, 2015 @ 4:46 pm

    Hope, sorry that information may be found under the hood or in a manual. Good Luck.

  381. Jay :

    Date: August 29, 2015 @ 5:01 pm

    My daughter’s 2000 Beetle has been sitting for a couple of years without running while she was off at school. I got it started but the a/c wasn’t working so I hooked up the gauges and got a reading of 90 psi on the low side and 97 psi on the high side. Would this condition occur if it had a low charge?

  382. dennisb - Auto Tool Sales :

    Date: August 29, 2015 @ 6:43 pm

    Based on the static pressures, seems like it has a charge, just maybe the compressor clutch isn’t engaging the compressor. If the compressor is engaging it may not be pumping. Good Luck.

  383. Jay :

    Date: August 29, 2015 @ 6:46 pm

    I checked and the compressor clutch is engaging. If it’s not pumping could this be the RCV?

  384. dennisb - Auto Tool Sales :

    Date: August 29, 2015 @ 7:59 pm

    The RCV (Refigerant Control Valve) is used in some VW’s that have a varable speed compressor. However the high side reading should be higher even if there was a problem with that valve. You could try raising the RPM’s to see if the readings change (to seee if the compressor is pumping any), but more than likely the compressor has failed. Not using the AC for an extended period of time is not good for an air conditioning system, Orings and seals need the lubricating refrigerant oil to circulate throughout the system to keep them pliable so they can seal properly.

  385. Bruno :

    Date: October 28, 2015 @ 9:51 pm

    I have an Excursion with front and rear A/C. If rear A/C is off the front will blow warm. As soon as the rear A/C is turned on, the front will start to blow cold air. Turn the rear A/C off and the front will go back to warm air. Any ideas? Overcharged system?

  386. dennisb - Auto Tool Sales :

    Date: October 29, 2015 @ 7:02 am

    Bruno, I would check the gauges and see the change when the rear AC is turned on or turned off. You could be right maybe overcgharged. The readings should help diagnose. Good Luck.

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