Car AC Not Blowing Cold Air – Charging Tips and FAQ’sJune 27, 2010 8:45 am Air Conditioning, DIY, How To Auto Repair
© DenLorsTools.com Summary: One of our most common questions about air conditioning has to do with “how to charge a car’s ac.” In this auto repair blog, we cover the do’s and dont’s of DIY car AC refrigerant charging. We have suggestions on how to fill a car’s air conditioning system if doing it yourself. We caution DIY’s of the dangers and the possibility of over-charging a car’s air conditioner. Questions and answers covering AC gauge sets, charging kits, troubleshooting, refrigerant, leaks and much more. Basic step by step directions are provided.
Low refrigerant is the most common cause of a car’s air conditioner not cooling well. There are many other reasons a car’s A/C may be blowing out warm air though. We strongly recommend the use of an AC manifold gauge set when checking a system. Realistically, we understand that many people are only looking for a quick fix and will purchase a do it yourself-er charging hose or a charging kit to add Freon. The purpose of this article is to help those that are going to use a recharge kit to add refrigerant and take their chances. Keep in mind that if a car has a very slow leak, just adding a can every summer may be feasible; but if there’s a fast leak, adding freon is like throwing money out the window. Be sure to click on our related “how to” car repair articles at the bottom of this page for information on using an AC manifold gauge set and detecting refrigerant leaks.
Step by step directions for simply adding freon to an R134 A system.
1. Locate the low side service port. Do not connect to charge hose at this time. The quick connect fittings are different sizes on the low and high sides, this makes hooking into the high side impossible with a do it-yourself charging kit. The service port cap will be black or sometimes blue. It is in the larger diameter line (suction side) or depending on the system, the accumulator.
2. Read warnings and handling information on the refrigerant can. Safety glasses are recommended to protect your eyes. Avoid skin contact with refrigerant. Make sure the piercing needle is retracted and then connect the screw fitting to the top of the can.
3. Start the engine in the car and turn on air conditioning. Set controls to maximum cooling. Connect the charging kit to the low side service port located in step one. The quick connect spring coupler will need to be pulled back while the fitting is pushed onto the port. After it is in place push the sleeve to go back into the down position. Make sure it is in the locked position and is fully engaged.
4. Turn the valve’s knob to the right which will pierce the can. Turn the knob back to the left which will allow the flow of refrigerant (134A) into the car’s AC system. The can should be held upright and shaken. The reason for not holding the can upside down is that vapor will rise to the top of the can. Liquid will be in the bottom. If liquid is allowed to go in to the car’s A-C system and enters the compressor, as a liquid, the A/C compressor may be damaged. The compressor CANNOT compress liquid. Rotating the can quickly between the 12:00 position and 3:00 position while shaking, will help to vaporize the refrigerant while charging.
5. You may feel the can getting cold while charging - this is normal. Get a feel for the refrigerant in the can so it can be determined if there is any remaining in the can while charging. Once it feels empty, the can will be turned upside down to insure the last bit has been drawn into the car’s AC system.
6. If the car is blowing cold air now, the job is almost complete. Avoid adding too much, I’ve said it before in my other articles “more isn’t always better.” (That’s why it’s better to use an AC manifold gauge set when charging.) Close the valve by turning it to the right. Disconnect the quick connect fitting and replace the cap onto the service port.
Questions and Answers – FAQ’s
Question - How do I know if my car has 134A?
Answer - Cars manufactured from 1996 and up will most likely have 134A. The 134A type quick connect fittings are a good indicator. Older cars that have not been retrofitted (that still have R12) will have smaller fittings which are threaded, NOT quick connect type fittings.
Question – How do I know how much freon to add to top off my system?
Answer - You don’t. The only way to know 100% is to use an AC recovery machine to remove all the refrigerant. Vacuum the system down using a vacuum pump and then use a weight scale to put the factory specified amount back in. Mechanics with experience can use gauge sets to help them make an educated guess on how much to add. Our article linked at the bottom covers more when it comes to gauge readings and what they mean.
Question - How do I jump my low pressure switch to make my compressor come on so I can charge the system?
Answer - There’s no need to jump the low pressure switch. The compressor will come on when enough pressure is in the system for it to run without it being damaged.
Question - I’ve just replaced my compressor. How do I vacuum the system down first before I charge the system?
Answer - If evacuating and recharging the system, you need an AC manifold gauge set and a vacuum pump, below are basic steps.
- Measure oil removed when the system has been emptied. The only legal way to empty a system is with an AC recovery unit.
- Replace the refrigerant oil that was previously measured. Note that some replacement compressors come with oil in them others do not. Lack of oil may ultimately cause compressor failure, just like running a car motor without engine oil will cause seizing. (old oil is not to be reused). Turn the replacement compressor’s shaft 10-15 times by hand to displace refrigerant oil (this will help prevent damage to the compressor).
- Vacuum the system down with an AC vacuum pump. The AC manifold gauges should both be OPEN while doing this. The longer the better, but 15-20 minutes ok.
- 28-29 inches of vacuum should remain, if there’s no major leaks. Close both valves, remove vacuum pump. Connect to refrigerant source. Start engine and turn AC on. Start charging the system by opening the BLUE valve which is the low side. Warning: opening the red valve (attempting to charge through the high side) can possibly cause the refrigerant can to rupture!
- Use cans so you know how much refrigerant you are putting in or a scale that weighs the bulk container.
Question - I charged my system but it didn’t stay cold for very long. What could be the problem?
Answer – Most likely there’s a leak that is too fast to make occasionally charging feasible. Use a refrigerant leak detector to determine where the leak is and replace the leaking component. See our article linked below about how to find refrigerant leaks.
Question - Since you sell them, parts stores and even Walmart sells charging kits; why don’t you recommend them?
Answer – Using a simple charging kit with NO gauge is like walking in the dark. You may find your way around, but you may stub your toe! Adding freon to a system without a gauge set makes it much more difficult to end up with a proper amount of charge since there’s blind guesswork involved.
Question - I know I have a coolant leak in my AC system. Should I use the freon kit that has stop leak in it?
Answer - Not a good idea. The stop leak may slow the leak down. It may also damage the compressor, clog up the condenser, evaporator or expansion valve. If you end up taking the car to a repair shop and they find that there’s stop leak in the system – they most likely will refuse to work on it. Stop leak wreaks havoc to expensive recovery units. In fact we sell a filter to help prevent damage to AC recovery machines because it is such a problem. Just to clarify; the refrigerant in the AC system is NOT called “coolant.” Coolant or anti-freeze is in the radiator/car engine’s cooling system NOT the air conditioning system.
Question - I need change a part in my AC, how do I get the freon out?
Answer - Take it to a shop and have them recover the refrigerant. Then take the car home and change the failed part. It’s the only way to remove the refrigerant without having an expensive RRR (Recovery, Recycle & Recharge) machine. A recent customer mistakenly thought that a vacuum pump was designed for recovering/emptying a system – this is NOT the case.
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