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Finding Refrigerant Leaks – Car AC Tips from DenLors Tools

9:14 am Air Conditioning


Refrigerant leaks aren’t always this obvious. The compressor housing was cracked wide open.

© Summary: Master automotive technician provides tips and suggestions for finding refrigerant leaks. There are several methods to help diagnose and pinpoint 134A refrigerant leaks in cars. We cover the most common ways to check for leaks. Also we’ll list where certain car manufacturers weak points are when it comes to Freon leaks. Read on to learn how the pros do it. 

It’s no secret that leaky systems cause low freon and a low charge which can obviously cause the car’s A/C NOT to cool well. If the system is low, we know there’s a leak. The next question is – “How fast is the leak?” If the system takes a year to leak down and only needs 8 oz. – that’s a 1/2 a pound or less, the leak may not be bad enough to warrant repair. If the system is leaking faster, the leak should be identified and repaired. An A/C gauge set will be needed to check the AC system. See our A/C Gauge Readings Explained article for help in understanding what the pressure readings mean. After hooking up the gauges and determining the problem is a low system, you’re ready to start looking for a leak. The next step is to do a visual inspection to look for refrigerant oil residue. Some cars have UV dye in the system already, this helps to find the oil easier. Where there’s refrigerant oil, there’s a refrigerant leak. Even if the car’s A/C system does NOT have UV Dye installed, there should still be oil that can leak out to help lead you to the problem. The oil without dye is harder to see, however dirt tends to stick to the oil making it a little easier to find. Use the following to help find leaks by doing a visual inspection.

1. UV Dye – Put dye in the system if it does NOT already have it installed. Removing the caps and looking at the service ports for evidence or traces of dye is the easiest way to see if a system already has dye in it.

2. UV Light – UV dye can be seen with the naked eye, however a UV light helps tremendously by making the leak GLOW. A trail can be followed in some cases and lead back to the source of the leak.

Finding Refrigerant Leaks with a Leak Detector
It’s important to start with a system that has enough Freon in the system to find the LEAK.  If the car’s AC system has a static reading (Pressure with car turned off) less than 50 PSI, some Freon should be added before using a refrigerant leak detector/sniffer (FYI a sniffer is what many auto techs call an electronic leak detector). Keep in mind that refrigerant is heavier than air and usually goes downward. That’s why it’s best to place the leak detector wand, with the sensor tip underneath the suspected “leak” area. Water drips normally from the evaporator drain tube. Caution should be taken, when checking evaporators near the drain because if water enters the sensor it can be damaged. Otherwise the drain is a great place to check for an evaporator leak since 134A is heavier than air and will naturally go down and out of the drain.
Common Leaks and Failures on Various Models
GM, Chevrolet, Oldsmobile, Pontiac, GMC, etc – GM’s usually have one weak point… the A/C compressor. The evaporator hardly ever leaks on these cars. Ninety percent of the time if there’s a leak on a GM product it will be the compressor. The seam where the compressor is put together is usually where the leak is. Sometimes the top of the compressor is dry, but the bottom of the compressor is oil soaked.
Chrysler, Dodge, Plymouth, etc. – Chrysler products have a reputation of weak evaporator cores. Most of the time if there’s a leak, there’s a very good chance that the evaporator will be the cause. When I worked as a tech, I loved to have a Chrysler AC to diagnose. It usually meant a 4-13 hour evaporator job that I could finish in a fraction of the book time. Out of all the Chrys products, like Dodge Ram,  Durango, Dakota, Sebring, Avenger, Intrepid, 300 … the Town & Country and Dodge Caravan pays the most for doing an evaporator. Flat rate (book time) is around 13 hours. This translated into $50-60 an hour for me.

Ford, Mercury, Lincoln – Ford Motor Company products also have somewhat of an evaporator issue. However, it seems that they don’t give as many problems as they did in the past. In the late 90’s and early 2000’s leaking evaporators were much more common than they are lately. Around the year 2000, Expedition and Taurus’ evaporator jobs provided me with a lot of profitable AC work!

Saturn, SC2, SL – These cars don’t leak much. The AC compressor is still the #1 problem with them

though. They would either NOT pump properly or lock up (seize). I can say I NEVER had to replace an evaporator in one of these cars though.

BMW – These car’s are quite common for having evaporator leaks. Some guys love to work on these cars. I NEVER liked working on them myself. It’s all in what you get used to… just never my cup of tea.
Honda Accord, Civic – These car’s hold up very well. Occasionally an evaporator core can leak or a compressor may fail but I would NOT say they have any common issue.
Toyota Camry, Corolla – Same as Honda when it comes to their AC systems for the most part. Occasionally a compressor clutch coil may fail and cause the AC not to work and the AC switch light to flash. Usually just a failed coil though.
VW Passat, Golf, Jetta, Beetle – Compressors on these cars sometimes explode (or crack like the image at the top of the article). Not a very common issue, but when they fail they sometimes go in a BIG way. I’ve replaced many that had chunks missing out of the AC compressor housing. Other problems, especially with the Beetle are related to electrical controls or modules. For more information on AC servicing and related tools, see the links below.

The tips in this article are very basic and NOT intended to be a complete guide for servicing your AC system. Please refer to a repair manual for further instructions.

Related Car Repair Articles and Products

Basic Car AC Gauge Set Hook-Up

Adding Freon to Car AC – Gauge Readings Explained

Car AC Not Blowing Cold Air – Charging Tips and FAQ’s

Other AC Articles

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2 Responses
  1. steven :

    Date: May 19, 2015 @ 9:50 am

    2001 ford expedition with rear air. came in with frozen compressor bearing. I replaced comp. with used working comp. Removed all lines and flushed, installed new accumulator, and new o-rings at all conections, added comp. oil, now I can’t get the system to hold a vacuum. owner stated that AC has not worked for over a year was leaking 134.the line on the old accumulator was seized upand came out very hard before installing new accumulator cleaned and oiled and the new fitting went back together seemingly with no problem. how do I find where the system is leaking without adding 134?

  2. dennisb - Auto Tool Sales :

    Date: May 19, 2015 @ 11:28 am

    Steve, the easiest quickest way is to add refrigerant. Theres needs to be at least 50 psi to be able to check for leaks with an electronic leak tester. Without adding refrigerant, you can do a visual inspection. Ford puts UV dye in at the factory so you may see evidence of a leak by just looking with the naked eye or maybe easier with a UV black light. Another way to check for a very large leak is to pressurize with compressed air. Pep Boys where I used to be a senior tech at many years ago, had us use an adapter fitting to hook and air hose up to the AC gauge set to put compressed air in the system. You can then use liquid dish wash detergent to check components, looking for bubbles. This only works in my experience if the leak is large and accessible. For instance, how can you check an evaporator inside the dash with soap bubbles? What about a slow leak at the front compressor shaft seal with bubbles? The most common leaks on the Ford Expeditions that I’ve worked on are the evaporator and the compressor. A used compressor is likely to have a dried out front shaft seal which may leak. Sometimes an oil charge circulating may slow the front shaft seal leak down. An acceptible leak there would leak about a 8-10 oz a year. Anything more than that I would definitely condemn it. Good Luck.

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