By June 17, 2008 Read More →

Air Conditioner Leaks Freon But Where?

Could help me with a Ford sedan with an air conditioning problem.

I have been all over it with an electronic leak detector for 134A and cannot find the leak although after recharging it with freon it seems to be gone within 3-4 weeks. It makes me think the leak is on the high side because after most of the freon is gone and for months after if I connect gauges to the system, it actually shows a small amount of pressure, which makes me think that the leak is not large enough to take the system to zero without

So obviously we have a leak somewhere, maybe on the high side of the system and my question is do these vehicles have any suspect areas or inherent problem points that always seem to fail so I can check them? The only other alternative is to break open the system and vacuum or pressure check each individual component and fitting.

Also, I have seen vehicles where the compressor shaft seal fails and gas will leak from the seal although they never leaked that quickly and the leak detector will usually pick it up if you can get the tip close enough to the compressor.

Thanks for your help!


Hey there Gary,

Finding a small Freon leak can be tough, even my best mechanics will have times when it takes 2-3 customer returns and 8-9 cans of refrigerant to finally locate the leak. This vehicle is VERY notorious for leaking evaporators and high side compressor hoses.

In fact, we had so many people come to my shop between 93-97? that we made a special hard copy quote page for evaporator replacement that we could hand to people when they came in our shop.

The evaporator is the hardest to leak test because it is inside the dash and hard to reach with the test probe. They make a fluorescent dye that you can inject into the system and use a black light to find the trace of the dye….thus find the leak.

You can sometimes rent these leak detector systems from a local auto parts store. This might be a good place to start. Add the dye and top off with refrigerant and a shot of compressor oil to keep the compressor lubricated, then drive the vehicle until it leaks out.

Then use the black light to look for the leaking dye. You can look inside the evaporator drain hole to see if any dye is present inside the evaporator case. If you don’t see any dye under the hood, I would highly suspect an evaporator core leak.

Yes, the compressor shaft seal can leak, but the dye will make that leak pretty obvious. You will usually see a “sling trail” of compressor oil on the compressor clutch if the shaft was leaking…because not only is the system leaking refrigerant it is also leaking compressor oil. Dust and road dirt will usually stick to this compressor oil at the leak area over time.

Keep me posted as to what you find out will ya?


Austin Davis

Reader Follow up

Thanks for the tips Austin! One other person speculated on the evaporator and I was hoping that was not the case. Let me ask you if this makes sense.

I topped off the freon, then closed up the car and ran the air conditioning for a while and put my electronic leak detector right in the air duct flowing from the evap. Since it suposedly can detect 1/4oz per year. I thought if I had that big of a leak I would have gotten something in the cabin after running the unit for 15-20 minutes but did not.

Are the evap leaks you have seen at a sweated fitting or does the core fail? Thanks again for your help and I will let you know what we find!


Hey Gary,

Shoot just a quick shot of Freon from the can inside the cab of the vehicle and close the doors and let the A/C run for a few minutes, then retest. Most “cheap” (under $300) leak detectors that I have worked with only really pick up leaks if the probe is basically sitting on top of the leak itself.

I would say its 50-50 core leak and fitting leaks. Those long high side compressor hoses under the hood take a real beating and undergo a lot of pressure. Make sure you have thoroughly checked it and all condenser fittings.


Austin Davis

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Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

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