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Thread: AC leaks out in a matter of days, but no visible leaks

  1. #1
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    926

    My VIN:    767 (3.0L EFI/EDIS)

    AC leaks out in a matter of days, but no visible leaks

    About two years ago I replaced my entire A/C system, front to back, and upgraded to R134a as part of my 3.0L conversion. It seemed to work fine for the first year. At the beginning of this summer it wasn't blowing cold, so I refilled the system. I have a gauge set and a decent enough idea of what I'm doing, thanks to help from others here.

    It worked fine for a month or so, it wasn't as cold anymore, so I topped it off, and it blew cold again. It seems that the leak has gotten worse as the summer progressed, and now it only holds a charge for 2-3 days, loosing around 100 PSI as measured from the high side over that time. I'll fill it one day, and by the next day it's already blowing a few degrees warmer (as measured with an A/C thermometer stuck in the center vent, Max A/C and highest fan speed).

    Over the past few weeks I've added three cans of R134a with dye, but a UV light shows no leaks of any kinda anywhere. Yesterday I added another can, drove for about 45 minutes, then looked all over the system again. I checked at all the joints (compressor, condenser, dryer/accumulator) and all over the compressor itself, and down the hoses (what I could see of them, anyway) but I can't find any leaks.

    Anyone have any ideas for what I should try next? R134a isn't expensive, but it takes 20 minutes to fill the system each time, and I don't like leaking it into the atmosphere.

    Thanks!

    -- Joe

  2. #2
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    If you really aren't get any dye showing at any of the places you mentioned, the only thing left is the evaporator.

    You can try looking into the evaporator box through where the blower motor or blower resistors mount, maybe with a small mirror, and see if you can see any dye.

    Are you sure you have the correct UV light and filtered glasses?

  3. #3
    Administrator Ron's Avatar
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    Another possible hiding place is at the front shaft seal, behind the clutch assembly.
    A sniffer might save you a lot of work...

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    Most common leaks are the service valves but never hear of those causing that fast of leak. To test just put your finger over them after charging. You will feel and hear pressure if they are leaking.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

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    My VIN:    767 (3.0L EFI/EDIS)

    I have a UV light and glasses. They were from an older dye kit I had lying around, and not specifically meant for this specific pre-mixed R134a and dye. I admit that I just assumed they all fluoresced in the same UV wavelengths... Some neon-colored zip ties I used under the car glow under UV, too.

    I do see some fluorescing from the low pressure connector, which is what I'd expect, since that's where I filled it from. It's just a small amount from when I moved the connector, and it's on the connector itself where the gauge set attached, and doesn't look like a leak itself. So I think the light is working.

    I pulled the blower motor and took a look at the evaporator with my phone's camera, but since I couldn't fit my long UV light in there, I didn't provide any useful information.

    -- Joe

  6. #6
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

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    Quote Originally Posted by Ron View Post
    Another possible hiding place is at the front shaft seal, behind the clutch assembly.
    A sniffer might save you a lot of work...
    Somehow the idea of a sniffer existing didn't even occur to me. I've ordered an inexpensive one from Amazon that has decent reviews. Hopefully it actually works properly and finds the leak. I'll report back in a few days, after I've been able to run the test.

    Thanks!

    -- Joe

  7. #7
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

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    My VIN:    767 (3.0L EFI/EDIS)

    Quote Originally Posted by Bitsyncmaster View Post
    Most common leaks are the service valves but never hear of those causing that fast of leak. To test just put your finger over them after charging. You will feel and hear pressure if they are leaking.
    I did think I had a leak on the high side connector for a bit. I had just installed a 90 degree R12 to R134a fitting; the straight ones don't fit on my 3.0L compressor while still letting me fit the quick-release adaptors from the gauge set. There was dye all over the fitting, which was more likely due to forgetting to close the valve on the quick-release before removing it. Removing the fitting had no effect on the leak.

    I do put caps on the fittings when I'm done filling, but I'm guessing those don't do anything significant to keep refrigerant in, but rather just keep debris out.

    For the record: I filled the system about 24 hours ago, and it's already blowing about 10 degrees warmer. I haven't had a chance to put a gauge set on it yet.

    -- Joe

  8. #8
    Senior Member
    Join Date:  Dec 2018

    Posts:    730

    You can also use glass cleaner for a leak detector. Especially on a leak that fast. I've had as much luck with it as my sniffer. The caps do help seal service ports.

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