Engine Size: 4.2l
Refrigerant Type: R134a
Ambient Temp: 80
Country of Origin: United States
I've been struggling to find the leak in this system for quite some time. UV dye, and bubbles, have not found anything. Finally took the A6 compressor out and did see some evidence of dye around the shaft. Replaced the seal with the newer double lip type. Pulled a vacuum on the system and rechecked it a WEEK later--no change! Thought all was good so replaced the drier, pulled vacuum. Next day, vacuum still the same so charged system. Cold air lasted somewhere between 24 and 48 hours. Pressures down, as expected.
Now, a week or so later, I presume there is still some refrigerant in the system, as pressure is about 35, with system off. So vacuum seems to hold, but not pressure. Would you tend to suspect the new compressor shaft seal, or something else?
could be the sahft seal. Did you turn the compressor 20 times or so to seat the seal? Many times a system leak will only show up under pressure. Try this....presssurize the system and place a plastic bag aroun the compressor. Wit overnight and stick a leak detecto probe in the bag and see if it goes off. I have a blank off plate for A6's that has fittings on ity. I pressurize the compressor and see if it holds. For the A6, a blank off plate is easy to fabricate.
I found that when I removed the A6 originally, it had a tablespoon or so of oil in at, at most. That, plus the test plate I made--that showed the compressor leaked--convinced me the compressor was the original source of my leak. I also made a plate to test the rest of the system, with the compressor removed, and it seemed to hold pressure, at least overnight, IIRC.
After replacing the seal, which I did lube, and putting about 9 oz of oil in the compressor, the system ran for maybe 45 minutes to an hour (in the driveway and on the highway), before pressure was low enough the compressor wouldn't come on.
Now not sure whether to open the system and try the test plate again--which may not tell me much if the seal needs more break-in time, or dump in more R134a and give it more 'time'?? :-)
I doubt that running more is going to help. If it still leaks at the seal, the seal may have been damaged during installation, or the shaft is not smooth. Leaking out in 45 minutes is a BIG leak.
Edited: Sat August 30, 2014 at 4:57 PM by mk378
Here is one of my test plates. I also have one with schraders in the fittings. Recover the chaarge, pressurize the compressor thru a plate, and then put the compressor in a plastic bag and seal it. After overnight, poke a hole in the bag and use a leak detector. If it's leaking, you'll know.
Edited: Sat August 30, 2014 at 6:48 PM by Dougflas
It'll test anything. The idea is to put the compressor under pressure while it is not on the car so you can (a) identify whether the car's leak is the compressor or "something else" and (b) if it is a compressor leak, have full access to the compressor to find exactly where the leak is.
The leak didn't happen in 45". That was the amount of time the system ran, in the 24-36 hours it took to leak down to a point it wouldn't cool well. Still sounds like a moderately big leak, to me?
Looks like I need to pull the compressor--AGAIN. Sounds like a good job for Labor day. Will let you know what I find.
The inner Teflon seal lip is the vacuum seal. The outer elastomer seal is the positive pressure seal.
A very smooth lip seal protector is recommended for the seal installation process. You might inspect the black rubber elastomer seal under magnification to look for damage
The A6 was not originally designed for a lip seal. The original mechanical face seal is more forgiving for shaft run out or excessive TIR due to tolerances or front bearing wear.
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
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