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leaks under pressure but not vacuum?

tab a on Sat August 30, 2014 9:23 AM User is offline

Year: 1987
Make: Jaguar
Model: XJ6
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?

Thanks.

TB

Dougflas on Sat August 30, 2014 10:52 AM User is offline

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.

wptski on Sat August 30, 2014 11:32 AM User is offline

Quote
Originally posted by: tab a
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?

Thanks.

TB
I ran into almost the same thing except mine was driven once, sat all winter and found a puddle of oil this spring. I found this thread here. Look at the post from "iceman2555". I asked for more details in my thread but the user never returned this season, I guess.

I got a nitrogen setup, pressurized to 150psi, it held and vacuum held as well. Charged it up and drove it as much as I could but it's a family backup. So far so good!

Edited: Sat August 30, 2014 at 11:33 AM by wptski

wptski on Sat August 30, 2014 1:36 PM User is offline

Quote
Originally posted by: Dougflas
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 was thinking of making a test manifold plate for my HR6 if it leaked again.

tab a on Sat August 30, 2014 2:01 PM User is offline

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'?? :-)

Thanks again.

TB

mk378 on Sat August 30, 2014 4:56 PM User is offline

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

Dougflas on Sat August 30, 2014 6:47 PM User is offline

test plate

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

wptski on Sat August 30, 2014 8:06 PM User is offline

Quote
Originally posted by: Dougflas
test plate

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.
If it's possible that a new seal can leak as I pointed to above or does is that for testing bad leaks on new seals or used seals?

mk378 on Sat August 30, 2014 8:56 PM User is offline

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.

wptski on Sat August 30, 2014 10:51 PM User is offline

Quote
Originally posted by: mk378
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.
True, it'll test anything but is it being used on a new seal which can leak anyway till it's run in? Doesn't sound like it's being used on a installed compressor since it's put into a plastic bag overnight.

Dougflas on Sat August 30, 2014 11:36 PM User is offline

Quote
Originally posted by: wptski
Quote
Originally posted by: mk378
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.

True, it'll test anything but is it being used on a new seal which can leak anyway till it's run in? Doesn't sound like it's being used on a installed compressor since it's put into a plastic bag overnight.

He has already replaced the seal. He will be testing to see if the new seal is leaking. He has said that he has run the system. If one is to use the plastic bag and test plate after replacing a new seal, just turn the compressor shaft 15 to 20 revolutions. It should seat.

wptski on Sun August 31, 2014 8:09 AM User is offline

Quote
Originally posted by: Dougflas

He has already replaced the seal. He will be testing to see if the new seal is leaking. He has said that he has run the system. If one is to use the plastic bag and test plate after replacing a new seal, just turn the compressor shaft 15 to 20 revolutions. It should seat.
If all one needs is 15-20 revs, you'd get that during the charging process "probably" and a far cry from the 8-10 hrs that "iceman2555" mentioned in that old post. The HR6 that I rebuilt, I turned the shaft after oil was installed, let it sit shaft down, used it only one time, sat all winter and had a puddle of oil come spring. I have no idea when it leaked. It held 150psi of N2 for days, evacuated using a micron gauge, never got above 1700 microns for days something one can't even see on a analog gauge. A R134A conversion took the weighed in 90% charge all on the high side. Ambient in low eighties, vent air down to 35F which freezes me out in max. Drove it instead of my other vehicle and so far no oil in catch pan but can't say if there is a small leak yet. Not seeing any oil leaking yet seems to be a radical change or improvement to me.


Edited: Sun August 31, 2014 at 8:12 AM by wptski

tab a on Sun August 31, 2014 9:19 AM User is offline

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.

Thanks.

TB

ice-n-tropics on Tue September 02, 2014 9:30 PM User is offline

TB
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.
hotrodc

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