How to verify compressor is normal on the desk

Tiny
XJSHEN
  • MEMBER
  • 2003 PONTIAC MONTANA
  • 3.4L
  • V6
  • FWD
  • AUTOMATIC
  • 72,000 MILES
My car A/C leaking was at low pressure A/C line connection to compressor, and high pressure line inlet to condenser where two o-ring was missing. I disconnected compressor, and A/C line fittings to rebuild system. I want to know how to determine a compressor function normal without leaking. I tested current circuit was on the compressor, but I do not know if compressor function is normal or leaking.
I am thinking to measure pressure on a compressor on the desk to see whether leaking place on the compressor using radiator coolant pressure tester (on the radiator), purge air into from one compressor end and lock another mouth with rubber cap, and see if compressor leaking occur.
If there is good way to test compressor leak on a table at disconnected state before install?
Thanks for your comment and instruction.
Tuesday, July 25th, 2017 AT 8:14 PM

6 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
Bench testing will not really tell you much with any pressures lower than the working pressure of the system because the only real place a compressor will leak is at the shaft seal. Those will always leak a small amount because of the way they function.
For that testing you need closer to 120 psi air to simulate the system pressures and a way to spin the shaft to see if the seal has any faults at operating rpm. Not something that is easy to do when on vehicle testing will show you much more.

A better option is to replace any o-rings with new and then test the system as installed. Vacuum it down and see if it holds. Then add a dye charge and the proper amount of 134A.
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Wednesday, July 26th, 2017 AT 8:57 AM
Tiny
XJSHEN
  • MEMBER
  • 246 POSTS
Thanks a lot! Your way is good. I will do replacement of all o-rings. But the dissect compressor and replace part on compressor is much difficult and is delicate professional work needs tools and techniques. Test its leak before installment is much easier choice if available. Once failed after install the un-teseted compressor with even replacement all the o-rings would damage new drier/accumulator/condenser since the three now as a combined set. Then there is no any way detect if compressor is normal without leaking before install to the system? Thanks!
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Wednesday, July 26th, 2017 AT 7:00 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
If the compressor leaks it won't hurt the other parts. The only way a compressor will damage the other parts is if it fails internally and sends pieces into the system. If it only leaks you can remove it, install a good unit and vacuum the system and recharge. Do it all the time.

Now if you think the compressor is bad internally, the best option would be to replace it. The compressor on that vehicle is very easy to get in re-manufactured or new if you think it has failed. If you were missing O-Rings ONLY and it leaked, the rest of the system can still be saved, Simply run a can of flush through the system, then air to clear it out, next pull a vacuum on it until you boil off any residual moisture. Recharge and enjoy the cold air.

As for testing the compressor for leaking, yes you can do it, but it takes an actual test bench which would cost more than replacing the car to buy.
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Wednesday, July 26th, 2017 AT 9:35 PM
Tiny
XJSHEN
  • MEMBER
  • 246 POSTS
After pool vacuum off for one hour, a/c system at -40 psi and the system hold the vacuum state for hours but when charging R134a, no R134a charged to the system since pressure meter showing still at minus pressure on the meter. Is it indicating the compressor does not work? Or other problem? I replaced new receiver/drier. Thanks for your help and instruction.
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Thursday, August 17th, 2017 AT 5:04 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
Check that the connector to the low side is OK and it is pushing the shrader valve in. Some of the valves seem to be a bit short and they don't open.
Also make sure the upper low side valve is open if you are using a regular gauge set, I've seen those stick before.
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Thursday, August 17th, 2017 AT 5:30 PM
Tiny
XJSHEN
  • MEMBER
  • 246 POSTS
Thank you so much. You are right. My Guage connector's pushing the shrader was in short that could not open the low side valve.
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Thursday, August 17th, 2017 AT 6:49 PM

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