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What is wrong with the system?

bob2009 on Fri June 12, 2009 11:50 AM User is offline

Year: n/a
Make: n/a
Model: n/a
Country of Origin: United States

What is the root cause for this issue:

with the ac compressor off: low and high sides have the same pressure reading.
with the ac compressor on: low side is at lowest vacuum, high side has twice the pressure.

I am thinking of a bad compressor, but a friend says it is a bad expansion valve.
Whos is right?

Side note: system has no leaks. It holds vacuum well.

mk378 on Fri June 12, 2009 12:01 PM User is offline

I agree with your friend. There is a blockage. TXV is most likely but condensers and receiver-driers can also get blocked.

Also you can see the low side go into vacuum on a system that is badly undercharged, but otherwise OK.

Compressor is doing its thing just fine-- its job is to make the low side lower and the high side higher.

Edited: Fri June 12, 2009 at 12:04 PM by mk378

bob2009 on Fri June 12, 2009 12:19 PM User is offline

Well, the receiver/driver is new. If the there is a blockage in the TXV, then why do both sides show the same pressure reading, when the compressor is off? I was thinking that the low side would stay in vacuum.

mk378 on Fri June 12, 2009 1:14 PM User is offline

Eventually, pressure will equalize as the valve may not be completely blocked. It is also possible to normally have slow leakage backwards through a good compressor after it stops.

Pressure with the compressor off should be equal to the saturation pressure of the refrigerant at your ambient temperature. This means that there is at least some liquid refrigerant in the system.

Chick on Fri June 12, 2009 6:08 PM User is offlineView users profile

You have to think of the compressor as a pump.. It draws in (which it's doing as shown by going into vacuum) and pumps out (which is shown by the high side pressure) so your compressor is working.. As mk378 stated, thats a sure sign of a blockage providing you had enough refrigerant in the system, and guessing that the high side was over say 200psi??? you could give us the year, make and model of the car, and what the original problem was, and we can help you a little more.. Hope this helps..

Email: Chick


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