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AC Compressor

dancewithyou on Sun August 23, 2009 3:14 AM User is offline

Year: 1991
Make: Chevy
Model: C1500
Engine Size: 5.0
Country of Origin: United States

I am working on a friend's '91 chevy pickup. She took it in to a shop and had a "ac system check" done on it. They said it was just low on freon and needed the valves replaced. When I looked at it, it was very low on freon (actually no freon). we replaced the valves and the orifice tube (it was very full). It still won't take a charge. we blew out the condenser with no problems or anything coming out. We then blew air through the system the other way (ie. through the compressor) and that also blew through cleanly. My question is, shouldn't we have been unable to blow through the compressor? It seems to me that the compressor has to be a positive displacement pump and therefore shouldn't allow air to pass either direction when it's not turning. If so, that would tell me the compressor is shot, right? BTW, when we blew through the system we used regulated air pressure of 45 psi so as not to damage any seals.

iceman2555 on Sun August 23, 2009 6:14 AM User is offlineView users profile

Not quite sure what is meant by the term describing the orifice tube.... 'it was full' ! Does this mean that the tube filter screen was heavily contaminated ?. If so, then the compressor has failed internally. This is not an uncommon problem with vehicles that have been operated with an insufficient (low charge) of refrigerant. This is often more indicative of system that have been incorrectly retro'd to 134a. Most of these retro's are seriously undercharged to rectify a perceived pressure problem.
If this is indeed the problem, then the compressor will need to be replaced. The system flushed and cleaned thoroughly. A new orifice tube, accumulator, the correct amount and type of PAG lubricant installed, the system evacuated and recharged.
Blowing air thru a condenser is not a valid test for possible restrictions. Pressure/temp testing is a valid test for determination of possible condenser restrictions.

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