Pontiac Repair: Air conditioner for 1995 Pontiac Firebird, pontiac firebird, salvage yard

Question
Harold,
My wife purchased this 1995, Pontiac Firebird with it's 3.4 motor new.  The air conditioning was never cold but it always worked.  On hot days it just couldn't keep up.  Last summer season the air didn't work but we didn't use the car enough to justify looking into it.  This year I thought I understood the problem and set out to fix it.  The clutch on the air compressor wasn't kicking on when you turned the air on.  The fuses were all good so I went to the salvage yard and bought a used compressor with clutch.  I put the first one on, turned the air on and the clutch engaged.  I began putting coolant into the system and the clutch froze up.  When I let the coolant back out the clutch worked agian.  I took that copmpressor back and tried two more. Neither of those worked at all.  The last thing I tried was to purchase a remanufactured compressor, with clutch, from a parts house.  I thought that since one of the compressors from the salvage yard had acted like it wanted to work that the compressor was the problem.  I am using the correct coolant and oil specified by GM.  I don't know what to try next.  Any suggestions that you have would be appreciated.
Thanks
Doug  

Answer
Just because the clutch does not engage does NOT mean that the compressor or clutch is bad. There are several pressure switches in the AC system that will not let the compressor turn on due to high or low system pressures. They are safety devices that are there to stop the compressor from being damaged.
I would suggest that you take it to the dealer and have it diagnosed before you throw any more parts at it.