Do these cars have a high pressure port? If not, you cannot check the high pressure, i.e. output of the compressor. So, how would you know it's dead other than to replace it? I struggled with this on my 93 940. My 93 940 has no high pressure port, I had a shop add one to a line, turned out my compressor was fine. With R134a you need to be charged pretty close to dead nuts for it to blow cold. Too little doesn't do it, and too much doesn't do it. Rebuilt compressors are at least 200 bucks.