When I bought the car there was a sticker under hood that says it was retrofitted to R-134a. A/c has always worked fine. A few days ago I noticed a noise that sounded like the tab that scrapes the rotor when the brake pads get low, I think the sound was coming from the compressor and I noticed that the a/c did not work any more. After trying it several times it started working again and I did not have the noise anymore but the a/c stopped working again. I hooked up a cheap guage and it showed "GOOD" for refrigerant. I think that was the last time the compressor clutch came on. The fuse in fuse box is good. Not sure what I should do next. I think I will unplug the compressor, insert 12 volt tester, turn key on and see if I get any juice. Does car have to be running or key in on position good enough? Any help or suggestions would be appreciated in troubleshooting this issue.

You may want to read this article for information on clutch control and trouble shooting...

https://www.gmforum.com/t280192/

AC is reasonably detailed. Low pressure, high pressure, bad clutch, leaking hoses or seals, all can be a problem with the system. If the compressor isn't coming on,likely it'* not a connection issue unless you can visually see an issue at the wiring.