A/C works great at times, blows warm air at other times. Has the original R-12. No unusual noises. Can this be a relay problem? 2 relays side by side under hood on left front fender. I know one is the compressor relay. What is the other relay, and which is the compressor relay?

 

the other relay is for the condensor fan .the compresor relay has a red wire in it....To answer your question yes it could be a relay problem but it could also be a lot of other things,,,,,,,,

try this....when a/c cuts out , car running, you need to chk if you get power at relay black/yellow wires there are 2 and both should be powered...if so, chk if you get ground at red/blue wire. if so, most likely u got a bad relay ,,,to confirm it , jump the black/yellow and red wires together if compressor engages you got a bad relay ...
Now if you dont get power at black/yellow you got a wiring problem since we know that the fuse is ok because it works at times ...

If you don't get a ground at red/blue ..there is a problem on the ground circuit and could be a **** load of things ,,,,,,but if don't get ground give it ground from any body ground to red/blue at relay see if compressor engages

also chk the a/c clutch gap if way too big it makes a/c cut out as well

try these test and let me know