I now think many of my issues were a short between the headsets. But I decided an update was in order. I replaced the original compressor with a 508, made and/or adapted a few hoses, and all is well.

What is 121?

Are you assuming it is just overcharged?

I have a 73 Mustang Mach 1. I got the car about thirty years ago. It had AC stock but I got it with no engine. So I pieced the AC together and charged it with R12. I got a 30# cylinder back when it was available. I still have about half of it. The car has not been used much the last few years. I am ...