MY 1975 corvette is having an issue with the AC (R-12), I have 12 volts to the low-pressure switch and maybe 1 volt on the other side going to the compressor, I ohm the switch and it shows it’s closed, but no voltage flows through the switch.  I was going to replace the low-pressure switch but the replacement switch is printed on it that it’s for a R-134a, will this work with R-12?  If so, is there a check valve in the system to allow me to change it and not lose my R-12 that’s in the system if any?

I also checked my compressor clutch by applying 12 volts directly to the compressor and the clutch in gages as it should.

Thanks Jeff