I went through hell getting the HVAC controls straightened out with my 80 633, there were wires cut relays missing etc. More to the point, check for voltage at the compressor first, if none my next step would be to check the thermostat for the A/C that hangs off the back of the heater control panel. If the capilary tube on it is kinked or broken or cracked it may not be working, check with a meter regardless. If neither of those things work I'd have to dig up the schematic I drew up when troubleshooting mine. Good Luck! Mike W.