I don't know for sure on your 65 but most cars turn the a/c compresser on when in deforst mode [ air coming out of top vents] It should not do it in heat mode, but then air would not be coming out of top vents. Check control position and adjustment ??
Only things I can think of would be to chech the connections that you can get to (electrical) for corrosion, then look for a vaccuum line that is off or leaking. Seems odd that a vaccuum leak would stick the compressor 'on', but vaccuum controls are mostly voodoo and witchcraft anyway. There is also a vaccuum manifold in the heat/air control on the dash (guessing on '65) that controls the doors and blender, those are bad about leaking and just falling apart. As a temp fix, you could remove the belt for winter.
If the compresser shuts off when you turn off the blower motor, Then your compresser and clutch are working normal. I would look at the switch on the defroster that would normally turn on the a/c when you use your defroster. I am not sure where that is on your car. Your shop manual should show it.
gettin there, you are pulling me through the keyhole. To paraphrase, when the lever at the dash on moved to AC it closes a switch sending 12V to the compressor. But those volts stop along the way to get a final go-no go signal, from the pressure cut off switch.
So if my compressor keeps running the problem will not be in the pressure switch, because I can see the compressor coming on and off. It will be in the dash, where the circuit is staying closed even when I move the lever?
Just to be sure on the lever, do you mean the top lever which is the cable, or the bottom lever, which is the vacuum hoses?
It would appear the thermoststic switch combines the activation from the cable and the sensor into one unit.
I pull the lever over to HEAT and the clutch continues to engage/disengage as it nothing happened. When I pull off one ot the switches wires, the clutch stops. So I think I have found the culprit, don't know where to get a replacement though.