My brother hot-rigged Dad's 1986 240 A/C compressor such that he turns on a switch to start the compressor. It's all because the normal blue/red knob on the dash console doesn't start the compressor. I'm kinda fearful that the compressor won't know when to start and stop. I'm thinkin that the original design on the '86's was for the system to sense the evaporator outlet pipe temperature and cycle the compressor that way.

Also..I think there is a low pressure cut-out switch on the dryer...to stop compressor running without adequate refrigerant pressure.

We recently converted the system over to R134a...(flushed, vacuumed, and new parts)..but we didn't install a high pressure cut-out switch. Should we have?

What tells the compressor when to engage/dis-engage when the AC is turned ON?
Cabbie2169