This is a friend's car, A/C was blowing warm. Compressor wasn't engaging, though at-rest pressure was about 75 or so (I think) on high/low sides. A little low, to be sure, but not low enough to shut off compressor (?). Anyway, friend recently paid about $175 for top-up; I explained the only way to top up is if the system is low, which means there is a leak. Sure enough, I find oil slick around the fitting at the pressure switch. I jumper the switch, and system engages, then after some pressure has built I put the sniffer up to the joint and it goes off like crazy (and no, this is not the cheap Harbor Freight sniffer). So the fitting is definitely leaking, but the switch is also bad. When jumpered, the line quickly became cold.

Question - what is the switch called? We were calling around trying to locate one, and ran into several descriptions. I believe it is probably a low-pressure cutout switch, but not sure. It screws right into the accumulator canister. Any info would be appreciated.

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It seems from your description it is the low pressure cut out switch. It may be possible to replace with out a loss of refigerant, assuming the schrader fitting is not leaking. I would buy the new one from a GM dealer. recently I watched 2 of the chinese junk switches(new) cycle the compressor with less then 3 psi differential. If you have set of gages it would make the work easier. You would know if the system is operating ok. Good Luck.

If it's on the accumulator it is the clutch cycling switch. It controls the evaporator temperature by switching the compressor off when the low side pressure drops to a preset PSI. The compressor is switched back on when the pressure (and the evap temp) rises, usually 10-20PSI higher than the shutoff point.

If the system is low on refrigerant you get rapid clutch cycling because the pulldown happens too quickly.

This one sounds like the high pressure cut-in function is not working?

The last Ford I owned had a schraeder valve underneath the switch. Can't say whether the GM will be the same.

- JimY