Help! A/C techs!

[87chevy.com]

Originally Posted by hatzie

Clint,
The original factory part on a truck originally equipped for R12 is just an LPCO set for R12 refrigerant low pressure cutout.

The aftermarket replacements can be purchased with both HPCO & LPCO all in one. They're setup for R134a safety pressures so you kill 2 birds with one stone.

the r12 and r134a LPCO might not be different at all, the LPCO is there for 2 reasons, turn the power off to the compressor if there is lack of refrigerant - that would be a low pressure, and switch opens. the 2nd is simply to keep evaporator from freezing. the pressure nearly corresponds to evaporator temperature...
there might be some differences in the guts of the switch, but if the evaporate is frozen due to a improper LPCO switch, your going to cause high side pressures to shoot up and blow out of the relief valve in the compressor....

its not 2 birds one stone with that switch. Its a switch that can be installed either on high or low side and opens or closes based on internal guts - open or close... if you had 384 psi, in this sensors case, in your low side, i'm sure your evaporator would pop and fail as its normal operating pressures are around 120ºf just stting out in the sun baking (ambient temp) and lows of about 28ºf

https://www.aircomponents.com/produc...witch-f-r134a/

specs for that sensor
Female R134a 1/4 FF binary high-low pressure switch
low opens at 28 PSIG closes at 29 PSIG
high opens at 384 PSIG closes at 298 PSIG

high side switch should defiantly be installed on the high side line to prevent the head pressure from getting too much and letting the relief valve in the compressor let the refrigerant out.

clint