What is this called?

[manger]

I'm asking about the switch in the middle of the pic. low pressure switch? temperature control switch? with 20 psi in the ac system should i get conductivity through the switch or should it be closed?

 

[Yellowsplash]

Low pressure switch

 

[Scotty J.]

should i get conductivity through the switch or should it be closed?

Just for clarity, a closed switch conducts, an open switch does not conduct.

(sorry, just anal about things like that).

 

[kimcrwbr1]

It depends on the system but I believe it is the clutch cycling switch it keeps the pressure within 25-35 psi too little pressure the compressor clutch wont enguage to protect the compressor and as the pressure gets above 35 it cycles the compressor to prevent freezing of the evaporator coil in the cab. A good rule of thumb on charging is to get 20 degrees delta-t measure the temperature going into the blower motor and the temp coming out the vents slowly add refrigerant until the difference is 20 degrees and run the system about 10 minutes after each time you add or remove refrigerant for the system to stabilize. If the system is dead as in no pressure you need to fix the leak dont just add refrigerant as a single drop of water will destroy the compressor and with a dead system the chance of water being in there is pretty good.