2003 Suburban: no voltage at the low pressure switch. I've checked all fuses and the relay that I can find, still no power. Any ideas?

 

the hvac module should supply 5v ref to the switch on the dark blue wire when the hvac is turned on. When the system has a refriderant charge and commanded on, the switch grounds this voltage so it will read 0volts until you open the circuit. Are you disconnecting the low pressure switch when you test it for voltage?


So if you did test with the switch disconnected and has 0volts, and the fuses for the hvac module are ok...check for power at the hvac module at connector 1 pin A12 dark blue wire.

do the other hvac controls work? there are 3 havc fuses that I can think of.

 

Thanks for your reply!

I am just using a test light at the switch with it disconnected. Will it light up with only 5v?

Yes, all the other controls seem to be working properly.

I will check the HVAC module and report back.

Thanks again!

 

I've been away and on another project.... But I just used a meter on the low-pressure switch and have 4.97v, so I'll move on down to the hi-pressure switch and see what it's reading. Am I correct that it should be 12v there? Also, if it is bad, do I lose pressure / freon if it is replaced?

Thanks, again, for your help!

 

does the system have a full charge? I would start there.

 

Is there a way to tell if it's fully charged with the compressor not engaged?

I have just checked the power to the hi-pressure switch, and there is none. I'm in the process of going through every fuse in the panels to see if I've missed something somewhere.

Thanks, again!

 

the first step of a/c diagnosis is to verify the system charge level. forget about testing anything else until this is verified.




with the system on, briefly jumper the low pressure switch. if the compressor engages your probably low on refrigerant. the proper way to verify charge level is to recover the system. Without a a/c machine, a pressure guage on the service port would work ok when you correlate the psi with the ambient temperature.