Sam Franklin

Can somebody please help I've got a 2011 suburban system is charged but compressor won't engage its not getting signal to relay I can ground the trigger side of relay and it will engage

I can only find 1 pressure switch which is in the small line near the compressor it has 3 wires

repairman54

In my '11 Tahoe the HVAC module talks to the ECM . Low pressure cutoff reports to the ECM. ECM grounds the A/C compressor relay to activate it. That's what the schematic shows for my Tahoe. Have you done a full code scan, all 4 code families as just P codes will not show any HVAC or module communication issues as there may be a code helping to point the way.
Could be a dirty connection or ground issue, but knowing what a full scan shows is the first step.
There is also a evaporator temp. sensor that reports to the HVAC module.
Get a full code scan would be my best advise as that's what the dealer would do as the first step.

Sam Franklin

Thanks I have a harbor freight code reader that’s not showing any codes but have not had a real scan done I may take it to the dealer in few days and let them scan it

tech2

+1
the must be a inhibit reason for the pcm to not grd the relay.
how did you confirm the system is charged the correct amount?

Sam Franklin

I crossed out the relay engaging the compressor and had gauges on the system I don't remember the numbers now but was with in spec

tech2

pressure is not the most accurate way to determine charge level as its temp dependant. does your scan tool show a voltage for the pressure sensor? if yes...what is it.

so i'm confused....the pcm is grding the relay and t urning on the compressor or not? you providing the grd confirms the compressor, relay and all wiring except the grd control are good. the grd wire to the pcm and pcm control are still not known.

Sam Franklin

No the ecm is not turning on the compressor

and no my cheap scan tool doesn’t show voltage from the pressure sensor

but you have gave me some more things to check I didn’t realize the ecm was what tells it to turn on I’ve always worked on older vehicles that has low pressure cycling switch

Sam Franklin

I did lil more messing with it today and I’m getting power on 1 wire going into the pressure switch and the other 2 wires are grounded which I thought only 1 should be grounded

tech2

it probably correct. unplugged 5 on ref. o signal o grd

Sam Franklin

I only had a test light but it showed same with sensor connected or disconnected