No Power to AC Compressor

[251TwoDoor]

My AC compressor is not getting power and I do not have a clue why. So far I have had the compressor and system replaced last February (it has all worked fine since the install), have replaced the blower motor and resistor (worked fine after install), and replaced the AC control panel and replaced/serviced the plugs and wiring to the back of the panel. The old control panel had a burnt spot on it and the wiring and plugs to the back of the control unit had a few singed areas.

I though that once I replaced that wiring it would fix my compressor issue, but unfortunately it did not, and now I do not know where exactly to turn. I am currently in the process of finding wiring diagrams and seeing if I can manually route the flow of power - or the other option is to just wire a toggle switch directly to the compressor. I also think it could be something to do with the climate controlled switch that turns the compressor on, but I am not quite sure about that.

What do you guys think?

 

[496BBC]

what year and model is your truck?

First make sure the system is charged correctly, if low it will not complete the control circuit,

Try jumping the low pressure shutoff switch with a small piece of wire, the switch can go bad.

Neal

 

[251TwoDoor]

Thanks Neal. It is a 96 2dr Tahoe LS 4x4 and the system is fully charged with Freon.

Any idea where the low pressure shutoff switch would be located so that I can try this jumping method? Is there any risk of shorting something out or doing further damage by jumping the switch like that? Sorry if these are dumb questions, electrical diagnosis work is not my strong suite (not that I am unable to do any of it, I just do not have much experience with it)

 

[496BBC]

its on the firewall passenger side, on the accumulator its a 2 wire plug that unplugs from the switch.

 

[496BBC]

no risk of shorting anything out as long as you don't got to ground with it, it just passes positive side of 12 volts on to the relay.

take a small piece of wire strip the ends back and put into both the contacts of the plug you unplug from the switch.

 

[496BBC]

Have you checked the fuses for the AC to make sure they are not burnt?

 

[SAATR]

High pressure cutout switch could also cause the issue. It breaks the same circuit that the low pressure switch closes when pressure gets too high. It is possible that it has failed. Installing a jumper in similar fashion to the low pressure switch would bypass it. Best thing to do would be to check for power at the hot terminal of the switches until you find your problem. Broken wire is also possible. You should have unswitched power at pin 30 of the relay, ground on pin 85, and your pressure switch circuit and control head will apply power to pin 86 when the AC is turned on. If all of those check out, it could be between pin 87 and the compressor clutch.

Sent from my XT1585 using Tapatalk

 

[251TwoDoor]

I appreciate all of your replies guys - you really seem to know your stuff on these trucks. So based on the info you provided and a few google searches I know exactly what I am looking for to ID this plug and test using this bypass method. I will check it out tonight or tomorrow evening and keep you updated on what I find.

BTW: I found the thread below based on the info yall gave me before, and there seems to be a lot of good info there. Would you agree that it is pretty much the step by step breakdown of what to do and what the next step is based on the result?

Link to Forum Regarding GM Pressure Switches

Thanks again!

 

[251TwoDoor]

Also I have checked all of the fuses that show any connection to the compressor. I have also had some help to pin-check the voltage on some crucial wires in the AC system harness from the ECU/fuse block and everything checked out. We did not check anything on the accumulator side of the engine bay though.

 

[251TwoDoor]

UPDATE:
I bypassed the relay today with the help of a friend from work and the compressor immediately kicked on. We then swapped the relay with a new one I already had on hand and it had no effect, so the bypass wire is currently still attached on one end to the power box in the engine bay (the wire is removed for now to keep the battery from draining).

Could it cause any issues to run the truck like this until I figure out where the rest of my electrical issue is at, as long as I'm not pushing it or going high RPM? I live about 5 minutes from work and will only be on small and backroads.

We have a plan to hook a meter up and test a few other things, but it was not clear to me exactly what he was planning on checking and he does not have the proper meter with him today. I will keep this updated until we get it resolved. Thanks for you guys' help so far.