alswelke

2006 Suburban 2500 V8 - 6.0L 2WD. My AC quit working. We checked fuses all good. Switched relays and all good. Freon is good. We found that if we jump the ground on the relay the AC works fine. Take the jumper off and no ac. Looked at all ground wires and no cracks, breaks or loose wires. I cannot figure out how to get the air to work without the added on ground wire. Is there something else I should try?

tech2

the pcm supplies grd to turn on the relay to power the compressor... so what you have done is verified the relay and compressor works. What you don't know is why the pcm isn't turning on the relay.

briefly, jumper the low pressure switch. If the compressor turns on, the system is either low on refrigerant or the switch is bad.....how do you know the refrigerant level is good? the first thing to verify is the charge level; this should be done by recovering the system with an a/c machine...no other method is accurate. If the system is low...you have a leak. find and fix the leak...do not use sealer.

alswelke

Thank you for a place to start or I should say continue. I will try the above and post results.

alswelke

The switch on the accumulator has been jumped and the system did not operate. The static pressure in the system is 100 psi with the system off.
Also looking for a wiring diagram for the ac system for my suburban.

kevinkpk

I'd say you have an overcharge condition. As tech2 say's discharge the system, and replace with proper refregerant charge. The high side switch is probably locked the ac compressor out. Low side should be around 60, static

alswelke

I can do this too. But, we have had this suburban only for about 8 months and have not touched the ac other than to use it. The ac always ran perfect and very cold. It just stopped working one day. My question is would the high pressure switch lock and then unlock when we ground the relay?

tech2

by grounding the relay the way you are...you are bypassing all the other controls ...high cut off and low cut off. these sensors send input to the pcm...your cutting the pcm out of the equation.

alswelke

That makes sense. I am learning something here. Thank you. We are replacing both sensors today and will see what happens.

Pro Tow

alswelke

We have replaced both pressure sensors and the freon is at the right level. My question is: why is the PCM not grounding the relay? Do I have to replace the PCM or is there a way to test the PCM? When I ground the relay the A/C is ice cold and everything works.