AC compressor not coming on...

[malmed]

OK, a few weeks ago I installed a new AC Delco AC compressor, as a replacement to a bad one that was leaking after a year.... Last summer a new accumulator, condenser, expansion valve, seals, etc...
New compressor, all was fine for several days... had a separate issue, my lights would come back on after the 20 minute timeout... 1,4,10 minutes, but it would come back on... figured, ok bad switch, pulled battery, waited 2 days for new switch, replaced switch, did not fix it... noticed relay was extra warm, swapped relay, problem solved... OK, good...
Next day, no AC...
Compressor is not coming on...
jump low Freon switch, nothing... no 12 volts to compressor.
Swap Relay... still no joy.
Check power at relay, yep getting 12 volts there....
Bad ground? Run wire from neg on battery to block, still no joy.
Checked all fuses marked AC in any way, even swapped them all... still no joy.
Last resort, took a chance and replaced the climate control unit in the dash with a new aftermarket one, nope, no joy....

I'm out of ideas....
Anyone?

 

[LordWayback]

It sounds like a low R134A issue First I would get a DIY ac recharge kit and I would turn on the switch and pump refrigerant if it’s below 30 psi aka low pressure it will not send voltage unless you jump the relay I would Check your pigtail mine was so chewed up on the high pressure switch not even a replacement plug would fix it so I had to bypass my high pressure switch or no ac. Yes a relay jumper isn’t the proper way to fix something but if a relay is hot there’s a wire break/resistance jump such as a relay turning on and off often which would happen with low Freon if it starts pumping with the jumper then it’s wiring/low r134a.

 

[rockola1971]

Do you have access to a decent scanner to tell what state the low and high pressure switches are at? The compressor clutch relay is GROUND SEEKING. The PCM provides that ground when conditions are met. The IGN E fuse (10a) provides 12v to the clutch RELAY COIL. The AC clutch itself is BOTH ground and 12v seeking. The 12v is provided by AC COMP fuse (10a) and that 12v has to pass through the closed Compressor clutch relay. The ground itself to the compressor clutch is provided by the HVAC control module BUT the ground has to be able to pass through the low pressure which will be opened up if refrigerant pressure is much lower than 30psi or so.
Quick and dirty is stick a set of refrigerant gauges on the hi and low side. The pressures should be roughly the same which is what happens when any a/c system is off. Id be interested in what pressures you read on yours. Common mistake after servicing an A/C system is not to make sure the valves in the schrader valves are tight, esspecially on the low side. A hose and gauge set can loosen the low side easily. I also recommend replacing the valves any time the system need to be evacuated, pumped down and recharged. Its cheap insurance.

 

[malmed]

My mechanic that is helping to try to solve this had put it on his scanner, I have messaged him to see what he says about low and high switch states....
He had to put my truck on the back burner for now as he had other jobs promised... but he is a 65 year old fella thats been doing AC work a long time... and he is stumped.

Jumping the low pressure switch does nothing... I do not know about the high pressure switch.

It sure seems like it would be a electrical component failure as this happened after I pulled the battery, before I did that it was working fine for many days after the new compressor....
Even if there was a leak and all Freon was lost, jumping the low should make the compressor kick on, and it does not....

Do you have access to a decent scanner to tell what state the low and high pressure switches are at? The compressor clutch relay is GROUND SEEKING. The PCM provides that ground when conditions are met. The IGN E fuse (10a) provides 12v to the clutch RELAY. The AC clutch itself is BOTH ground and 12v seeking. The 12v is provided by AC COMP fuse (10a) and that 12v has to pass through the closed Compressor clutch relay. The ground itself to the compressor clutch is provided by the HVAC control module BUT the ground has to be able to pass through the low pressure which will be opened up if refrigerant pressure is much lower than 30psi or so.
Quick and dirty is stick a set of refrigerant gauges on the hi and low side. The pressures should be roughly the same which is what happens when any a/c system is off. Id be interested in what pressures you read on yours. Common mistake after servicing an A/C system is not to make sure the valves in the schrader valves are tight, esspecially on the low side. A hose and gauge set can loosen the low side easily. I also recommend replacing the valves any time the system need to be evacuated, pumped down and recharged. Its cheap insurance.

 

[malmed]

Bad PCM that didn't show up until the battery was disconnected???

 

[rockola1971]

Bad PCM that didn't show up until the battery was disconnected???

There are actual codes for bad PCM but one output (The a/c in this case) could be opened up and may or may not cause a CEL for a bad PCM. I would be more inclined to check for a wiring problem or connector problem. Pull the plugs at the PCM and inspect for corrosion and clean.

 

[malmed]

OK, today I disconnected the PCM, connections look clean, shot em with cleaner anyway... I disconnected the negative terminal, touched it to the positive a few times to clear things, waited 30 min, reconnected everything... still no joy, compressor does not kick on at all. later week my mechanic buddy with the scanner will dive back in.... thanks for the advice.... I will post when and if I get this one figured out....

 

[jwth]

I had a similar problem with my 2003 slt and took it to a shop where they replaced valves and compressor with no joy.
They said they were stumped and could not fix it so no charge.
I did find a youtube that showed an AMBIANT OUTSIDE AIR TEMPERATURE SWITCH located behind the right hand head light assembly stuck to the inner fender plastic. Cost 15 or so dollars, checked between the two for resistance differences and the old one was open so plugged her in and been running good since.

 

[malmed]

AMBIANT OUTSIDE AIR TEMPERATURE SWITCH located behind the right hand head light assembly stuck to the inner fender plastic. Cost 15 or so dollars, checked between the two for resistance differences and the old one was open so plugged her in and been running good since.

I ordered one, can't hurt to try, they are pretty cheap... and I have noticed the readings on the mirror sometimes are gone, and sometimes are wrong.

 

[malmed]

OK, I finally solved this, to help any future people with the same issue....

It was just out of Freon, a leak.

My mechanic said he could not get voltage to the clutch no matter what he did and it would not engage by jumping the low pressure switch....
So, I took it to a retired X auto electrical man, to investigate the wiring....
He threw a can of Freon in and compressor kicked on just fine.
So I brought it home.

I found a loose shraider valve on the new accumulator... tightened it, pulled a vacuum, it held vacuum for 6 hours, so I decided that was it....
Filled it with 3 lbs of freon, figure I didn't lose any oil being where the leak was....
40 degree air.
3 days later 40 degree air.
Fingers crossed....

Thanks for the info, advise, and help guys....