A/C not working

[Hobbyist4Life]

Hello,

The car is a 2006 GMC Envoy XL Denali that I bought from a scrapyard.

There is refrigerant in the system. However, it seems like the HVAC control module is not giving the command to engage the compressor.

I tried supplying 12v to the clutch and it engaged! So I just need to figure out why in the world is it not being commanded to turn on.

The fuse and relay are tested and working, just the relay not getting the signal.

Thanks in advance!

Regards,
H3L

 

[m.mcmillen]

The question would be how much is in the system. It could be low enough that the low pressure switch is keeping it from engaging. Or, it could be a faulty low pressure switch. Your best bet would be to get a set of gauges on there and see what is going on.

 

[Hobbyist4Life]

It's not the low pressure sensor, I have tried to short out the connector and it still didn't engage

 

[budwich]

you are good with "shorts"... now get a meter and check what is happening in the circuit... especially with the AC relay since without it operating, nothing is going to make "noise" in "AC land".

 

[Mooseman]

Could also be a bad relay. Try swapping it out with another.

The PCM commands the relay for the compressor, not the HVAC module. However it does send a signal to the PCM that A/C is requested. The PCM decides if the conditions are right to engage the compressor.

There is also the high pressure switch that could be defective. Can't remember if it's a "normally open" or "normally closed" switch. Check the schematics.

Ensure that there is continuity from the PCM to the relay. You did check all the fuses with a DMM, right?

 

[mrrsm]

A/C Manifold Gauges... FTW... (1:35)

 

[budwich]

Could also be a bad relay. Try swapping it out with another.

The PCM commands the relay for the compressor, not the HVAC module. However it does send a signal to the PCM that A/C is requested. The PCM decides if the conditions are right to engage the compressor.

There is also the high pressure switch that could be defective. Can't remember if it's a "normally open" or "normally closed" switch. Check the schematics.

Ensure that there is continuity from the PCM to the relay. You did check all the fuses with a DMM, right?

The "high pressure" switch isn't a switch per se, its a pressure sensor which is read by the PCM.

 

[Hobbyist4Life]

I'm sorry, but this thread has to be postponed until I fix the major problem with the brakes!!

Basically, the car doesn't stop, period.

Edit: I have already tried switching out the relays and yes, all the fuses have been checked!

 

[Hobbyist4Life]

Update!

The car still doesn't stop. However, it turns out one of the A/C hoses for the rear evaporator was loose near the firewall.

Someone must've opened it and couldn't tighten it up properly due to lack of space. The garage bent one of the spanners in order to tighten it properly.

Got the system checked for leaks, and recharged it after approval.

But I feel like the driver's A/C vent in the center console blows less air, any inputs?


The car is now at the stealership to figure out what the problem is with the brakes

 

[Hobbyist4Life]

Update!

With the brakes out of the way, the A/C only lasted less than a quarter of a day (suddenly stopped when checking the operation of the brakes).

Went back to the shop and been told the belt got cut. It sounded logical to me since the vehicle hasn't moved since late 2011 and at some point went to the scrapyard where I found it.

When I decided to approach replacing the belt, I found that the belt is not fine, but worked it's way out of the pulleys. While attempting to re-seat it, I noticed the compressor is actually not bolted to the engine

Went to a scrapyard and digged up the required 4 bolts, but I couldn't raise the compressor up enough in its place for the holes to line up. After reaching in there with my phone's camera, it turns out the compressor bracket was actually broken. I suspect that since the lower 2 bolts are missing, all the load was on the bracket's top 2 bolts and snapped clean off.

after getting it replaced and recharged the system and got the brakes in working order, I have an issue with some vent's actuator. Not sure which one yet, but I'll just leave that for later.

My real concern is the A/C doesn't seem to cool at idle. when stopped, if I hold the RPM at 1k it will blow cool air.

I know for a fact that the engine cooling fan's speed sensor is not working. but AFAIK, when the ecu doesn't receive fan speed signal it commands full speed all the time. I can also hear the fan running when I rev it up at idle.

What could be the issue? could it be the compressor?

 

[TJBaker57]

Fairly normal for auto AC to struggle at Idle and no vehicle motion. (Stopped). As far as I know the ECU does not command full speed with lack of input from speed sensor. Most likely the fan clutch may be going or gone. Mine ran that way for years with no appreciable harm done.

 

[Mooseman]

Likely the fan clutch is toast and just freewheeling.

How to test the electro-viscous fan clutch

 

[Hobbyist4Life]

Fairly normal for auto AC to struggle at Idle and no vehicle motion. (Stopped). As far as I know the ECU does not command full speed with lack of input from speed sensor. Most likely the fan clutch may be going or gone. Mine ran that way for years with no appreciable harm done.

When I first read this, I was very sure that it wasn't the situation as I'm pretty familiar with how much it should cool at idle. I had an '05 TB LS that I had repaired it's A/C system myself.

Likely the fan clutch is toast and just freewheeling.

How to test the electro-viscous fan clutch

Thanks for the input, but the fan clutch is either seized on, or being commanded full speed by the ECU as I stated earlier. I'll be testing this by pulling the connector and checking if it's still loud.


As for the A/C issue, I've had it repaired at the dealer. I've been informed that the refrigerant is low when I was fixing the front differential oil leak at a shop, and got it topped off. A couple of days (literally) later I take it to the dealer to diagnose a hard shift from 1st to 2nd (which turned out to be the input speed sensor, as I speculated) and they checked the refrigerant and told me it was low (srsly??) so they checked for leaks and turns out that it was leaking by the expansion valve.

Got that sorted out and the A/C is blowing ice cold ever since!