05 Yukon auto A/C control question

[chevytruckluver]

I just bought an 05 Yukon with the Auto A/C control. The a/c doesn't work. The clutch doesn't engage and the digital display on the auto control doesn't light up at all . The blower works and the air will move from floor to dash to windshield but is always hot only. Can anyone tell me where I should start? I'm thinking the control head will need to be replaced anyway because it has no display at all. Just wondering if this could also be why the clutch doesn't pull in?
Thanks

[EVRLET]

Isolate is the key to troubleshooting.

Go to the fuse/relay box under the hood and pull the ac relay. Now grab a wire and jump 30 and 87. Engine or key doesn’t have to be on. Does the clutch engage? If so, then you know the compressor is good.

Grab your AC gauges and hook them up. Do you have pressure or are they at zero with the valves open? If you have pressure, then at least you know you don’t have a leak. Depending on pressure amount, you may have had a small leak, big leak, or no leak.

Now you said the HVAC controller doesn’t light up, but you can obviously turn on the blower motor. However that doesn’t mean the controller is 100% operational. The controller, when you turn the ac on, sends the signal to leg 86 of the ac relay you pulled out. This turns the relay on and connects 30 to 87. This is why you test the compressor to isolate.

There are other things like ac high pressure and low pressure sensors that affects ac compressor turn on. However, with all the ac issues in these SUVs and Silverados, many times it’s been the relay, controller and/or compressor.

Now once you get the ac system turning on through the controller, then you can deal with blend door actuators.

That should be enough to start you off.

[chevytruckluver]

Originally Posted by EVRLET

Isolate is the key to troubleshooting.

Go to the fuse/relay box under the hood and pull the ac relay. Now grab a wire and jump 30 and 87. Engine or key doesn’t have to be on. Does the clutch engage? If so, then you know the compressor is good.

Grab your AC gauges and hook them up. Do you have pressure or are they at zero with the valves open? If you have pressure, then at least you know you don’t have a leak. Depending on pressure amount, you may have had a small leak, big leak, or no leak.

Now you said the HVAC controller doesn’t light up, but you can obviously turn on the blower motor. However that doesn’t mean the controller is 100% operational. The controller, when you turn the ac on, sends the signal to leg 86 of the ac relay you pulled out. This turns the relay on and connects 30 to 87. This is why you test the compressor to isolate.

There are other things like ac high pressure and low pressure sensors that affects ac compressor turn on. However, with all the ac issues in these SUVs and Silverados, many times it’s been the relay, controller and/or compressor.

Now once you get the ac system turning on through the controller, then you can deal with blend door actuators.

That should be enough to start you off.

Thank you that gives me a great start! I will see where it takes me..