Hello all.

This is my first post in this forum. Please excuse me if I am posting in the wrong place or making duplicates. I have googled and I can't find answers.

I have a new-to-me 2004 Chevrolet Suburban Z71 with the Bose package. This is my problem:

Does Not Work:
- Rear / Aux Hot/Cold control dial
- Rear / Aux Floor / Ceiling vent selector dial.

Does Work:
- Rear Blower
- Rear AC Blows Cold
- Rear Heat Blows Cold

What Have I done so far:
I thought the problem was the blend door actuators behind the rear/passenger trim panel. I pulled that off and replaced both. Nothing changed. During that process, I manually flipped both blend door actuators with my fingers. When I flip the spindles with my fingers I can get hot air or cold air from both the ceiling vents and the floor vent so I know all that works. I know there's a part called the HVAC control module. Usually it's mounted behind that same rear/passenger panel between the two blend doors. My model does not have this part in this location. It's not there and there are no free wires/connectors that I can see. I believe this part is discontinued and replacement used parts seem expensive. Where is this part on my model? I attempted to relearn/recalibrate the blend doors by disconnecting the battery and setting the dials to heat, reconnecting the battery, and waiting for the computer to recalibrate. I checked the RR HVAC fuse. I didn't test it with a meter but it looked fine visually. The front HVAC works great, cold and hot. Another piece to the puzzle is that the previous owner changed out the stock radio and there's some weird quirks - the radio plays sound only after the door chime sounds. I haven't dug into that yet. Could that somehow be integrated into this rear AC problem? Maybe is a wiring problem?

In summary:
What's the diagnosis if it's not the blend door actuators? Is there a fuse I should check? Where is the part that I need located if it's not behind that rear/passenger trim panel?

Thank You. Go at it!

 

Do both the front dash controls for the rear and the back seat dash controls act the same way?

 

Yes. To clarify, the front HVAC controls function properly. The front controls for the rear HVAC act the same way. The blower dial 0123 works fine. The temp dial does not function. The vent selector does not function. When the front control is on Aux, the rear control acts the same. The blower dial functions, the other two do not.

 

Ever find a fix for this? Having same issues with my 05 Tahoe. Replaced both blend doors and still nothing. Also tried several used control modules with no change.