Not the typical HVAC actuator issue...HELP!

[cousinjordo]

So I am all about scouring forums and finding what I need to know to fix the problem at hand. And I'm fully aware the HVAC actuator topics have been beat to death, but I haven't seen whats going on with mine described anywhere, so here goes...

2005 GMC Sierra Ext Cab, Z71, manual Dual climate controls (temp slide levers, turn dial for blower speed and mode select)

Last year, i changed out the blend door actuator for the drivers side, the one over the transmission hump. No problem. Typical symptoms, heat randomly on driver side, clicking sound...easy fix. Then, in August of this year, i smelled burning plastic from the vents, looked it up and found the blower motor resistor TSB. Local dealer fixed that for free. All good.

But now, something different is going on. 2 weeks ago, I got in my truck to head home and noticed the air conditioner wasn't on and my vents were blowing hot air. Tried turning on the a/c, but nothing happened when I hit the button. No light, nothing. I then realized nothing on the control unit responded at all except the blower speed. So, I went researching...best answer i could arrive at was i had a bad HVAC control module. I replaced that. No change, same thing. Back to square one.

Just for clarity, here's what is happening. The only thing that responds in any way is the blower motor speed and it does work on all speeds, so I don't think this is related to the resistor...I don't think? The A/C, Recirculation and Rear defrost buttons all are unresponsive (no lights, no function). The air is coming from my dash vents, blowing hot on driver side and just outside temperature air on passenger side. Even if I turn the blower off, when driving, the air still moves through the vents (unforced, blower is off) at the hot and room temps as I just mentioned.

I was able to unplug the mode door actuator, manually move the mode door to defrost and feet, so that provides a little relief from the hot air blowing in my face. However, if I plug it back in, as soon as it gets power, it automatically indexes back to the dash vent position.

Someone please help and tell me you have some idea of what to do. I don't want to take it to a dealer, but I am running out of options and none of the local part stores have a scanner that can read body/HVAC codes. Or if someone has a schematic of the HVAC wiring/could help me figure out how to diagnose the issue by checking voltages over on the passenger side panel where all the actuator wiring joins. Any help is appreciated!

[05Jay1500]

Have you solved this problem? My 05 Sierra with digital dual zone has recently developed a very similar problem. The difference with mine is that it blows cold air but only through the floor vents. Changing the settings for defrost or dash vents makes no difference.

 

Please let me know what you've found out if anything, and I'll do the same when I've figured it out.

 

Thanks very much.