2011 GMC 2500hd HVAC not working correctly

DavC · November 1, 2019

Auto hvac (and in manual mode) does not blow air (hot or cold) out of either side, top or bottom.

When truck is started (hvac in auto mode) airflow works correctly. But after the inside temp reaches selected temperature the air flow stops (as normal) but when the cab temperature changes (up or down) and heat or cold is called for, no air blows out anywhere. But the fan does come on and you can hear it blowing.

From what I can tell there are multiple actuators that control air flow. I am finding it difficult to determine how many there are and what they control. I know there is one in the middle (behind the kick plate) and one on the left (driver side). I think there may be another on top behind the glove box, that I believe controls the "recirculation" door, but I haven't removed the glove box to look.

I am wondering if the recirculation door not working would cause no air to be blown through the hvac box.

Does anyone know:

How many actuators there are.

What each is called and what they control.

C/K Man · November 5, 2019

There are 4 actuators. The mode (defrost/dash/floor) is on the left side of the HVAC module above the accelerator pedal. It has a large cam on it to move the dampers. The left temp. actuator is on the bottom center of the HVAC module, above the transmission tunnel a bit to the right behind the lower sound insulator. The right side temp. actuator is on top of the HVAC module, roughly in line with the left (lower) temp. actuator. That one is tough to get to. The fresh/recirculate actuator is all the way on the right side above the fan housing. To get to that one you usually have to remove the right air bag and/or glove box depending on which dash you have. I have never experienced the problem you are having, my guess is that it is either the fresh/recirculate actuator or maybe the HVAC control module. I would take a look under the dash on the right side to see if a plastic bag or piece of paper got sucked up into the recirculate air intake.

HawkScot · November 7, 2019

You might try unhooking the battery for 30 minutes or so.. then hook it back up and see if it changed anything..

captadamnj · November 8, 2019

My experience with actuators is that they can other get out of index, meaning they "lose track" of what full open and closed ar, and thus wind up in the wrong position what the HVAC control calls for. Alternatively, they can just completely fail and stop responding completely. The actuators can re learn correct positioning by disconnecting the battery, or sometimes just pulling the HVAC fuse from the fuse box. This can also be accomplished at a dealer with a tech ii tool.

I had manual controls in my LBZ, had to replace the HVAC head unit 2x in 11 years. But when it didn't work, a function completely stopped working, it wasn't intermittent.

DavC · November 15, 2019

thanks for replying. I have tried pulling the fuses as well as unhooking the battery in hopes that it reset itself. However that didn't make any difference. This still occurs intermittently.

I haven't had time to mess with it or think about it lately. Guess I may end up having it diagnosed by the dealer as I hate guessing and just throwing parts at it.

When I get it figured out I will post back. Hopefully it will help someone else some day.