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Discussion Starter #1 (Edited)
So im not 100% sure what the actual name of it is called, but when I turn the ac from face to feet, it sounds like the mode door is just flapping back and forth if that makes sense.. Anybody else have this issue on a 2007 tbss?

06'TrailblazerSS, 07'Z06,71'Stingray
322 Posts
Mine has never made the flapping noise that you mention. However, it has had the situation were it blows hot up top and cold down below. Also cold on drivers side and hot on the passenger. The truck is an 2006 SS. Believe it or not both times it did it on a short 2 hour drive and upon reaching the destination and unloading. Then restarting it acted normal again. I agree the search function here is not the best. The guys here are typically very helpful. I hope someone chimes in who has made the appropriate repair. Good luck. Mine has 128,000 miles.

2008 TrailblazerSS
292 Posts
"cold on drivers side and hot on the passenger ". This is the problem I have a few times during the cold weather. It has always fixed itself after a few restarts, so it's not a big enough problem to tear the dash apart.



Calibration Procedure

Use the following steps to perform the calibration update:

Turn OFF the ignition.

Remove the battery positive voltage circuit fuse of the HVAC Control Module.

Important: The module memory will not clear if the battery positive voltage circuit fuse is installed in less than 60 seconds.

Wait 60 seconds.

Install the fuse.

Wait 60 seconds before moving the HVAC controls.

(I'm not sure if the links below are still good)
The guy at dealership told me to remove the panel under steering wheel and i could get to actuators. They quoted me $150 to change it, that was part included.

The actuator has a feedback circuit to the control head. What happens is that the sweep resistor in the actuator might lose contact once in a while. When that happens, the control head doesn't know where the door is in the case and will default it all the way to one side.

the Driver's Side Temp Actuator seemed to have died. The driver's side would stay at full HOT no matter what I changed the Auto Temp Control to...

I finally ordered the actuator (PN 89018676) and tore the lower dash apart yesterday after work. As soon as I looked up under the dash, there was the "faulty" part...with the wiring harness plug sitting next to it, NOT plugged in! So I plugged it back in and tested everything...what do you know, it worked perfectly!
I recall unplugging it to make access to the Mode Door Actuator a lot easier. And I proceeded to forget to plug it back in!

There is the mode actuator which changes the vents which the HVAC system is set to blow air our of.
Then there is a temp actuator for each side (driver & passenger) that adjusts the temp of the air coming from the vents on the respective side of the truck.
You changed the driver side temp actuator. That is the easy one to change.
HVAC Mode Door Actuator?

Whenever the battery is disconnected the HVAC unit will perform a recalibration of all doors. This causes the door motors to be moved full cycle and the mode door will stick some times. I now hook a jump box to the system before changing the battery in Trailblazers or Envoys to prevent a recalibration from occurring.
Sparky's Answers - 2003 GMC Envoy, No A/C Vent Control, B0263
Sparky's Answers - 2004 Chevrolet Trailblazer, Identifying Heater A/C Actuators
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