This 2003 GMC Envoy came in with the complaint that the a/c will only blow out the defrost and floor. Not through the dash vents. I checked codes and found a code B0263 for a fault with the mode actuator. I first ran into this problem after changing a battery in one of these vehicles last year. 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. This way I will not be blamed for a stuck actuator motor.
Anyways to change the actuator motor, first drop the hush panel under the driver’s side of the dash. There are some parts that have to be disconnected from the panel including the turn signal flasher assembly shown in the next picture.
Next, I removed the lower dash knee panel to have a little more room to work.
I had to pull a push pin retainer out at the left side of the duct work in order to remove the driver’s floor vent.
Now, I could finally see the actuator on the side of the heater a/c box.
I removed the actuator and installed the new one. Performed a recalibration with my Tech 2 and put all the panels back in place. A recalibration can be done by disconnecting the battery for at least one minute, reconnect the battery, start the engine and leave the a/c controls alone. I would recommend letting the engine run for at least two minutes, turn the ignition off for at least ten seconds but no more than thirty seconds and then restart the engine so that confirmation of the repair can be done.
I do not recommend connecting the wiring to the actuator until it is installed. They come prepositioned for easier installation.
The notch at the lower edge of the gear is an alignment point. There is a corresponding tab on the door linkage that needs to be lined up with this notch.
To purchase the mode valve actuator, please click here. To see updated information about actuator positions and alignment, please click here.
I recommend installing the harness connector after the actuator is mounted.
Thanks Sparky! You saved me $$$s. There was some confusion on my part as to whether I should connect the actuator before or after the recalibration. I took the gamble and connected it afterwards. It works like a dream in this 100+F weather. 🙂
Check all fuses in both the underhood and under rear seat fuse boxes. If all fuses are okay perform a recalibration procedure. There is a link on the left side bar.
I have a 2002 Trailblazer extended. My husband changed the battery and now I have no fan controll or digital read out. All vents are working just unfortunately blowing hot air. I have no control of reducing the fans. Unfortunately it is not comfortable since it is 90 out. Would this be the same problem as mentioned before? I have already paid $75 to a shop to tell me they don’t know what is wrong.
Sparky, just finished this repair this morning on my 2006 Trailblazer. Once you get familiar with the location of the parts and the feel of things up there, it wasn’t too bad. I’m not a car guy at all but couldn’t see paying a dealer for this. Took me a couple hours and well worth it. Keep up the excellent work. Very, very much appreciated.