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.
Hey Sparky, I have an 03 Chevy 2500HD with the 6.0L. I have the full Auto dual climate control, and it is now blowing completly cold air, even when on 90 degrees F. and it is also not changing any of the vents, it is stuck on defrost and floor. I have tried the recalibration multiple times, all with no success other than it continuing to blow cold air from the defrost and floor vents. My Heater core is not blocked, because both of my coolant lines going in and out are both the normal hot. After multiple “suspicions” of what might be wrong, all of which turned out to be ok, other than these actuators you are talking about. Now since my temperature is not changing and the vents are not changing, do i need both the temp. actuator and mode actuator? Thanks, Joe.
Hi
I have a 2003 Envoy XL. The front a/c and heat work great, but in the summer the rear vents blow hot air and in the winter they blow cold air. Any ideas?
Thanks
The information at the following post link should help.
http://www.sparkys-answers.com/2011/08/2005-gmc-sierra-air-blows-only-from.html
Sparky,
I tried to do the recalibaration on my 2003 GMC Sierra 1500 and now the speed controls work but the ac will only blow out of the front vents and not the floor and defroster. Any ideas or what part i might need.
Nick
Replacing the thermostat will most likely take care of the code P0128. It will not help with the others. I would recommend replacing the thermostat and having the codes cleared. Then drive the vehicle and see which codes come back first. Do you happen to know how well the throttle plate was cleaned? A stall or near stall condition caused by a dirty throttle plate can induce MAP sensor codes on these vehicles.