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 would start with trying a system recalibration. There is a link on the left side bar of this site. If the actuator type problems persist please read the information at the following post address. It pertains to the hot cold complaints.
http://www.sparkys-answers.com/2010/12/2002-chevrolet-trailblazer-no-heat.html
The mode actuator for your 2002 is different from the rest but the actuator is in the same general location.
The front blower issue is likely going to be a faulty blower resistor and harness connector but read the information at the following repair post address. There is plenty of test information for you to find your problem.
http://www.sparkys-answers.com/2010/02/2006-chevrolet-trailblazer-blower-inop.html
After you check all of your fuses, I would recommend inspection of the rear blower motor. I have not done a post on this yet but I have done one on a related subject that will show you how to get to the rear blower motor and resistor.
http://www.sparkys-answers.com/2012/01/2003-chevrolet-trailblazer-clicking.html
Having same problems as some in the post just not sure what steps to take and order.
02 Trailblazer LS
#1. Driver’s Side blows heat only, Passenger Side is cold only.
#2. Air/Heat Contols don’t change air flow placement. It always blows out of the dash vents and defrost vents.
#3. Fan speed 5 turns off system. Other speeds work.
#4. No rear air even with knob in back seat.
Sorry, lots of info but any help would be appreciated.
If you are referring to the engine rpm’s dropping at idle when the a/c is turned on and this has happened after a battery disconnect. The problem will be carbon build up on the throttle plate.
Could this cause the motor to drag when the a/c button is turned on?
You will need to pull the HVAC B fuse in the rear fuse box, under the rear seat. It may also be listed as fuse #36 and should be a 10 amp fuse.