Fist thing to do that usually works is perform a reset and calibration of the mode doors and control head.
Chevy trailblazer blend door actuator reset.
Opening and closing the door can make a difference as the vehicle controls see this as cycle completion.
For manual systems it does not matter where the a c controls are set but if you feel the need to do something turn the blower switch on i prefer speed 3 and set the temperature.
The topic of how to perform the actuator recalibration procedure on chevrolet gmc and cadillac trucks and suvs has become an ever increasing topic of discussion.
This grind or click sound is actually the plastic gears stripping inside.
I have a 2002 chevrolet trailblazer ext.
Disconnect the wiring harness from the mode door actuator the mode door actuator has a white gear extending from one side and is the lower of the two actuators.
Now lay on you back with you head in the drivers floor board.
An actuator can go bad in of two ways.
A blend door actuator is made up of an electric motor that turns a plastic gear set in one direction or another which is connected to an air control door pivot at the final drive of the unit.
Look up see 2 screws remove them and the panel they hold on.
Re install fuses start truck and do not touch a c control head for 2 minutes.
This actuator assembly might fit a few other models but double check the part numbers for your car.
Pull the actuator from the hvac case.
Remove the screws from the actuator.
I just replaced the blend door mode actuator which did fix the problem the direction the vents blow but the driver side vents are still blowing warm air.
Parts counter people call this the upper actuator.
You may indeed need to replace an actuator.
Next start the vehicle and drive it a short distance and see how it performs.
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Look to left main wire harness needs to be moved to the right up and behind it is th blend actuator 7 32 socket to remove it then manually turn the white peg total labor 30 min.
Blend door ok first put you front seat down and back raise steering wheel.
On the gmc acadia and the chevrolet traverse the replacement part number for the blend door actuator is 15 73989.