Probably the mode door actuator. We have instructions on the replacement procedure on our enthusiasts forum at www.trailvoy.com
It's called the mode door actuator and it is up in the vent system.
The part cost 139.99 from the local auto store.
The mode door actuator on a 2003 Chevrolet Trailblazer is located behind the dashboard, specifically on the passenger side. You will need to remove the lower dash panel and possibly the glove compartment to access it. The actuator is typically mounted on the HVAC housing. Be sure to disconnect the battery before attempting any repairs to avoid electrical issues.
This is a failure of the mode door actuator in the venting system. We have instructions in our enthusiasts forum on how to change it out. www.trailvoy.com
The mode door actuator has failed. We have instructions for repair at www.trailvoy.com
Could be the mode door actuator. For more info visit our enthusiasts forum at www.trailvoy.com
new mode actuators must be reprogrammed with scan tool that is capable of reflash.
It controls which vent the air comes out of.
It controls which vent the air comes out of.
Only one thing there. The blower motor for the heating and AC. Turn it off and see if it still happens. A constant faint clicking sound may indicate a failing mode door actuator. If the blower does not seem like the issue and change in frequency of clicks with the speed setting then the mode door actuator and an inability to select air flow may be your problem. www.trailvoy.com
Try this from AutoZone.com http://www.autozone.com/addVehicleId,2934501/initialAction,repairGuide/shopping/repairGuide.htm?pageId=0900c152801c9c89