GM Repair Problems? Ask GM Repair Expert Now.
Your problem most likely is a faulty air temperature actuator,but first make sure both heater hoses going into the front of the vehicle are hot (if not,possible restricted heater core).Here is some info to help you.
Temperature Valve Actuator Replacement Removal Procedure
Tighten Tighten the screws to 1.6 N·m (14 lb in).
The HVAC control module will relearn the actuator limits whenever power is disconnected and re-connected to the module.
Use the following steps to perform the calibration update:
Important: The scan tool must be disconnected from the vehicle to properly perform the calibration procedure. If a scan tool is connected before this procedure is completed, then new calibration values will not be stored.
Important: Failure to wait 60 seconds will not allow the HVAC control module sufficient time to clear the old calibration values.