2003 GMC Sierra 1500 Q&A
2003 GMC Sierra 1500 Question: How to fix the air delivery problem?
Sounds like a damper door or the motor to control it is not working. you will have to look under the dashboard along the heater box and locate the motor to see if it is moving the arm door or not. Then go from there check voltage is getting to the motor if it isn't moving. If it is getting voltage but not working replace the motor, if it is working and the arm is moving but the door has no change you will need to replace the damper door. - torque wrench