GM Service Manual Online
For 1990-2009 cars only

After disconnecting the battery or experiencing a complete power loss, synchronize the electronically operated actuators as follows:

  1. Turn ignition to the RUN position.
  2. Simultaneously press the AUTO and OFF buttons (located on the heat and A/C control head) for at least five seconds.
  3. After initiation, the stepper motors will cycle from one stop to the other. You may hear the motors cycling while calibrating.