With the ignition switch in the RUN position, voltage is applied through the HVAC CTL fuse (CKT 41) and the DIC/HVAC fuse (CKT 541) to the Heater-A/C Control. The voltage from CKT 733 (LT BLU)is varied from the battery to approximately 1.5 V by the temperature control potentiometer. The control assembly provides a ground path through CKT 150 (BLK).

Control of air through the system is regulated by vacuum. At various points on the control, mode valves mix and direct cooled, heated and outside air through the air ducts. Refer to Vacuum System