Air Delivery: Defog
WARNING: This page is about a different car, the 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
When the driver selects the MIX-BLEND mode, air delivery is divided between the floor and windshield outlets. The HVAC control module ground the mix-blend mode valve solenoid control circuit. When the solenoid is grounded, vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red and the Yellow vacuum lines. The mode actuator will retract, closing the vent door. Applying vacuum to both sides of the defroster actuator will hold the defroster door stationary in the half open position. The heater door will also be held stationary in the half open position through mechanical linkage.