System Controls: Mix
WARNING: This page is about a different car, the 1994 Ford Mustang. However, it is still accessible from the selected car via links, so may be relevant.
With function selector knob in MIX position, outside air is drawn into system and past evaporator core. The cable-operated temperature blend door setting determines amount of input air heated by heater core and allowed to by-pass heater core.
The heater air damper door receives partial vacuum. As a result, this door opens half-way to allow airflow to the floor, demisters and the defroster. The windshield defroster door, without vacuum applied, cuts off airflow to the dash panel.