Function Control Knob
WARNING: This page is about a different car, the 1995 Ford Pickup, 1995 Ford F-Super Duty, 1995 Ford Cab & Chassis, and 1995 Ford Bronco. However, it is still accessible from the selected car via links, so may be relevant.
The function control knob actuates a vacuum selector valve, which directs vacuum to open and close vacuum motor-controlled doors. With knob in NORM A/C, VENT, FLOOR, MIX or DEF (defrost symbol) position, outside air is drawn into system by the blower. With knob in OFF or MAX A/C position, the outside/recirculation door is positioned so outside air cannot pass into evaporator case. See Figure.