Function Selector Switch
WARNING: This page is about a different car, the 2006 Lincoln Navigator and 2006 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
The function selector switch combines a vacuum selector valve to determine air distribution, and an electrical switch to supply battery voltage to the A/C compressor circuit and blower motor circuit. When the function selector switch is in the MAX A/C, DEFROST or FLOOR/DEFROST positions, the A/C compressor will be operational regardless of the A/C request switch status.