Heater Option Only (C42)
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
On non-A/C equipped vehicles, the air temperature is controlled by moving the temperature knob. Moving the air temperature knob mechanically moves the air temperature door. They are linked together by the air temperature cable. The air temperature door position determines the amount of air directed to flow across the heater core. The recirculation mode will only be available when the HVAC control modules is in Bi-Level mode only.