GM Service Manual Online
For 1990-2009 cars only

The heater system provides the following functions:

    • Heating
    • Ram air
    • Power ventilation
    • Windshield defrosting

The blower fan draws outside air into the heater module from the plenum at the base of the windshield. Additional outside air, called ram air, is forced into the heater module by the forward movement of the vehicle. The heater module heats the air as required. Ducts then carry the air to the proper outlets for discharge into the passenger compartment. The operator controls the blower motor speed, the mode of operation, and the temperature of the incoming air through an HVAC control assembly in the instrument panel.

The heater module contains components that heat the air flowing through the heater module and direct the air to the proper ducts and outlets. These components are enclosed inside a two-part housing. The front housing mounts to the front of the cowl panel in the engine compartment. The rear housing mounts to the rear of the cowl panel in the passenger compartment under the instrument panel.