GM Service Manual Online
For 1990-2009 cars only

The heater system provides heating, forced air and power ventilation, side window defogging, and windshield defrosting. Outside air is drawn from the plenum at the base of the windshield into the heater module by the blower fan. Additional outside air, called ram air, is forced into the heater module by the forward movement of the vehicle.

Within the heater module, the air is heated as required and then routed through ducts to the proper outlets for discharge into the passenger compartment. A control assembly in the instrument panel allows the operator to control blower speed, mode of operation and temperature of the air coming from the heater system.

The heater module contains components that heat the air flowing through the module and directs the air to the proper ducts and outlets. The heater module consists of two assemblies: the heater assembly and the blower assembly. The heater assembly mounts to the rear surface of the cowl panel beneath the instrument panel. The blower assembly mounts to the front surface of the cowl panel in the engine compartment.

Hot coolant from the engine's cooling system is directed through the heater core and returned to the cooling system while the engine is running. The heater core transfers heat from the coolant to the air passing through the core fins.