GM Service Manual Online
For 1990-2009 cars only

The HVAC system delivers air that has been heated or cooled and dehumidified for occupant comfort. The HVAC system also provides the following features:

    • Ventilation
    • Windshield defrosting
    • Side window defogging

During most operating condition, the blower motor draws the outside air through the heater and air conditioning module. The forward movement of the vehicle forces additional air into the vehicle. The following actions occur in the evaporator core when the compressor is on:

    • The air is filtered
    • The air is dehumidified
    • The air is cooled to about 2°C (35°F)

Some of the air then passes through the heater core where the flow of hot coolant reheats the air. Depending on the temperature door position, the heated air is mixed with cold air from the evaporator before the air enters into the passenger compartment. The air enters the passenger compartment through the upper, lower, or defroster outlets. This provides positive air flow even if the windows are closed.

When the Recirc mode is selected, most of the air entering the evaporator and heater core module is recirculated from the passenger compartment. Recirculated air is most likely cooler and dryer than outside air in very hot weather.