GM Service Manual Online
For 1990-2009 cars only

A vacuum regulates the control of air through the system. Various positions on the control cause the mode valves to mix and direct cooled, heated and outside air through the air ducts.

Air flows through the HVAC system as described for each of the following modes:

    • OFF
        A light bleed of air flows from all of the outlets.
    • MAX
        Recirculated air flows through the instrument panel outlets.
    • NORM, A/C
        Outside air flows through the instrument panel outlets.

Object Number: 82066  Size: SH
    • BI-LEVEL
        Outside air flows through the following outlets:
       - The instrument panel outlets
       - The floor outlets

Object Number: 82067  Size: SH
    • VENT
        Outside air flows through the instrument panel outlets.
        The compressor does not operate.

Object Number: 82065  Size: SH
    • HEATER
        Most of the air flows through the floor outlets. A small amount of air flows through the defroster duct.

Object Number: 82070  Size: SH
    • DEFOG
        Equal amounts of air flow through the floor outlets and the defrost outlets.

Object Number: 82071  Size: SH
    • DEFROST
        Most of the air flows through the defroster outlets. A small amount of air flows through the floor outlets.

The operation of the cooling fan is controlled by the PCM through the cooling fan relay.

Ducts and Outlets

A system of ducts and outlets direct air to the passenger compartment.

Obstructions in the ducts and outlets may cause poor air output. Inspect the following air passages for obstruction, such as leaves or dirt:

    • The defroster duct
    • The heater duct
    • The A/C ducts
    • The vent ducts

A/C systems also come equipped with side window defoggers.