GM Service Manual Online
For 1990-2009 cars only

Auxiliary Heater

An optional auxiliary heater supplies heat to the vehicle. The unit operates independently of the standard heater. The control on the instrument panel regulates the unit. The system consists of a separate heater core and the blower fan.

The heater hoses extend from the unit to a vacuum operated water valve. The hoses connect to the standard heater hoses.

Blower Speed Control-Auxiliary

The 3-speed blower switch provides the following settings:

    • LO
    • MED
    • HIGH

The blower motor switch is located in the instrument panel, above the radio. The blower motor switch also triggers an electro-mechanical valve to control coolant flow to the auxiliary heater core.

In the LO speed position, the circuit continues through the heater wiring harness to 2 resistors in the blower motor resistor relay.

In the MED speed position, the circuit continues through the heater wiring harness to 1 resistor in the blower motor resistor relay.

In the HIGH speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, and closes the relay's normally open contact. This provides full power to the blower motor from the HVAC MaxiFuse®.