For 1990-2009 cars

### HVAC Control Components

#### HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The HVAC module assembly is operated manually by a combination of electrical and mechanical components. The case is of a 3-piece, plastic construction. The left and right cases are assembled with a centre divider that houses the doors and are secured together with screws. The case sump is secured to the upper case assembly with screws. The blower resistor is integrated into the HVAC control module which is screwed to the HVAC blower motor fan assembly, which in turn is secured to the HVAC unit with a combination of pivot pins and screws.

#### Cold Operation

When the temperature switch is turned to the Full Cold position, it locates the air mix door in a position that does not allow any air to flow through the heater core. The result is that all air entering the vehicle cabin will be external air temperature.

#### Warm Operation

When the temperature switch is turned from the Full Cold position, it pulls the air mix doors open. When the temperature switch is turned to a warm position, the air mix doors will be partially open. This will cause some incoming air to pass through the heater core and some air to bypass the heater core. The mixture of heated and cool air will result in warm air entering the vehicle cabin.

#### Hot Operation

When the temperature switch is turned to the Full Hot position, the air mix doors will be in a position that directs all incoming air through the heater core. Therefore, all air entering the vehicle cabin will be heated air.

#### Mode Actuators

The mode actuators are used to adjust the mode positions and temperature. The mode actuators consist of a DC drive motor, reduction gears, printed circuit board (PCB) and a photo electric cell. The DC motors are provided with a supply voltage of 12 Volts from the HCM. The photo interrupter counts the revolutions of the DC motor drive shaft, these counts are then used by the HCM for reference to the actuator position.

#### Recirculation Actuator

The recirculation actuator is used to adjust the fresh air inlet/recirculation door. The recirculation actuator consists of a DC drive motor, reduction gears, printed circuit board (PCB) and a photo electric cell. The DC motors are provided with a supply voltage of 12 Volts from the HCM. The photo interrupter counts the revolutions of the DC motor drive shaft, these counts are then used by the HCM for reference to the actuator position.