Air Handling

All airflow from the blower motor passes through the evaporator core. Based on the climate control system temperature settings, the temperature door actuator directs airflow through or around the heater core as needed. The air distribution door actuator controls the airflow to the defrost, footwell or panel register vents. The air source is from either fresh air or recirculated passenger compartment air as determined by the air inlet door actuator position. The air inlet door actuator contains a reversible electric motor with no potentiometer and is either fully open or fully closed.

The air distribution door and temperature door actuators are stepper motors. There is no feedback circuit or potentiometer for these actuators. The pins labeled Door A, B, C and D are for the different phases (coils) of the motor. All the phases for a given motor are fed from a common power lead, the pin labeled Door Power and the HVAC control module controls each phase by turning a low side output on or off for the different phases. The motor turns, or steps, through a series of motions to position the actuator. The HVAC control module tracks the actuator positions by counting steps and periodically calibrates itself so it knows how many steps there are for the actuator's full range of movement.

The blower motor has 4 speeds controlled by the HVAC control module and a blower motor resistor.

Off 

When the system is off:

• the air inlet door closes.
• the blower motor is off.

Max A/C 

When MAX A/C mode is selected:

• the air inlet door closes allowing only recirculated air.
• the recirculated air indicator is illuminated (recirculated air forced on).
• the A/C button is illuminated.
• the A/C compressor operates if the outside air temperature is above approximately 0 °C (32 °F).

Panel 

When PANEL mode is selected:

• the mode doors direct airflow to the instrument panel registers.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature is only cooled below the outside air temperature when the A/C is commanded on.

Panel-Floor 

When PANEL-FLOOR mode is selected:

• the mode doors direct airflow to the floor duct and the instrument panel registers. A small amount of airflow from the side window demisters and defrost duct is present.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature is only cooled below the outside air temperature when the A/C is commanded on.

Floor 

When FLOOR mode is selected:

• the mode doors direct airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature is only cooled below the outside air temperature when the A/C is commanded on.

Floor-Defrost 

When FLOOR-DEFROST mode is selected:

• the mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature is only cooled below the outside air temperature when the A/C is commanded on.

Defrost 

When DEFROST mode is selected:

• the mode doors direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
• the recirculated air request button can not be enabled.
• the A/C is automatically commanded on and remains on until the system is either turned off or the airflow mode has changed and the A/C button is pressed.