Air Handling

There are 3 door actuators that control the air flow into the passenger compartment:

• Air distribution
• Air inlet
• Temperature

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 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 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.