Air Handling

Airflow is directed through the rear evaporator core and the rear heater core based on the rear fan speed control and the temperature and air distribution control settings. The air source is from recirculated passenger compartment air, outside air is not available to the rear climate control system.

The rear temperature door actuator is a stepper motor. There is no feedback circuit or potentiometer for this actuator. 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. The RHVAC 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 RHVAC control module tracks the actuator positions by counting steps and periodically calibrating itself so it knows how many steps there are for the actuator's full range of movement.

When the temperature and air distribution control is selected, the RHVAC control module sends a signal to direct the actuator motor in the direction necessary to agree with the selected rotary switch position.

To control the speed of both rear blower motors, the RHVAC control module sends a PWM signal to the correct rear blower motor speed control. The blower motor speed control provides a variable ground feed for the blower motor. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

OFF 

Setting the rear fan speed control rotary switch to 0 turns off the rear climate control system. When the rear blower motor control is set to 0:

• the rear temperature door remains in the last commanded position.
• the rear blower motors are off.

PANEL 

When the rear fan speed control rotary switch is set to a speed other than 0 and the temperature and air distribution control rotary switch is set to PANEL (or full cold):

• the rear heater temperature door is closed.
• the rear heater blower motor is off.
• the rear A/C blower motor is on and the speed is adjustable.

PANEL-FLOOR 

When the rear fan speed control rotary switch is set to a speed other than 0 and the temperature and air distribution control rotary switch is set to a point between PANEL and FLOOR (or full cold and full hot):

• the rear temperature door is directed to the selected rotary switch position.
• the rear heater blower motor is on and the speed is adjustable.
• the rear A/C blower motor is on and the speed is adjustable.

FLOOR 

When the rear fan speed control rotary switch is set to a speed other than 0 and the temperature and air distribution control rotary switch is set to FLOOR (or full hot):

• the temperature door is open 100%.
• the air flow is routed to the floor vent.
• the rear heater blower motor is on and the speed is adjustable.
• the rear A/C blower motor is off.