Rear Climate Control

The rear climate control system has the following features:

• The rear climate control system is functional whenever the front HVAC control module is in any mode.
• The rear blower motor recirculates the air inside the vehicle, outside air is not  available to the rear system.
• Air is cooled and dehumidified by the rear A/C evaporator core only if the front (main) climate control system is operating in a mode that requires A/C compressor operation.
• The rear air distribution doors are controlled by electric actuator motors.
• The rear climate control system has 2 rotary switches; one switch controls the blower motor speed and the other switch controls both temperature and airflow. Both rotary switches are located on the rear of the front floor console. Temperature and airflow are controlled together using the same rotary switch. When the temperature is set to full warm, the airflow discharges from the registers located in the rear of the B-pillar trim panels in front of the 2nd row seats. When the temperature is set to full cool, the airflow continues to discharge from the registers located in the rear of the B-pillar trim panels in front of the 2nd row seats and from the panel registers at the beltline in front of the 3rd row seats. A temperature setting between cold and hot results in a mixed airflow from all rear registers.
• The rear climate control system uses an electric booster heater to warm the air inside the vehicle (no heater core). For more information on the electric booster heater, Refer to: Supplemental Climate Control - System Operation and Component Description .

The Refrigerant Cycle 

For information on the refrigerant cycle, Refer to: Climate Control System - Vehicles With: Dual Automatic Temperature Control (DATC) - System Operation and Component Description . Refer to: Climate Control System - Vehicles With: Electronic Manual Temperature Control (EMTC) - System Operation and Component Description .

Control System Logic 

The rear blower motor control must be set to any speed other than 0 for the system to operate.

Controls and Compressor Operation 

All customer commands for the rear climate control system come through the RHVAC control module.

A/C Compressor Operation 

For information on the A/C Compressor and Clutch Operation, Refer to: Climate Control System - Vehicles With: Dual Automatic Temperature Control (DATC) - System Operation and Component Description . Refer to: Climate Control System - Vehicles With: Electronic Manual Temperature Control (EMTC) - System Operation and Component Description .

Rear A/C Request 

When the rear temperature-airflow control is set to full cold, the RHVAC control module activates the rear Thermostatic Expansion Valve (TXV) over a hardwired circuit only if the front A/C system is in operation and the rear evaporator discharge air temperature is above approximately 1°C (33.8°F).

The rear evaporator discharge air temperature sensor is a hardwired input to the RHVAC control module. The rear evaporator temperature sensor prevents icing of the rear evaporator core by measuring the temperature of the rear evaporator core. An accurate rear evaporator temperature is critical for rear Thermostatic Expansion Valve (TXV) activation. If the temperature of the rear evaporator is low enough to cause the condensed water vapor to freeze, the rear Thermostatic Expansion Valve (TXV) is deactivated by the RHVAC control module.

Air Handling 

When the rear blower motor is set to a speed other than 0, airflow is directed through both the rear evaporator core and the rear electric booster heater. Based on the temperature-airflow control settings, the rear air distribution door actuators direct airflow to the registers. The air source is from recirculated passenger compartment air, outside air is not available to the rear climate control system.

The rear LH and RH air distribution 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 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 calibrates itself so it knows how many steps there are for the actuator's full range of movement.

When a temperature-airflow mode is selected, the RHVAC control module drives the actuator motors in the direction necessary to make the actuator positions agree with the expected RHVAC control module position to be obtained.

The RHVAC control module sends a PWM signal to the rear blower motor control module to control the blower speed. The blower motor control module provides 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 blower motor control to a speed of 0 turns off the rear climate control system. When the rear blower motor control is set to a speed of 0:

• the rear electric booster heater is turned off.
• the rear Thermostatic Expansion Valve (TXV) is closed.
• the rear air distribution doors remain in the last commanded position.
• the rear blower motor is off.

PANEL 

When the rear blower motor control is set to a speed other than 0 and the temperature-airflow control is set to PANEL (or full cold):

• the rear electric booster heater is turned off.
• the rear Thermostatic Expansion Valve (TXV) is opened.
• the rear air distribution doors operate in combination to direct airflow to the registers located in the beltline in front of the 3rd row seats.
• the blower motor is on and the speed is adjustable.

PANEL-FLOOR 

When the rear blower motor control is set to a speed other than 0 and the temperature-airflow control is set to a point between PANEL and FLOOR (or full cold and full hot):

• the rear electric booster heater is turned on (the output stage depends on the temperature-airflow control setting, the hotter the setting, the more output stages are activated).
• the rear Thermostatic Expansion Valve (TXV) is activated (how much the valve is opened depends on the temperature-airflow control setting, the colder the setting, the more the valve is opened).
• the rear air distribution doors operate in combination to direct airflow to the registers located in the rear of the B-pillar trim panels in front of the 2nd row seats and the registers at the beltline in front of the 3rd row seats (depending on the temperature-airflow setting, colder setting results in more airflow to the beltline in front of the 3rd row seats registers, hotter setting results in more airflow to the registers located in the rear of the B-pillar trim panels in front of the 2nd row seats).
• the rear blower motor is on and the speed is adjustable

FLOOR 

When the rear blower motor control is set to a speed other than 0 and the temperature-airflow control is set to FLOOR (or full hot):

• the rear electric booster heater is turned on.
• the rear Thermostatic Expansion Valve (TXV) is closed.
• the rear air distribution doors operate in combination to direct airflow to the registers located in the rear of the B-pillar trim panels in front of the 2nd row seats.
• the blower motor is on and the speed is adjustable.