Auxiliary Climate Control Assembly

AUXILIARY CLIMATE CONTROL ASSEMBLY





The auxiliary climate control assembly is a reheat unit, which cools the air to a constant value then reheats it as necessary to produce the required temperature. The assembly is installed on the left side of the loadspace, behind the rear quarter panel. A grille in the rear quarter panel allows air to flow from the loadspace into the auxiliary climate control assembly.

The auxiliary climate control assembly consists of a casing, formed from a series of plastic molding, which contains:
^ A blower
^ A blower control module
^ An evaporator
^ A heater core
^ A temperature blend door
^ A distribution door
^ An evaporator temperature sensor.

Refrigerant and coolant lines from the engine compartment are connected to pipes from the evaporator and the heater core immediately below the loadspace floor. Where the pipes, and the evaporator drain tube, pass through the loadspace floor, the aperture is sealed by a seal plate.

Internal passages, integrated into the casing of the auxiliary climate control assembly, guide the air from the blower through the evaporator and heater core to the distribution outlets.

The temperature blend door regulates the flow of air through the heater core to control the temperature of the air leaving the auxiliary climate control assembly. A stepper motor installed on the rear of the casing operates the temperature blend door.

The distribution door regulates the flow of air through the face level outlet and the foot level outlet. A stepper motor installed on the top of the casing operates the distribution door.

The temperature blend stepper motor and the distribution stepper motor are both connected to a Local Interconnect (LIN) bus, which also connects the ACCM with the ATCM. Each stepper motor incorporates a microprocessor which operates the motor in response to LIN bus messages from the ACCM. The stepper motors are powered by a feed from the ATCM, and share a ground connection with the rear blower control module.

The ACCM determines the positions of the distribution and temperature blend doors by using either their closed or open position as a datum and memorizing the steps that it drives the individual stepper motors. Each time the ACCM is activated by the ATCM, it checks the memorized position of the stepper motors against fixed values for the current distribution and temperature settings on the control panel. If there is an error, the ACCM calibrates the applicable stepper motor, to re-establish the datums, by driving them fully closed or open before re-setting them to their nominal selected position. A calibration run can also be invoked using T4.

Air Flow Through Auxiliary Climate Control Assembly





The blower is in the air inlet of the auxiliary climate control assembly, and consists of an open hub, centrifugal fan powered by an electric motor. Operation of the blower is controlled by the ACCM, using the rear blower relay in the Battery Junction Box (BJB) and the blower control module. The blower control module is installed in the auxiliary climate control assembly downstream of the blower, where any heat generated during operation is dissipated by the air flow. A wiring harness on the auxiliary climate control assembly connects the blend door motor, distribution door motor, blower and blower control module to the vehicle wiring.

Blower Control Module





When the blower is required, the ACCM energizes the coil of the rear blower relay. The energized rear blower relay supplies battery power to the blower motor, which is connected to ground through the blower control module. The speed of the blower is controlled by the blower control module, which regulates the blower motor voltage in response to a Pulse Width Modulated (PWM) signal from the ACCM. To vary the blower motor voltage the ACCM varies the duty cycle of the PWM signal.

Evaporator Temperature Sensor





The evaporator temperature sensor is a Negative Temperature Coefficient (NTC) thermistor installed in the auxiliary climate control assembly on the downstream side of the evaporator. The evaporator temperature sensor supplies a temperature signal to the ACCM.