412-03D Auxiliary Climate Control: Description And Operation (page 4 of 14)

 
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

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Temperature blend door motor

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Face level outlet