HVAC Systems - Manual

HVAC CONTROL MODULE




The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the above features.

AUXILIARY HVAC CONTROL PROCESSOR
The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. It receives inputs from the front and rear auxiliary HVAC control assemblies. The processor positions the auxiliary air temperature actuator and auxiliary mode actuator based on these inputs. This processor does not have Class 2 communication available.

The auxiliary HVAC control processor receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through rear auxiliary HVAC control assembly and a splice pack. The system receives 12 volt varied voltage input for auxiliary air temperature change request. Then the processor creates a 12 volt varied output for control of the auxiliary air temperature actuator. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

FRONT AUXILIARY HVAC CONTROL ASSEMBLY
The front auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the Aux.position is selected, inputs from this control assembly will not be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The front auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when Aux.is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

REAR AUXILIARY HVAC CONTROL ASSEMBLY
The rear auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the rear headliner so that second row seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode and air temperature settings. When the Aux. position is selected, on the front HVAC control assembly, inputs from this control assembly will be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The rear auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when Aux.is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.