Automatic Operation

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In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation.

To place the HVAC system in Automatic mode, the following is required:

The Auto switch must be activated
The air temperature switch must be in any other position other than full hot or full cold position

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature:

Monitor the following sensors:

Inside Air Temperature Sensor
Ambient Air Temperature Sensor
Lower Left Air Temperature Sensor
Lower Right Air Temperature Sensor
Upper Left Air Temperature Sensor
Upper Right Air Temperature Sensor
Regulate blower motor speed.
Position the air temperature actuator.
Position the mode actuator.
Position the recirculation actuator.
Request A/C operation.

In automatic operation, the auxiliary HVAC control module will maintain the comfort level inside of the vehicle by controlling the auxiliary blower motor, the auxiliary air temperature actuator and the auxiliary mode actuator.

To place the auxiliary HVAC system in Automatic mode, the following is required:

The auxiliary blower motor switch on the auxiliary HVAC control assembly must be in the Auto position.
The auxiliary mode switch on the auxiliary HVAC control assembly must be in the Auto position.
The auxiliary air temperature switch must be in any other position other than full hot or full cold position.

Once the desired temperature is reached, the auxiliary blower motor, auxiliary mode and auxiliary temperature actuator will automatically be adjusted to maintain the temperature selected. The auxiliary HVAC control module performs the following functions to maintain the desired air temperature:

Upper Air Temperature Sensor - Auxiliary
Lower Air Temperature Sensor - Auxiliary
Regulate auxiliary blower motor speed
Position the auxiliary air temperature actuator
Position the auxiliary mode actuator

Engine Coolant

Engine coolant is the essential element of the heating system. The thermostat controls the normal engine operating coolant temperature. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation. Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC module. The ambient air drawn through the HVAC module absorbs the heat of the coolant flowing through the heater core. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. Opening or closing the air temperature door controls the amount of heat delivered to the passenger compartment. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.