Module, HVAC: Operation

The Heating, Ventilation, and Air Conditioning (HVAC) Module (also known as the A/C heater module) utilizes integrated circuitry and information carried over the Controller Area Network (CAN) data bus to monitor many sensors and switch inputs throughout the vehicle. In response to those inputs, the internal circuitry and programming of the HVAC module allows it to control electronic functions and features of the heating and A/C system.

Some of the inputs received by the HVAC module over the CAN bus are as follows:

• A/C Request
• Ambient Air Temperature
• Electric Backlight (EBL) Request
• Electrical System Voltage
• Engine Coolant Temperature
• Engine Speed
• Humidity, Windshield Glass Temperature and Dewpoint (ATC only)
• Refrigerant Pressure
• Vehicle Identification Number
• Vehicle Odometer

Some of the messages broadcasted by the HVAC module on the CAN bus are as follows:

• A/C Clutch Engage
• Auto Headlight Signal
• EBL Status

The HVAC module receives the following information over hardwired circuits:

• Auto Headlight Signal
• Evaporator Temperature
• Interior Air Temperature
• Left and Right Sun Load

The HVAC module monitors and controls the following over hardwired circuits:

• Driver and Passenger Blend Door Positions
• Blower Motor Speed
• Mode Door Position
• Recirculation Door Position

The HVAC module is diagnosed using a scan tool. Prior to replacing an HVAC module, run the calibration procedure to verify that the concern is not an air door calibration issue. Refer to STANDARD PROCEDURE .

The HVAC cannot be adjusted or repaired and must be replaced if inoperative or damaged.