Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Description And Operation
DESCRIPTION
The Heating, Ventilation, and Air Conditioning (HVAC) module (1) is a microcontroller designed to operate the heating and A/C system, using the Controller Area Network (CAN) - IHS data bus. The HVAC module has a plastic housing with two electrical connector receptacles, one mounting screw hole and two locating tabs. The 36-pin wire harness connector contains the circuits for the controls on the HVAC housing and the A/C heater control. The 8-pin wire harness connector contains the power circuits and CAN-IHS circuits that connect the HVAC module to the other modules in the vehicle.
The HVAC module is mounted to the left side of the HVAC housing, above the accelerator pedal.
OPERATION
The HVAC module utilizes integrated circuitry and information carried over the CAN-IHS 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-IHS bus are as follows:
- A/C Request
- Ambient Air Temperature
- Electric Back Light (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 broadcast by the HVAC module on the CAN-IHS bus are as follows:
- A/C Clutch Engage
- Auto Headlamp Signal
- EBL Status
The HVAC module receives the following information over hard wired circuits:
- Auto Headlamp Signal
- Evaporator Temperature
- Interior Air Temperature
- Left and Right Sun Load
The HVAC module monitors and controls the following over hard wired 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 module cannot be adjusted or repaired and must be replaced if inoperative or damaged.
Refer to the Heating and Air Conditioning Description and Operation for additional information. Refer to DESCRIPTION AND OPERATION .
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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