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.
HVAC Control System Description
Following data are sent from each control module to the HVAC control module through CAN communication. For CAN communication system, refer to description on COMMUNICATION SYSTEM DESCRIPTION .
- Engine coolant temperature
- Engine speed
- A/C refrigerant pressure
- Vehicle speed (wheel speed)
- Outside air temperature
- Evaporator temperature
- A/C compressor clutch state
Based on above data, HVAC control module sends A/C compressor ON/OFF request signal to ECM through CAN communication.
Furthermore, when the defrost switch is turned on or the "MODE" (air flow) switch is selected to "D/F" mode, HVAC control module sends A/C compressor ON request signal to BCM through CAN communication to clear fog from windshield.
BCM sends this signal through CAN communication to ECM which then causes A/C compressor relay to turn ON/OFF.
For more information on signal transmission and reception of Auto A/C system, refer to HVAC ELECTRONIC CONTROL INPUT/OUTPUT BLOCK DIAGRAM .
NO RELATED
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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.