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.
A/C Operation Description at ECM: Notes
ECM controls the A/C compressor relay and condenser cooling fan relay according to signals from HVAC control unit, A/C refrigerant pressure sensor, ECT sensor and evaporator temperature sensor. The A/C switch ON signal from HVAC control unit is transmitted to ECM through BCM by CAN communication system. For more information about CAN communication system, refer to CAN COMMUNICATION SYSTEM DESCRIPTION .
ECM turns ON the A/C compressor relay when the vehicle state satisfy conditions described below.
- A/C switch ON signal is input from HVAC control unit
- A/C refrigerant pressure is within specified range
- Evaporator temperature is within specified range
- Engine speed is within specified range
- Engine coolant temperature is lower than specified value
- Throttle opening is lower than specified value
- Vehicle is not in either state of starting or quick acceleration
- ECT sensor malfunction is not detected
- A/C refrigerant pressure sensor malfunction is not detected
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.