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.
Circuit Description
When air conditioning and blower fan are selected, and system has a sufficient refrigerant charge, a 12-volt signal is supplied to the A/C request input of the PCM. A/C request signal may be temporarily canceled during system operation by the electronic thermostat in the evaporator case. When A/C request signal is received by PCM, PCM supplies a ground from A/C compressor clutch relay if engine operating conditions are within acceptable ranges. With A/C compressor relay energized, voltage is supplied to the compressor clutch coil. PCM will enable the compressor clutch to engage whenever A/C has been selected with engine running, unless any of the following conditions are present:
- Throttle is open 90% or more.
- Ignition voltage is less than 10.5 volts.
- Engine speed is more than 4500 RPM for 5 seconds.
- Engine coolant temperature 257°F (125 °C) or more.
- Intake air temperature is less than 41°F (5°C).
- Power steering pressure switch signals a high pressure condition.
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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.