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 Pressure Switches
A/C high and low pressure switches may be used in the PCM-monitored A/C request signal circuit. Switches are normally closed, completing the circuit between ignition and PCM. PCM will engage or disengage A/C clutch relay based upon status of this circuit. When system refrigerant pressure increases beyond a certain point, high side switch will open, causing A/C request line voltage to drop. If system refrigerant level decreases, causing refrigerant pressure to drop below normal, low side pressure switch will open, once again causing A/C request line voltage to drop. Switches may be used as normal clutch cycling devices or as safety devices which prevent compressor damage in the event of excessively high or low refrigerant pressure.
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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.