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 Switch & Evaporator Switch
When A/C switch is in ON position and A/C low pressure switch and evaporator switch are closed, an A/C select signal is sent to PCM. If A/C low pressure switch or evaporator switch opens, the PCM will not receive an A/C select signal.
When A/C function is selected (A/C switch on), the A/C request signal provides information to the PCM from the A/C temperature control thermostat (evaporator switch). This signal indicates evaporator temperature is in the proper range for A/C operation.
The A/C request signal is used by PCM to determine required Idle Air Control (IAC) motor position, and to activate or deactivate A/C compressor clutch. When PCM receives an A/C request signal, it repositions the IAC motor to increase idle speed. The increased idle speed compensates for additional engine load caused by engagement of A/C compressor.
On Cherokee 4.0L equipped with A/C, whenever A/C compressor clutch is energized, PCM will energize auxiliary radiator (cooling) fan relay. This occurs regardless of engine coolant temperature.
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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.