Low Pressure Sensor / Switch: Testing and Inspection

NOTE: Lower ambient temperatures, below about -1° C (30° F), during cold weather will open the A/C low pressure switch contacts and prevent A/C compressor operation due to the pressure/temperature relationship of the refrigerant.

Before performing diagnosis of the A/C low pressure switch, verify that the refrigerant system has the correct refrigerant charge and that the A/C low pressure switch is properly installed on the accumulator fitting. If the A/C low pressure switch is not properly installed, it may not open the Schrader-type valve in the accumulator fitting, which will prevent the switch from correctly monitoring the refrigerant system pressure.

The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.
1. With gear selector in Park or Neutral and with park brake set, start the engine and allow it to idle.
2. Place the A/C-heater mode control in any A/C position.
3. Disconnect the wire harness connector from the A/C low pressure switch.
4. Using a suitable jumper wire, install the jumper wire between the two terminals of the wire harness connector for the A/C low pressure switch. The A/C compressor clutch should engage. If the A/C clutch does engage, replace the faulty A/C low pressure switch. If the A/C clutch does not engage, the A/C clutch, A/C clutch relay, A/C-heater control, A/C high pressure switch, PCM or ECM (depending on engine application), fuses or related wiring circuits may be defective. Repair as required.