Low Pressure Sensor / Switch: Testing and Inspection

Before performing diagnosis of the A/C low pressure switch, be certain that the switch is properly installed on the accumulator fitting. If the 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.

1. Verify that the refrigerant system has the correct refrigerant charge .
2. With gear selector in park or neutral and park brake set, start engine and allow to idle.
3. Place the A/C-heater mode control switch in any A/C position.
4. Raise hood and disconnect the wire harness connector from the A/C low pressure switch.
5. Using a suitable jumper wire, install the wire between the two terminal cavities of the A/C low pressure switch wire harness connector. The A/C compressor clutch should engage.
6. If the A/C compressor clutch does not engage, the A/C compressor clutch, A/C compressor clutch relay, A/C-heater mode control switch, A/C high pressure switch, PCM, fuses or related wiring circuits may be defective.
7. If the A/C compressor clutch does engage, connect a manifold gauge set to the low side refrigerant system service port.
8. Check for continuity between the two terminals of the A/C low pressure switch. There should be continuity with a suction pressure reading of 276 kPa (40 psi) or above, and no continuity with a suction pressure reading of 172 kPa (25 psi) or below. If OK, test and repair the A/C compressor clutch, A/C compressor clutch relay, A/C-heater mode control switch, A/C high pressure switch, PCM, fuses or related wiring circuits as required. If not OK, replace the faulty A/C low pressure switch.