A/C Low Pressure Switch Test

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

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 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 262 kPa (38 psi) or above, and no continuity with a suction pressure reading of 141 kPa (20.5 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 (diesel engine applications), A/C pressure transducer (gasoline engine applications), PCM, fuses or related wiring circuits as required. If not OK, replace the faulty A/C low pressure switch.