Low Pressure Sensor / Switch: Testing and Inspection

A/C Low Pressure Switch Test
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 too loose it may not open the Schrader-type valve in the accumulator fitting, which will prevent the switch from correctly monitoring the refrigerant system pressure. Also verify that the refrigerant system has the correct refrigerant charge. (Refer to - DIAGNOSIS AND TESTING - A/C PERFORMANCE Heater Diagnosis)

Remember that 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. For circuit descriptions and diagrams.

1. Disconnect and isolate the battery negative cable.
2. Unplug the a/c low pressure switch wire harness connector from the switch on the accumulator fitting.
3. Install a jumper wire between the two cavities of the a/c low pressure switch wire harness connector.
4. Connect a manifold gauge set to the refrigerant system service ports..
5. Connect the battery negative cable.
6. Place the a/c heater mode control switch knob in any A/C position and start the engine.
7. Check for continuity between the two terminals of the low pressure cycling clutch switch. There should be continuity with a suction pressure reading of 296 kPa (43 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 switch sense circuit as required. If not OK, replace the faulty switch.