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. 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.

Also verify that the refrigerant system has the correct refrigerant charge.
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 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 switch sense circuit as required. If not OK, replace the faulty switch.