Refrigerant Pressure Sensor / Switch: Description and Operation

Voltage is provided at all times to the heater control panel through fuse 13, and to the A/C compressor clutch relay contacts through fuse 59. With the ignition switch ON (II), voltage is supplied to the control unit and the relay coil through fuse 3. The control panel is grounded at G401.

When you push the A/C button ON with the ignition switch ON (II) and the heater fan switch not in the OFF position, the control panel will ground the A/C ON input of the PCM through the A/C pressure switch. The PCM then grounds the coil in the A/C compressor clutch relay. This energizes the coil, which closes the relay contacts and provides voltage through fuse 59 to the compressor clutch. The clutch then engages and begins turning the compressor.

The A/C pressure switch is located in the condenser outlet line where refrigerant is in a high temperature, high pressure liquid state. The switch will sense abnormally high or low pressure, and open the circuit. This removes the ground signal from the PCM, and turns off the compressor.