A/C high and low pressure switches may be used in the PCM-monitored A/C request circuit. Switches are normally closed, completing the circuit between ignition and PCM. PCM will engage or disengage A/C compressor clutch relay based upon status of this circuit. When system refrigerant pressure increases beyond a certain point, high side switch will open, causing A/C request circuit voltage to drop.
If system refrigerant level decreases, causing refrigerant pressure to drop below normal, low side pressure switch will open, causing A/C request circuit voltage to drop. Switches may be used as normal clutch cycling devices or as safety devices which prevent compressor damage in the event of excessively high or low refrigerant pressure.