Low Pressure Sensor / Switch: Description and Operation

The low pressure cut-off switch is located on the suction line jumper near the filter-drier in the engine compartment. The switch is screwed onto a fitting on the suction line jumper that contains a Schrader-type valve, which allows the switch to be serviced without discharging the refrigerant system. The suction line jumper fitting is equipped with an O-ring to seal the switch connection.

The low pressure cut-off switch is connected in series electrically between the fin sensing cycling clutch switch and the Powertrain Control Module (PCM). The switch contacts open and close causing the PCM to turn the compressor clutch ON and OFF. This helps to regulate the refrigerant system pressure and protects the compressor from damage due to loss of refrigerant and refrigerant oil.

The low pressure cut-off switch contacts are open when the suction pressure is about 48 to 90 kPa (7 to 13 psi) or lower. The switch contacts will close when the suction pressure rises to about 103 to 172 kPa (15 to 25 psi) or above. Lower ambient temperatures, below about -1 °C (30 °F), will also cause the switch contacts to open. This is due to the pressure/temperature relationship of the refrigerant in the system.

The low pressure cut-off switch is a factory-calibrated unit. It cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.