Low Pressure Sensor / Switch: Description and Operation

Rear A/C Low Pressure Switch:

The rear A/C low pressure switch provides a signal to the rear A/C control module to regulate the rear refrigerant system pressure and control rear A/C evaporator temperature. The rear A/C control module will disengage the rear A/C clutch if the rear refrigerant system suction line pressure falls below 30 kPa (4.4 psi).

The rear A/C low pressure switch is mounted on a fitting located on the rear suction line near the left side of the rear A/C evaporator housing.

The rear refrigerant system must be discharge prior to removing the rear A/C low pressure switch.

The rear A/C low pressure switch is electrically connected in series with the rear A/C high pressure switch, between ground and the rear A/C control module.

The rear A/C low pressure switch contact opens or closes the path the ground, signaling the rear A/C control module to turn the rear A/C clutch on and off. This regulates the rear refrigerant system pressure and controls rear A/C evaporator temperature. Controlling the rear evaporator temperature prevents condensate water on the evaporator fins from freezing and obstructing rear A/C system air flow.

The rear A/C low pressure switch contacts are open when the rear suction line pressure is approximately 152 kPa (22 psi) or lower. The rear A/C low pressure switch contacts will close when the rear suction line pressure rises to approximately 234 to 262 kPa (34 to 38 psi) or above. Lower ambient temperatures, below approximately -1° C (30° F), will also cause the rear A/C low pressure switch contacts to open due to the pressure/temperature relationship of the refrigerant in the system.

The rear A/C low pressure switch is factory-calibrated and cannot be adjusted or repaired and, if faulty or damaged, it must be replaced. Refer to the appropriate wiring information for complete HVAC wiring diagrams.