Low Pressure Sensor / Switch: Description and Operation

A/C LOW PRESSURE SWITCH
The A/C low pressure switch is a single pole, single throw, pressure actuated switch that is installed in a threaded port into the suction passage of the accumulator. The switch is located on the top of the accumulator in a fitting that contains a Schrader type valve, which allows the switch to be serviced without discharging the refrigerant system. The accumulator fitting is equipped with a O-ring to seal the switch plumbing connection.

The A/C low pressure switch is a factory calibrated unit. The switch cannot be adjusted or repaired and if faulty or damaged it must be replaced.

The A/C low pressure switch monitors the pressure of the refrigerant leaving the accumulator to the compressor. The switch is connected in series electrically with the heater-A/C control blower and mode switches and the high pressure cut out switch between ground and the Powertrain Control Module (PCM). The switch contact open or close the path the ground, signaling the PCM to turn the compressor clutch on and off. This regulates the refrigerant system pressure and controls evaporator temperature. Controlling the evaporator temperature prevents con-densate water on the evaporator fins from freezing and obstructing air conditioning system air flow.

The A/C low pressure switch contacts are open when the suction pressure is approximately 152 kPa (22 psi) or lower. The switch contacts will close when the suction pressure rises to approximately 234 - 262 kPa (34 - 38 psi) or above. Lower temperatures, below approximately -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.