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 A/C low pressure switch is electrically connected in series with the A/C high pressure switch, between ground and the powertrain control module (PCM). The A/C low pressure switch contact opens or closes the path the ground, signaling the PCM to turn the A/C compressor clutch on and off. This regulates the refrigerant system pressure and controls evaporator coil temperature. Controlling the evaporator temperature prevents condensate 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 141 kPa (20.5 psi) or lower. The switch contacts will close when the suction 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 switch contacts to open. This is due to the pressure/temperature relationship of the refrigerant in the system.