Low Pressure Sensor / Switch: Description and Operation

Fig.20 Low Pressure Clutch Cycling Switch:

The low pressure clutch cycling 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 an O-ring to seal the switch plumbing connection.

The low pressure clutch cycling switch is a factory calibrated unit. The switch cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The low pressure clutch cycling 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 contacts open or close the path to 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 condensate water on the evaporator fins from freezing and obstructing air conditioning system air flow.

The low pressure switch contacts are open when the suction pressure is approximately 1m152 kPa (22 psi)0m or lower. The switch contacts will close when the suction pressure rises to approximately 1m234 to 262 kPa (34 to 38 psi)0m or above. Lower ambient temperatures, below approximately 1m-1 1|C (30 1|F)0m, will also cause the switch contacts to open. This is due to the pressure/temperature relationship of the refrigerant in the system.