Refrigerant Pressure Sensor / Switch: Description and Operation

DESCRIPTION AND OPERATION
The clutch cycling pressure switch will control the evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing which prevents evaporator icing and the blockage of air flow.

A valve depressor, located inside the threaded end of the pressure switch, presses in on the schrader valve stem as the switch is mounted and allows the suction pressure inside the accumulator/drier housing to control switch operation. The electrical switch contacts are normally open when the suction pressure is at or below 168 kPa (24.5 psi); they will close when the suction pressure rises to approximately 324 kPa (47 psi) or above. Lower ambient temperatures (below 10° C or 50° F), during winter cold weather seasons, will also open the clutch cycling pressure switch contacts due to the pressure/temperature relationship of the refrigerant in the system. The electrical switch contacts control the electrical circuit to the compressors magnetic clutch coil. When the switch contacts are closed, the clutch coil is energized and the A/C clutch is engaged to drive the compressor. When the switch contacts are open, the compressors magnet clutch coil is de-energized, the A/C clutch is disengaged and the compressor does not operate.