Refrigerant Pressure Sensor / Switch: Description and Operation

A/C Cycling Switch
The A/C cycling switch is mounted on a Schrader valve-type fitting on the top of the suction accumulator/drier.
^ A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem.
^ This allows the suction pressure inside the suction accumulator/drier to control the operation of the A/C cycling switch.
^ The electrical switch contacts open when the suction pressure drops. The contacts close when the suction pressure rises.
^ When the A/C cycling switch contacts close, the A/C compressor clutch field coil is energized.
^ When the A/C cycling switch contacts open, the A/C compressor clutch field coil is de-energized and A/C compressor operation stops.
^ The A/C cycling switch will control the evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing.
^ This prevents icing of the evaporator core and blockage of airflow.
^ It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.

Pressure Cutoff Switch
The pressure cutoff switch is used to interrupt A/C compressor operation in the event of high system discharge pressures.
^ The pressure cutoff switch is mounted on a Schrader valve-type fitting on the high pressure side.
^ A valve depressor, located inside the threaded end of the pressure cutoff switch, presses on the Schrader valve stem.
^ This allows the pressure cutoff switch to monitor the compressor discharge pressure.
^ When the A/C compressor discharge pressure rises, the switch contacts open, disengaging the A/C compressor. When the pressure drops, the contacts close to allow operation of the A/C compressor.
^ It is not necessary to discharge the refrigerant system to remove the pressure cutoff switch.