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.
- 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 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 signal to energize the A/C clutch is sent to the wide open throttle A/C cutoff relay.
- When the A/C cycling switch contacts open, the A/C clutch field coil is de-energized and compressor operation stops.
- The A/C cycling switch will control the A/C evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing.
- This prevents icing of the A/C evaporator core and blockage of air flow.
- It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.







Pressure Cutoff Switch - Dual Function
The pressure cutoff switch - dual function is used to interrupt A/C compressor operation in the event of high system discharge pressures.
- The pressure cutoff switch - dual function is mounted on a Schrader valve-type fitting on the high pressure side of the A/C manifold and tube.
- It is not necessary to discharge the refrigerant system to remove the pressure cutoff switch - dual function.
- A valve depressor, located inside the threaded end of the pressure cutoff switch - dual function, presses on the Schrader valve stem.
- This allows the pressure cutoff switch - dual function to monitor the compressor discharge pressure.
- When the 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.

The pressure cutoff switch - dual function has a second set of electrical contacts used for high-speed cooling fan control.
- When the compressor discharge pressure rises, the contacts close and engage the high speed fan control. When the pressure drops, the contacts open and the high speed fan control is disengaged.