A/C Pressure Switch

The A/C cycling switch is mounted on a Schrader-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 to 151-165 kPa (22.0-24.0 psi). The contacts close when the suction pressure rises to 276-324 kPa (40-47 psi). This is due to the pressure/temperature relationship of the refrigerant and the requirement of the system pressure to reach 276-324 kPa (40-47 psi) to close the A/C cycling pressure switch contacts.

These contacts control the electrical circuit to the A/C clutch field coil. When the A/C cycling switch contacts close, voltage is supplied to energize the A/C clutch for operation of the A/C compressor. When the A/C cycling switch contacts open, the A/C clutch is de-energized and operation of the A/C compressor stops.

The A/C compressor 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 airflow.