F 350 2WD Pickup V8-460 7.5L VIN G EFI (1997)
Refrigerant Pressure Sensor / Switch: Description and Operation
A/C Pressure Switch
The A/C cycling switch is mounted on a Schrader valve fitting on the side of the suction accumulator/drier assembly. A valve depressor, located inside
the threaded end of the A/C cycling switch, presses in on the Schrader valve stem as the A/C cycling switch is mounted and allows the suction pressure
inside the suction accumulator/drier housing to activate the A/C cycling switch. The electrical contacts will open when the suction pressure drops to
163-175 kPa (23.5-25.5 psi). They will close, activating the A/C clutch, when the suction pressure rises to 276-324 kPa (40-47 psi). Lower ambient
temperatures (below approximately 1°C (30°F) during cold weather seasons will also prevent A/C compressor operation, because of the
pressure/temperature relationship of the refrigerant in the system.
NOTE: Temperature must drop to -4°C (25°F) to open pressure switch contacts. Contacts open at approximately -4°C (25°F) decreasing and close
increasing 7.2-10°C (45-50°F).
The electrical contacts control the electrical circuit to the A/C clutch field coil. When the contacts are closed, the A/C clutch field coil is energized and
the A/C clutch is engaged to drive the A/C compressor. When the contacts are open, the A/C clutch field coil is de-energized, the A/C clutch is
disengaged and the A/C compressor does not operate. The A/C cycling switch, when functioning properly, will control the pressure at a point where the
plate-fin surface temperature of the A/C evaporator core will be maintained slightly above freezing, which prevents icing and the blockage of airflow.
