B4000 SE Regular Cab 4WD V6-4.0L OHV (1999)
Air Conditioning Switch: Description and Operation
The A/C cycling switch is mounted on a Schrader valve- type fitting on the top of the receiver/drier.
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A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem.
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This allows the suction pressure inside the receiver/drier to control the operation of the A/C cycling switch.
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The electrical switch contacts open when the suction pressure drops to 152 - 193 kPa (22 - 28 psi).
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The contacts close when the suction pressure rises to 276 - 324 kPa (40 - 47 psi).
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When the A/C cycling switch contacts close, the signal to energize the A/C clutch is sent to the A/C clutch relay.
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When the A/C cycling switch contacts open, the A/C clutch field coil is deenergized and compressor operation stops.
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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.
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This prevents icing of the evaporator core and blockage of airflow.
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It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.