RAM 1500 Truck 2WD V6-3.9L VIN X (1999)
High Pressure Sensor / Switch: Description and Operation
SYSTEM OPERATION
High Pressure Cut-off Switch
The high pressure cut-off switch is located on the discharge line near the compressor. The switch is screwed onto a fitting that contains a
Schrader-type valve, which allows the switch to be serviced without discharging the refrigerant system. The discharge line fitting is equipped with
an O-ring to seal the switch connection.
The high pressure cut-off switch is connected in series electrically with the low pressure cycling clutch switch between ground and the Powertrain
Control Module (PCM). The switch contacts open and close causing the PCM to turn the compressor clutch on and off. This prevents compressor
operation when the discharge line pressure approaches high levels.
The high pressure cut-off switch contacts are open when the discharge line pressure rises above about 3100 to 3375 kPa (450 to 490 psi). The
switch contacts will close when the discharge line pressure drops to about 1860 to 2275 kPa (270 to 330 psi). When checking refrigerant system
pressures with a manifold gauge set, keep in mind that the indicated pressures will be about 172 kPa (25 psi) below the actual switch pressure
values due to the pressure drop that occurs in the refrigerant system between the switch and the high pressure service port.
The high pressure cut-off switch is a factory-calibrated unit. The switch cannot be adjusted or repaired and, if faulty or damaged, it must be
replaced.
