Dakota 4WD V6-3.9L VIN X (1997)
High Pressure Sensor / Switch: Description and Operation
Fig 25 High Pressure Cut-off Switch -- Typical
HIGH PRESSURE CUT-OFF SWITCH
The high pressure cut-off switch is located on the discharge line near the compressor. This switch is connected in series between the low pressure
clutch cycling switch and the Powertrain Control Module (PCM). This switch prevents compressor operation when the discharge line pressure
approaches high levels.
When the discharge line pressure rises above 3100 to 3375 kPa (450 to 490 psi) the switch contacts open and interrupt the A/C request signal
circuit to the PCM. The PCM responds by de-energizing the compressor clutch relay, which will cause the compressor clutch to disengage. The
switch will close again when the pressure drops to 1860 to 2275 kPa (270 to 330 psi).
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.
Fig 29 Low Pressure Cycling Clutch Switch Removal/Installation
LOW PRESSURE CYCLING CLUTCH SWITCH
The low pressure cycling clutch switch is mounted on top of the accumulator. The switch is connected in series with the high pressure cut-off
switch in the A/C request signal circuit, between the heater-A/C mode control switch and the Powertrain Control Module (PCM).
The switch contacts open and close causing the PCM to turn the compressor clutch on and off. This regulates the system pressure and controls
evaporator temperature. Controlling evaporator temperature prevents condensate water on the evaporator fins from freezing and obstructing air
conditioning system air flow.
The switch contacts are normally open when the suction pressure is approximately 172 kPa (25 psi) or lower. The switch will close when the
suction pressure rises to approximately 296 kPa (43 psi) or above.
Lower ambient temperatures, below approximately -1~C (30~F) during cold weather, will also open the switch contacts. This is due to the
pressure/temperature relationship of the refrigerant in the system.
