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 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 3100 to 3375 kPa (450 to 490 psi). The switch contacts will close when the discharge line 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 35 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, 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 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 low pressure cycling clutch switch contacts are open when the suction pressure is approximately 141 kPa (20.5 psi) or lower. The switch contacts will close when the suction pressure rises to approximately 234 to 262 kPa (34 to 38 psi) or above. Lower ambient temperatures, below approximately -10C (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.

The low pressure cycling clutch switch is a factory- calibrated unit. It cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.



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.

The low pressure cycling clutch switch is a factory-calibrated unit. This switch cannot be adjusted or repaired. If faulty or damaged, the switch must be replaced.