High Pressure Sensor / Switch: Description and Operation

High Pressure Cutoff Switch

The high pressure cut-off switch is used to interrupt A/C compressor operation in the event of high system discharge pressures.
- The high pressure cut-off switch is mounted on a Schrader valve-type fitting on the high pressure side of the condenser to evaporator line.
- A valve depressor, located inside the threaded end of the high pressure cut-off switch, is used to monitor the compressor discharge pressure.
- It is not necessary to discharge the refrigerant system to remove the A/C pressure cut-off switch.
- The high pressure cut-off switch has two sets of contacts. One electrical contact is normally closed.
- When the compressor discharge pressure rises to approximately 3,103 kPa (450 psi), the switch contacts open, disengaging the A/C compressor.
- When the pressure drops to approximately 1,724 kPa (250 psi), the contacts close to allow operation of the A/C compressor.

The switch contains a second set of electrical contacts used for high-speed fan control.
- When the compressor discharge pressure reaches approximately 2,241 kPa (325 psi), these contacts close and engage the high-speed fan control.
- When the pressure drops to approximately 1,896 kPa (275 psi), the contacts again open and the high speed fan control is disengaged.