A/C High Pressure Switch

The high refrigerant pressure switch is located in the compressor discharge line. The switch performs the following functions:
^ Monitors the compressor discharge pressure.
^ Acts as a safeguard in order to prevent refrigerant blow-off from the compressor pressure relief valve.
^ Disengages the compressor in the case of refrigerant pressure above 2965 kPa (430 psi). In this function the switch supplements the A/C high side temperature sensor.

Pressure readings above 2465 kPa (430 psi) open the switch, cutting off the power supply to the relay, and disengage the compressor clutch. Pressures will begin to drop. When the pressure drops to 1379 kPa (200 psi), the switch closes and allows the compressor to engage. Compressor cycling, which is caused by the pressure switch, is considered normal. This can occur under the following conditions:
^ High temperature
^ High humidity
^ Extended idle
^ Slow vehicle speed
^ Tail wind

If cycling occurs as the result of other conditions, a blocked line or condenser is possible. Perform the appropriate service.