Refrigerant Pressure Sensor / Switch: Description and Operation

A/C On Signal, Pressure Sensor And Clutch Control Relay:

The A/C pressure sensor is used to indicate high side pressure to the ECM for use in determining cooling fan, A/C compressor and idle speed control. A fault in the A/C pressure sensor circuit should set a code 66 and cause the ECM to disable the compressor clutch. The A/C pressure sensor also provides low and high side pressure protection for the system.

If the A/C pressure signal exceeds about 4.86 volts indicating a high side pressure of about 428 psi, the clutch is disabled. If the A/C pressure sensor voltage is below about 0.58 volts indicating a pressure about 43 psi the clutch is disabled also.