A/C Compressor Controls

When the Ignition Switch is in RUN, battery voltage is applied through Fuse 20 to the A/C Select Switch on the A/C Control Panel. When the A/C Select Switch is pressed voltage is applied to terminal 3 of the Evaporator Temperature Regulator. The Evaporator Temperature Regulator applies voltage from terminal 2 to the coil in the A/C Compressor Control Unit through the Refrigerant Pressure Switch, allowing current to flow from Fuse 19 to the Compressor.

The Refrigerant Pressure Switch will disengage the Compressor Clutch when refrigerant pressure rises above 30.0 bar (435 psi) or when a lose of refrigerant brings the pressure below 1.5 bar (21.8 psi). The Evaporator Temperature Regulator will detect the Refrigerant Pressure Switch opening at terminal 5 and will turn off the output voltage at the compressor control terminal. The Evaporator Temperature Regulator will not allow the compressor clutch to be turned on again until the circuit continuity has been restored between terminals 5 and 2. The Evaporator Temperature Regulator tests for continuity by momentarily applying voltage at the Compressor Control every 8 to 10 seconds. Voltage at the A/C Clutch Monitor Input indicates continuity. The Evaporator Temperature Regulator will continue to apply voltage at the Compressor Clutch output, which will allow the compressor clutch to be energized. The Evaporator Temperature Sensor signals the Evaporator Temperature Regulator to deenergize the Compressor Clutch when evaporator temperature is low enough that freezing may result.

Clutch Diode
Whenever the Compressor Clutch is de-energized, the collapsing magnetic field induces a voltage in the winding. The Clutch Diode provides a path for the resulting current.