Compressor HVAC: Description and Operation

When the ignition switch is in the RUN position it connects circuit A1 from fuse 4 in the Power Distribution Center (PDC) to circuit A22. Circuit A22 supplies battery voltage to fuse 12 in the fuse block. Fuse 12 powers circuit C1.

Circuit C1 supplies battery voltage to the A/C blower switch. Circuit C21 connects the A/C blower switch to the A/C low pressure switch.

When the operator selects A/C operation, the A/C blower switch provides the A/C request signal to cavity 27 of the Powertrain Control Module (PCM) on circuit C91. At the same time, the blower switch supplies voltage through the A/C thermostat to circuit C21.

Circuit C21 supplies voltage to the A/C low pressure switch. When the A/C low pressure switch closes, circuit C20 provides battery voltage to the contact side of the A/C compressor clutch relay and provides the A/C select signal to the PCM. Circuit C20 is double crimped at the contact side of the relay. The C20 circuit branch from the relay supplies the A/C select input to cavity 28 of the PCM.

After receiving the A/C request signal, the PCM energizes the A/C compressor clutch relay by providing ground for the coil side of the relay on circuit C13. Circuit C13 connects to cavity 34 of the PCM.

Circuit G5 from fuse 9 in the fuse block supplies voltage to the coil side of the relay. In the START or RUN positions the ignition switch connects circuit A1 from fuse 4 in the PDC with circuit A21. Circuit A21 connects to the fuse block bus bar that powers circuit C5 through fuse 9.

When the PCM energizes the A/C compressor clutch relay, the relay switches from its normally grounded position to connect circuit C20 to circuit C3. Circuit C3 supplies voltage to the case grounded A/C compressor clutch.