Compressor HVAC: Description and Operation

How the Circuit Works

A/C Compressor Controls
Voltage is provided at all times to the heater control panel through fuse 25 and to the A/C compressor clutch relay contacts through fuse 58. With the ignition switch ON (II) and the engine not cranking, voltage is supplied to the control panel and the relay coil through fuse 20. The control panel is grounded at G402.

When you push the A/C button ON with the ignition switch ON (II) and the heater fan switch not in the OFF position, the control panel will ground the A/C ON request from input of the ECM through the A/C pressure switch. The ECM then grounds the A/C compressor clutch relay coil. This energizes the coil, which closes the relay contacts and provides voltage through fuse 58 to the A/C compressor clutch. The clutch then engages and begins turning the compressor.