Compressor HVAC: Description and Operation

How the Circuit Works

A/C Compressor Controls

Voltage is provided at all times to the A/C compressor clutch relay contacts through fuse 1 (in under-hood fuse/relay box). With the ignition switch ON (II), voltage is supplied to the relay coil through fuse 14 (in under-dash fuse/relay box).

With the ignition switch ON (II), the heater control panel grounds the A/C ON input of the ECM through the A/C pressure switch and the multiplex control unit. 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 1 (in under-dash fuse/relay box) to the A/C compressor clutch. The clutch then engages and begins turning the compressor.

The A/C button at the recir-A/C-rear defogger switch assembly must be pressed to activate the A/C system.