Compressor HVAC: Description and Operation

How the HVAC Circuit Works

Compressor Controls

Voltage is provided at all times to the heater control panel through fuse 13 (in the passenger's under-dash fuse/relay box), and to the A/C compressor clutch relay contacts through fuse 58. With the ignition switch ON (II), voltage is supplied to the control panel and the relay coil through fuse 3 (in the driver's under-dash fuse/relay box). The control panel is grounded at G401.

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 input of the PCM or ECM through the A/C pressure switch. The PCM or 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.

How the Climate Control Circuit Works

The climate control unit controls the blower controls, air delivery, and A/C compressor controls either automatically or semi-automatically. The control unit receives battery voltage at all times through fuse 13 (in the passenger's under-dash fuse/relay box). With the ignition switch in ON (II), battery voltage is supplied through fuse 3 (in the driver's under-dash fuse/relay box). The control unit is grounded at G401.

A/C Compressor Controls

Voltage is provided at all times to the A/C compressor clutch relay contacts through fuse 58. With the ignition switch ON (II), voltage is supplied to the relay coil through fuse 3 (in the driver's under-dash fuse/relay box).

With the ignition switch ON (II), the climate control unit grounds the A/C ON input of the PCM through the A/C pressure switch. The PCM 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. By default, when the climate control system is on, the A/C is on.