Heating and Air Conditioning: Description and Operation

With the ignition switch in ON, battery voltage through the WIPER fuse is applied to the coil of the A/C relay and to the A/C switch. With the A/C switch ON and the blower switch in any position except OFF, a ground signal is sent through the normally closed contacts of the A/C thermostat to the PCM A/C request input at terminal C248/6. Ground is also provided to the A/C ON indicator in the A/C switch.

Operating parameters permitting, the PCM will ground the coil of the A/C relay at PCM terminal C248/4. The A/C relay energizes and applies battery voltage through the closed contacts of the relay and the normally closed contacts of the A/C dual pressure switch to the A/C compressor clutch. The clutch engages and the vehicle interior begins to cool.