The HVAC control module controls the REAR DEFOG relay located in the right rear fuse block. The rear window defog switch located on the HVAC control module is hard wired to the REAR DEFOG relay coil side. The rear window defog switch provides the request signal to the HVAC control module. When the rear window defog switch is pressed, the switch contacts close and ground is supplied. The HVAC control module interprets the flow of voltage as a request to activate the rear window defogger. The HVAC control module energizes the rear window defog relay by applying voltage to the relay coil via the rear defog relay control circuit. Ground for the relay coil is provided at G401. When the rear window defog relay coil is energized, the switch contacts of the rear window defog relay close allowing battery voltage to flow from the REAR DEFOG fuse through the closed switch contacts and out the relay switched output circuit to the rear window defogger grid. Ground for the rear window defogger grid is provided at G402. The HVAC control module also illuminates the rear defog indicator LED located on the HVAC control panel.

When you start the engine and activate the rear window defogger switch, the defogger cycle lasts for 15 minutes. Further operation will result in 7.5 minute defogger cycles. The rear window defogger cycle resets to 15 minutes when the ignition is cycled from OFF to ON.

The rear window defogger will not time out if vehicle speed is above 50 mph (80 km/h).