Battery voltage is applied to the defogger relay, through the DEF fuse, which is HOT at all times and is permanently grounded at G400.

When the rear defogger switch is depressed, connector cavity A1 of the rear window defogger relay is energized through CKT 267 (ORN), a ground is provided to the switch from G201. This also activates a timer within the HVAC controller. Because the rear defogger is a resistive element, the defogger begins to heat when voltage is applied. Since the indicator is grounded to G201, the indicator lights when voltage is applied.

The HVAC controller incorporates an integral timer circuit. The timer circuit will terminate the rear defogger operation after approximately 10 minutes or when the ignition switch is moved out of the RUN position.