For 1990-2009 cars

### System Description

The rear window defogger system consists of the following components:

• | RR DEFOG fuse

• | RR DEFOG relay

• | Rear window defogger grid

• | HVAC control module

Battery positive voltage is supplied through the RR DEFOG fuse in the underhood fuse block to the REAR DEFOG relay switched input. Ground for the RR DEFOG relay is provided by G102. Ground for the rear window defogger grid is provided by G304.

When the rear window defogger switch is pressed, the HVAC control module provides voltage to the RR DEFOG relay coil, energizing the relay. When the relay is energized, the relay switch closes allowing B+ voltage to flow through the closed relay switch to the rear window defogger grid. The properties of the rear window defogger grid has a resistance to the flow of electrical current causing the elements within the grid to radiate heat.

When the rear window defog switch is pressed, the HVAC control module keeps the RR DEFOG relay control circuit for active for 15 minutes, additional activation of the rear window defogger system results in 7.5 minute activation cycles except when the vehicle speed is greater than 80 km/h (50 mph) which results in a continuous rear window defogger operation.