GM Service Manual Online
For 1990-2009 cars only

Rear Window Defogger System Components

The rear window defogger system consists of the following components:

    • HVAC control assembly
    • Rear window defogger grid

Rear Window Defogger Operation

Battery positive voltage is supplied through the HTD MIR/RR-DEFOG fuse in the underhood fuse block to the HVAC control assembly. Ignition voltage is supplied through the HTR--A/C fuse in the IP fuse block to the HVAC control assembly. Ground for the HVAC control assembly is provided by G200. The circuits mentioned for the HVAC control assembly are primarily for the rear window defogger system. When the ignition is ON, and the rear window defogger switch is depressed, the HVAC control assembly illuminates the rear window defogger indicator and allows battery positive voltage through the RR DEFOG fuse in the IP fuse block to the rear window defogger grid. Ground for the rear window defogger grid is provided by G403.

When the rear window defogger switch is depressed for the first time, the defogger cycle lasts for 10 minutes. Further operation will result in 5 minute defogger cycles.