Heated Glass Element: Description and Operation

Rear Window Defogger System Schematic:

ATC Control Head:

REAR WINDOW DEFOGGER
The Rear Window Defogger electrical system involves the operation of the Heater- A/C or ATC Control Head, the Body Control Module (BCM), and the rear Window Defogger Relay and wiring. The system consists of a rear glass with two vertical bus bars and a series of electrically connected grid lines fired on the inside surface. The Body Control Module (BCM) operates a relay located in the trunk area on all models.

Vehicles with Rear Window Antenna refer to Audio Systems.

Vehicles equipped with an electrically heated rear window defogger also have a 90 amp generator.

The passenger can push the Rear Widow Defogger button on the Heater- A/C or ATC Control to defog the rear glass. The system will only operate when the ignition switch is in the run position. Once the Rear Widow Defogger button is pushed, the button indicator will light and the system will operate for a period of time and then automatically turn off. Refer to the owner's manual for operation of the A/C-Heater or ATC control.

When the rear window defogger relay is ON, current is directed to the rear defogger grid lines. The heated grid lines heat the rear glass to clear the surface of fog or frost.

Circuit protection is provided by a fusible link, located in the charging circuit, for the heated grid circuit and by a fuse for the relay control circuit.

The A/C-Heater or the ATC control sends a signal to the BCM, which indicates to the BCM that the operator wants the rear window grid to heat. Refer to the A/C-Heater or ATC Control for details on how these modules interact. An output wire from the BCM connects to the coil of the rear window defogger relay. The other side of the coil is connected to a fuse. The BCM turns on the relay by connecting the output line of the BCM to vehicle ground. The relay contacts will then close supplying vehicle power to the rear window defogger grid.

CAUTION: Grid lines can be damaged or scraped oft with sharp instruments, care should be taken in cleaning glass or removing foreign materials, decals or stickers. Normal glass cleaning solvents or hot water used with rags or toweling is recommended.