Heated Glass Element: Description and Operation

WINDOW DEFOGGER
Rear Window Defogger
The rear window defogger system will only operate when the ignition switch is in the run position. When the defogger switch is in the run position, an electric heater grid on the rear window glass is energized. Vehicles with the heated mirror options also have heater grids located behind the outside rear view mirror glass. Each of these grids produce heat to help clear the rear window glass and outside rear view mirrors of ice, snow, or fog.

The rear window defogger system is controlled by a switch installed with the HVAC control assembly An amber indicator lamp in the switch button will light to indicate when the rear window defogger system is turned ON. The instrument cluster circuitry, which contains the defogger system timer logic, monitors the state of the defogger switch through a hard-wired input. The instrument cluster circuitry controls the rear window defogger system through a hard-wired control output to the rear window defogger relay The rear window defogger timer and logic circuitry cannot be adjusted or repaired and, if faulty or damaged, the instrument cluster assembly must be replaced.

The rear window defogger system will be automatically turned OFF after a programmed time interval of about ten minutes. After the initial time interval has expired, if the rear window defogger switch is turned ON again during the same ignition cycle, the defogger system will automatically turn OFF after about five minutes.

The rear window defogger system will automatically shut OFF if the ignition switch is turned to the OFF position, or it can be turned OFF manually by depressing the instrument panel switch. Following are general descriptions of the major components in the rear window defogger system. Refer to the owner's manual in the vehicle glove box for more information on the features, use and operation of the defogger system.

REAR WINDOW DEFOGGER GRID
The heated rear window glass has two electrically conductive vertical bus bars and a series of horizontal grid lines made of a silver-ceramic material, which is baked on and bonded to the inside surface of the glass. The grid lines and bus bars comprise a parallel electrical circuit.

When the rear window defogger switch is placed in the ON position, electrical current is directed to the rear window grid lines through the bus bars. The grid lines heat the rear window to clear the surface of fog or snow. Protection for the heated grid circuit is provided by a fuse in the Power Distribution Center (PDC).

The grid lines and bus bars are highly resistant to abrasion. However, it is possible for an open circuit to occur in an individual grid line, resulting in no current flow through the line.

The grid lines can be damaged or scraped OFF with sharp instruments. Care should be taken when cleaning the glass or removing foreign materials, decals, or stickers from the glass. Normal glass cleaning solvents or hot water used with rags or toweling is recommended.

A repair kit is available to repair the grid lines and bus bars, or to reinstall the heated glass pigtail wires.