Heated Glass Element: Description and Operation

REAR WINDOW DEFOGGER SYSTEM CONTROL
The rear window defogger switch, rear window defogger indicator lamp, rear window defogger mirror electronic timer/control/logic circuitry and rear window defogger relay are all integral to the heater and air conditioner control assembly, which is located below the radio in the instrument cluster bezel on the instrument panel. The momentary-type switch provides a hard wired battery signal to the electronic circuitry each time it is depressed. An amber rear window defogger indicator lamp above the rear window defogger switch lights to indicate when the rear window defogger system is turned On.

The rear window defogger electronic timer/control/ logic circuitry responds to the switch input by energizing or de-energizing the rear window defogger relay. Energizing the rear window defogger relay provides electrical current to the rear glass heating grid.
The rear window defogger switch, rear window defogger indicator lamp, rear window defogger electronic timer/control/logic circuitry and rear window defogger relay cannot be repaired. If damaged or faulty, the entire heater and air conditioner control assembly must be replaced.

REAR GLASS HEATING 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 heating 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 terminals.