Rear Window Defogger Operation

INTRODUCTION

Rear Window Defogger System:

An electrically heated rear window defogger is an available factory-installed option on models equipped with a single rear door option. The defogger will only operate when the ignition switch is in the On position. When the defogger switch is turned to the On position, an electric heater grid on the rear window glass is energized. This grid will produce heat to help clear the window glass of ice, snow, or fog.

The defogger system is controlled by a switch, relay, and timer module located in the heater-A/C control bezel, which is in the instrument panel inboard of the steering column. An amber indicator lamp in the switch bezel will light to indicate when the defogger system is turned on. The defogger system will be automatically turned off after a programmed time interval of about ten minutes.

The 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.

SYSTEM OPERATION
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 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.

Defogger Switch, Relay, And Timer Module
The rear window defogger switch, relay, and timer are integrated into a single module. The module is mounted in the heater-A/C control bezel on the instrument panel. The switch, relay, and timer circuit is protected by a fuse in the fuse block module.

Actuating the momentary switch energizes the relay and electronic timer circuit. This causes electrical current to flow through the rear window glass heating grid circuit for approximately ten minutes, or until the rear window defogger switch or ignition switch are turned to the Off position. An amber Light-Emitting Diode (LED) in the switch bezel illuminates to indicate when the defogger system is turned on.

The defogger switch, relay, and timer module cannot be repaired. If faulty or damaged, the entire module must be replaced.