Heated Glass Element: Description and Operation

Rear Window Defogger System
The rear window defogger system consists of a tinted glass that has a number of horizontal ceramic enamel compound element lines and two vertical bus bars baked onto the inside surface during the glass forming operation. The feed terminal is soldered to the bus bar on the driver side or passenger side. The ground terminal is soldered to the passenger side or driver side. The system is used to melt ice or snow from the exterior surface of the rear window or to clear up condensation from the interior surface of the rear window.

Under some conditions, heat from the glass may not be detected by touch. The length of time required to remove interior fog from the back glass are functions of temperature, atmospheric pressure and number of passengers.

This system uses a pod (area above radio) mounted switch with an integral ON indicator lamp. The ON/OFF function of this system is manual. The off function of the system is also controlled by a timer in the chime module or by cycling the ignition switch.

The system only operates with the ignition in the Run position.

The rear defog switch is a momentary switch and when pressed On, the switch provides a ground input to the chime module to start the timer and keep this circuit grounded for the appropriate time. The chime module also provides a ground path for current through an LED ON indicator lamp in the switch assembly. When the relay coil is energized, current flows through the rear defogger element to ground.

A variable power density grid pattern is used on the rear defogger grid. The power density in the center section is greater than the power density to either side of the center section. This design results in uniform clearing of the entire grid area.

Circuit Timing Description
The chime module provides the timing function and ground for the RR defog relay and On indicator. When the rear defog switch is pressed for the first time in an ignition cycle, the rear defog element and switch indicator will go On and stay On for 12 minutes unless the ignition is turned to either the ACC, START or LOG position or the rear defog switch is pressed again. Subsequent activation's of the switch, prior to cycling the ignition, when the rear defog is Off will result in the same operation, except the time the defogger is On is reduced to 7.5 minute.