Heated Glass Element: Description and Operation

HEATED GLASS SYSTEM
The rear window defogger system is used to defog and deice the rear window in cases of freeze up and humid conditions. The rear window defogger switch is located within the mode select knob on the HVAC control module on this model.

The Rear Window Defogger electrical system involves the operation of the Manual Temperature Control (MTC) 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 right side trunk area on all models.

Vehicles with Rear Window Antenna refer to Audio Systems.

The system consists of a rear glass with two vertical bus bars and a series of electrically connected grid lines on the inside surface. The control switch is located in the HVAC Control Module. The relay is located in the junction block. The timer is located in the Body Control Module (BCM).

Circuit protection for heated grid is provided by:
- A 40 amp EBL fuse located in the power distribution center
- Rear window defogger relay (EBL) located in the Junction Block

When the button is depress to the ON position, current is directed to the rear defogger grid lines. A yellow indicator within the center of the button will illuminate while the defogger is ON. The heated grid lines will heat the rear glass and clear the window surface of fog or frost.

CAUTION: Grid lines can be damaged or scraped off 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.

REAR WINDOW DEFOGGER RELAY
The rear window defogger relay is an electromechanical device that switches fused battery current to the rear glass heating grid and the Light-Emitting Diode (LED) indicator of the rear window defogger switch, when the Body Control Module (BCM) rear window defogger timer and logic circuitry grounds the relay coil.

The rear window defogger relay is a International Standards Organization (ISO) relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions.

The rear window defogger relay cannot be repaired or adjusted and, if faulty or damaged, it must be replaced.

The ISO relay consists of an electromagnetic coil, a resistor or diode, and three (two fixed and one movable) electrical contacts. The movable (common feed) relay contact is held against one of the fixed contacts (normally closed) by spring pressure. when the electromagnetic coil is energized, it draws the movable contact away from the normally closed fixed contact, and holds it against the other (normally open) fixed contact.

When the electromagnetic coil is de-energized, spring pressure returns the movable contact to the normally closed position. The resistor or diode is connected in parallel with the electromagnetic coil in the relay, and helps to dissipate voltage spikes that are produced when the coil is de-energized.

REAR WINDOW DEFOGGER SWITCH
The rear window defogger control switch and circuit are integrated into the HVAC control assembly. Refer to the HVAC control assembly for additional information.

When actuating the switch it sends a ground signal to the Body Control Module (BCM). The BCM actuates the relay allowing current to flow through the grid lines for fifteen minutes upon initial actuation. Then ten minutes with each subsequent actuation or until either the switch or ignition is turned OFF. An indicating lamp illuminates the rear window defogger switch.