Heated Glass Element: Description and Operation
WINDOW DEFOGGERRear Window Defogger System Schematic:
The Rear Window Defogger electrical system involves the operation of the Manual Temperature Control (MTC) or Automatic Temperature Control (ATC) 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.
Vehicles equipped with an electrically heated rear window defogger also have a 90 amp generator.
ATC Control Head:
The passenger can push the Rear Widow Defogger button on the MTC or ATC head to defog the rear glass. The system will only operate when the ignition switch is in the run position. Once the Rear Window Defogger button is pushed, the button indicator will light and the system will operate for a period of time and then automatically turn off.
When the rear window defogger relay is ON, current is directed to the rear defogger grid lines. The heated grid lines heat the rear glass to dear the surface of fog or frost.
Circuit protection is provided by a fusible link, located in the charging circuit, for the heated grid circuit and by a fuse for the relay control circuit.
The MTC or the ATC head sends a signal to the BCM, which indicates to the BCM that the operator wants the rear window grid to heat. An output wire from the BCM connects to the coil of the rear window defogger relay. The other side of the coil is connected to a fuse. The BCM turns on the relay by connecting the output line of the BCM to vehicle ground. The relay contacts will then dose supplying vehicle power to the rear window defogger grid.
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.