Rear Window Defogger Operation

CIRCUIT OPERATION
The rear window defogger system uses a relay located in the junction block. This relay is protected by two fuses and controlled by the Body Control Module (BCM). When the operator pushes the ON switch for the rear window defogger a signal is sent to the BCM on circuit C58. The A/C-Heater control uses resistors internal to the unit and the BCM measures the voltage on the circuit to determine operator request. Ground for the control is provided on circuit Z2.

When the signal is processed by the BCM it grounds circuit C80. This is the coil of the relay Power for the coil is provided on circuit F13. This circuit also supplies power for the windshield wipers and combo flasher. Circuit F13 is protected by a 10 Amp fuse in cavity 15 of the junction block and is HOT in the ACCESSORY and RUN position only Power for the fuse is provided on circuit A31 from the ignition switch.

The A31 circuit receives power from the A1 circuit which originates in the Power Distribution Center (PDC) and is protected by a 20 Amp fuse located in cavity 8.

As current flows through the relay, contacts in the relay CLOSE connecting circuits A4 and C15. The A4 circuit is protected by a 40 Amp fuse located in cavity 16 of the PDC. Circuit C15 connects from the relay to the rear window defogger grid and the heated mirrors.

The rear window defogger grid consists of two BUS bars and grid lines that form a parallel circuit. When current flows through the grid the grid lines heat up and transfer the heat to the window. Ground for the grid is provided on circuit Z1 and terminates at the right rear wheel well.

When the system is in operation a Light Emitting Diode (LED) located in the A/C-Heater control is illuminated.