Heated Glass Element: Description and Operation

GENERAL DESCRIPTION

Purpose
The rear window and outside mirror defoggers is a standard feature. The system is designed to remove fog and ice from the rear window and outside mirrors, providing the driver with clear rearward vision.

Operation
To operate the rear defogger, the engine must be running, the hard top connector C319 connected or the soft top in the up position, and the rear defogger button on the Climate Control/Driver Information Center (CCDIC) must be momentarily depressed. System activation is indicated by the illumination of the rear defogger annunciator symbol on the CCDIC and the LED in the rear defogger button. Momentarily depressing the rear defogger button again after the system has been turned on will turn the defogger off.

When the system is turned on, power is supplied to heating elements which are imbedded in the rear window and outside mirrors' glass. The heating elements warm the glass, causing the fog or ice to dissipate. The first time the system is activated during an ignition cycle it will operate for 10 minutes. Subsequent activations of the rear defogger after the initial 10 minute cycle will last approximately 5 minutes.

CIRCUIT OPERATION
The Rear Defogger System consists of Defogger Relay, Rear Defogger grid, Heater and A/C Programmer, LH and RH Outside Mirrors, Body Computer Module (BCM), Climate Control/Driver Information Center (CCDIC), Soft Top Position Switch and related fuses and wiring.

When the rear defogger button is pressed, the CCDIC sends a request to the BCM thru the UART data line. The BCM now must confirm that the engine is running, and that either the soft top is in the up position or the hard top connector C319 is connected.

When the soft top is up out of the storage compartment the Soft Top Position Switch is closed grounding the BCM input at terminal 3D9. When connector C319 of the hard top is connected terminal 3D12 of the BCM is grounded verifying that the hard top is in place and connected.

If the soft top is down or hard top connector C319 is disconnected the BCM will command the CCDIC to display the warning message "REAR DEFOG DISABLED."

Once engine running and either soft top or hard top status has been confirmed, the BCM sends one command to the CCDIC to turn on the rear defogger annunciator and one to the Heater and A/C Programmer to turn on the defoggers. Both commands are sent through the UART data line.

When the Heater and A/C Programmer receives the command to turn on the defoggers, the Programmer applies ground to the coil of the Defogger Relay through the transistor driver at terminal M.

Another function of the BCM is the timing cycle function. When the 5 or 10 minute cycle has elapsed, the BCM commands the Heater and A/C Programmer to turn off the defoggers through the UART data line. The Heater and A/C Programmer will then open the relays ground path to turn off the defogger. The BCM will also command the CCDIC to turn off the rear defogger annunciator at this time through the UART data line.

Defogger Relay and Defogger
When the Heater and A/C Programmer grounds the Defogger Relay's coil, the relay energizes. The relay now closes its contacts, allowing voltage from Fuse C3 to be applied to the Rear Defogger and Fuse D11 of the Console Fuse Block. Fuse B11 feeds and protects the Outside Mirror Defoggers and their circuits. When voltage is applied to the heating elements, the elements warm and dissipate any fog or ice.