Heated Element: Description and Operation

GENERAL DESCRIPTION

Purpose
The rear window and outside mirror defoggers is a standard feature on all Eldorados and Sevilles. 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 and the rear defogger button on the Climate Control Panel must be momentarily depressed. System activation is indicated by the illumination of the rear defogger annunciator symbol on the Climate Control Panel display 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 (HVAC) Programmer, LH and RH Outside Mirrors, Instrument Panel Cluster and related fuses and wiring.

Instrument Panel Cluster and HVAC Programmer
When the rear defogger is turned on, the Instrument Panel Cluster must confirm that the engine is running thru the UART data line. Once engine running status has been confirmed, the Instrument Panel Cluster turns on the rear defogger annunciators. The Instrument Panel also sends a command to turn on the defoggers to the Heater and A/C Programmer via the UART data line. When the HVAC 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 D5.

Another function of the Instrument Panel Cluster is the timing cycle function. When the 5 or 10 minute cycle has elapsed, the Instrument Panel Cluster commands the HVAC Programmer to turn off the defoggers through the UART data line. The HVAC Programmer will then open the relay's ground path to turn off the defogger. The Instrument Panel Cluster will also turn off the defogger-on annunciators at this time.

Defogger Relay and Defogger
When the HVAC Programmer grounds the Defogger Relay's coil the relay energizes. The relay now closes its contacts, allowing voltage from Maxi Fuse 5 to be applied to Fuses B7 and B9 in the Trunk Compartment Fuse Block Fuse B7 feeds and protects the Outside Mirror Defoggers and their circuits. Fuse B9 is a 30 amp fuse which feeds and protects the rear window defogger circuit. When voltage is applied to the heating elements, the elements warm and dissipate any fog or ice.