Rear Window Defogger

The Rear Defogger System consists of Defogger Relay, Rear Defogger grid, Heater and A/C 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 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 Programmer to turn off the defoggers through the UART data line. The 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 Programmer grounds the Defogger Relay's coil , the relay energizes. The relay now closes its contacts, allowing voltage from Maxi(R)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.