The rear window defogger system consists of the following components:

When you turn the ignition to the ON position, battery positive voltage is supplied through the R/DEFG fuse to the rear defogger relay switched input. Ground for the rear window defogger grid and rear defogger relay coil is provided by G301. Battery positive voltage and ignition voltage is supplied to the HVAC control assembly for rear window defogger operation. When the rear window defogger switch is depressed, the HVAC control assembly energizes the rear window defogger relay by supplying ground to the defrost relay coil. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear defogger relay coil. The rear defogger relay energizes and allows battery positive voltage from the switched input through the switch contacts and out the relay switched output to the rear window defogger grid. The HVAC control assembly also illuminates the rear window defogger indicator upon this request.

When you turn ON the ignition and press the rear window defogger switch for the first time, the defogger cycle lasts 10 minutes. Further operation results in 5 minute defogger cycles. The defogger cycle resets to 10 minutes when you cycle the ignition to the OFF position and then back to the ON position.