Rear Window Defogger

With the ignition switch in the RUN, voltage is supplied to the rear defogger upper and lower zone relay coil. Depressing the rear defogger switch signals the heater and A/C programmer to provide a ground path for the rear defogger relay coils. The relays energize, closing the contacts and applying voltage to the rear defogger and outside heated mirrors. The rear window and the heated mirrors become warm to remove condensation from the glass surfaces. When the rear defogger is turned on, there is a delay before the upper zone is turned on. There is an additional delay before the lower zone is turned on.

The first time the rear defogger switch is pressed, the solid state timer, located inside the heater and A/C programmer, allows the rear defogger and heated mirrors to operate for approximately 10 minutes. Each time the rear defogger switch is pressed thereafter, the solid state timer resets to operate for 5 minutes. The timer resets to 10 minutes when the ignition switch is turned OFF, then back to RUN. The timer also shuts off when the rear defogger switch is pressed while the rear defogger and heated mirrors are already on. If the vehicle is traveling over 48 km (30 mph) the timer function is disabled.

The programmer will disable both of the defogger grids if the system voltage is low.