Circuit Operation

With the Ignition Switch in "RUN," voltage is supplied to the Rear Defogger Upper and Lower Zone Relay Coil. Depressing the Rear Defogger Switch signals the HVAC 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 (Oldsmobile only) become warm to remove condensation from the glass surfaces. The first time the Rear Defogger Switch is pressed, the solid state timer (in the HVAC 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 minuteswhen the ignition Switch is turned "OFF," then hack to "RUN." The timer also shuts off when the Rear Defogger Switch is pressed while the Rear Defogger and Heated Mirrors are already on.