Rear Defogger: Description and Operation

Description
The rear window defroster system is comprised of the rear window defroster relay, the filament, the LH and RH power outside mirrors, the rear window defroster switch, and the CPU.

System Operation
^ When the ignition switch is at ON, the CPU applies battery positive voltage from terminal 2T to the rear window defroster switch. If the rear window defroster switch is pressed, current flows from CPU terminal 2T to ground through the closed switch contacts. This signals the CPU to ground the rear window defroster relay at CPU terminal 2S. Voltage from the engine fuse is then applied to the rear window defroster relay coil, and current from the engine fuse flows through the relay coil to energize the relay. The relay's contacts then close and allow power from the defog fuse to be applied to the filaments of the rear window defroster and power outside mirrors. The elements warm to dissipate any fog or ice. The CPU operates the rear window defroster even after the rear window defroster switch is released.
^ The rear window defroster indicator light is powered by the meter fuse when the ignition is at ON. CPU grounds the defroster indicator light to illuminate the indicator while the rear window defroster switch is in the on position.
^ The CPU initially operates the rear defroster for approximately 15 to 17 minutes. After this, the CPU cycles the system off for 3 minutes and then on for 2 minutes while the rear window defroster indicator light continues to illuminate. The rear window defroster system is cancelled and the indicator light goes out when either the ignition or the rear window defroster switch is pressed again.