Heated Glass Element: Description and Operation
REAR WINDOW DEFOGGER CONTROLDescription
The EMIC contains an integral timer and logic circuit to perform the rear window defogger timer and control functions for the optional rear window defogger system. The EMIC uses a hard wired input from the rear window defogger switch on the rear window defogger switch sense circuit and its control logic to determine the correct output to the rear window defogger relay. The EMIC controls the ground path of the rear window defogger relay control coil through an output on the rear window defogger relay control circuit. The EMIC is programmed to interpret each momentary ground signal it receives on the rear window defogger switch sense circuit as a request to change the current state of the output on the rear window defogger relay control circuit. Therefore, with the ignition switch in the ON position, the first ground input on the rear window defogger switch sense circuit turns the system ON, the second ground input turns the system OFF, and so forth. Once the rear window defogger system has been turned ON, it can be turned OFF manually by depressing the rear window defogger switch a second time or by turning the ignition switch to the OFF position. The timer function of the EMIC will also automatically turn the rear window defogger system OFF. The timer turns the system OFF after about ten minutes of operation; however, after the first timed interval has expired, each time the system is turned ON again during that same ignition cycle, the timer will automatically turn it OFF after about five minutes of operation.
The hard wired input and output of the EMIC rear window defogger control can be diagnosed using conventional diagnostic methods; however, there are no other diagnostic tools available for the EMIC rear window defogger timer and logic circuitry. If the input and output components and circuits of the rear window defogger system test OK, but the system fails to operate, the EMIC must be replaced.
Operation
The timing circuit for the Rear Window Defogger is contained internally within the cluster. When the ignition is ON, the first actuation of the Rear Window Defogger switch initiates a 10 (ten) minute time cycle. After 10 (ten) minutes of the same ignition cycle has elapsed, the cluster will turn the defogger off by opening the ground to the Rear Window Defogger Relay. If the defogger switch is actuated a second time during the same ignition cycle, the cluster will turn the defogger off after 5 (five) minutes. While the defogger is on, depressing the switch a second time will turn the defogger off. If the ignition is turned off while the defogger is operating, the defogger will remain off when the ignition is cycled.