Grand Cherokee 2WD V8-4.7L VIN N (2000)
Rear Window Defogger Switch: Description and Operation
The rear window defogger switch is integral to the heating and air conditioning control unit, which is located in the instrument panel center stack below
the radio receiver. This momentary switch provides a hard wired ground signal to the Body Control Module (BCM) each time it is depressed. A Light
Emitting Diode (LED) in the push button for the rear window defogger switch illuminates to indicate when the rear window defogger system is turned
on.
The rear window defogger switch and the rear window defogger switch LED indicator cannot be repaired and, if faulty or damaged, the entire heating
and air conditioning control unit must be replaced.
When the rear window defogger switch push button is depressed, it momentarily closes the rear window defogger switch sense circuit for the BCM to
ground. The BCM monitors the rear window defogger switch sense circuit. Each time the BCM rear window defogger timer and logic circuitry sees
another input from the switch, it toggles a control output to the rear window defogger relay. Energizing the rear window defogger relay provides
electrical current to the rear window defogger grid and to the LED indicator in the switch, which lights to indicate when the defogger system is turned on.
A dedicated fuse in the junction block protects the rear window defogger relay output circuit to the LED indicator.
