Rear Window Defogger System Components (w/CJ2)
The rear window defogger system consist of the following components:
| • | HVAC control module |
| • | Body control module (BCM) |
| • | Rear window defogger grid |
Rear Window Defogger Operation
Battery positive voltage is supplied through the RR DEFOG fuse, in the instrument panel electrical center, to the RR DEFOG relay switched input. Ignition voltage is supplied through the HVAC fuse, in the instrument panel electrical center, to the RR DEFOG relay coil. When you start the engine, and depress the rear window defogger switch. The HVAC control module illuminates the rear window defogger indicator and sends a class 2 message to the BCM to enable the rear window defogger system. The BCM energizes the RR DEFOG relay by grounding the control circuit of the relay. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. Ground for the rear window defogger grid is provided by G301.
When you start the engine and press the rear window defogger switch for the first time, the defogger cycle lasts for 15 minutes. Further operation results in 7.5 minute defogger cycles. The defogger cycle resets to 15 minutes when you cycle the ignition to the OFF position and then start the engine.
Rear Window Defogger System Components (w/oCJ2)
The rear window defogger system consist of the following components:
| • | HVAC control module |
| • | Body control module (BCM) |
| • | Rear window that has a number of grid lines |
Rear Window Defogger Operation
Battery positive voltage is supplied through the RR DEFOG fuse, in the instrument panel electrical center, to the RR DEFOG relay switched input. Ignition voltage is supplied through the HVAC fuse, in the instrument panel electrical center, to the RR DEFOG relay coil. The BCM supplies 12 volts on the secondary rear window defogger switch signal circuit to the HVAC control module. The BCM monitors this voltage on the secondary rear window defogger switch signal circuit. When you start the engine, and depress the rear window defogger switch. The HVAC control module illuminates the rear window defogger indicator and grounds the secondary rear window defogger switch signal circuit. The voltage is pulled low on the secondary rear window defogger switch signal circuit, which the BCM interprets as a request for the rear window defogger system. The BCM enables the rear window defogger system by grounding the control circuit of the RR DEFOG relay. This energizes the RR DEFOG relay and allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. Ground for the rear window defogger grid is provided by G301.
When you start the engine and press the rear window defogger switch for the first time, the defogger cycle lasts for 15 minutes. Further operation results in 7.5 minute defogger cycles. The defogger cycle resets to 15 minutes when you cycle the ignition to the OFF position and then start the engine.
