For 1990-2009 cars

### Rear Window Defogger System Components (Oldsmobile)

The rear window defogger system consist of the following components:

• | HVAC control assembly

• | Antenna amplifier module

• | Antenna choke

• | RR DEFOG relay

• | Rear window defogger grid

### Rear Window Defogger Operation

Battery positive voltage is supplied through the RR DEFOG fuse in the underhood fuse block to the RR DEFOG relay switched input. With the ignition in the ON position, ignition voltage is supplied through the HTR-A/C fuse in the underhood fuse block to the HVAC control assembly and the RR DEFOG relay coil. When you depress the rear window defogger switch, the HVAC control assembly illuminates the rear window defogger indicator and grounds 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 antenna amplifier module and then to the rear window defogger grid. Ground for the rear window defogger grid is provided by a antenna choke.

When you start the engine and press the rear window defogger switch for the first time, the defogger cycle lasts for 10 minutes. Further operation results in 5 minute defogger cycles. The defogger cycle resets to 10 minutes when you cycle the ignition to the OFF position and then back to the ON position.

### Rear Window Defogger System Components (Pontiac)

The rear window defogger system consist of the following components:

• | HVAC control assembly

• | RR DEFOG relay

• | 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 underhood fuse block to the RR DEFOG relay switched input. With the ignition in the ON position, ignition voltage is supplied through the HTR-A/C fuse in the underhood fuse block to the HVAC control assembly and the RR DEFOG relay coil. When you depress the rear window defogger switch, the HVAC control assembly illuminates the rear window defogger indicator and grounds 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 is provided by G402.

When you start the engine and press the rear window defogger switch for the first time, the defogger cycle lasts for 10 minutes. Further operation results in 5 minute defogger cycles. The defogger cycle resets to 10 minutes when you cycle the ignition to the OFF position and then back to the ON position.