The rear window defogger system consists of a rear window with 2 vertical bus bars and a series of electrically connected grid lines baked on the inside surface. A control switch and a timer relay combined into a single assembly is used on all models.
All circuit protection is provided by a fusible link, located in the charging circuit, for the heater grid circuit and by a fuse for the relay control circuit.
NOTE:Since the grid lines can be damaged or scraped off with sharp instruments, caution should be used when cleaning the glass or removing foreign materials, decals or stickers. Normal glass cleaning solvents or hot water used with rags or toweling is recommended.
DIAGNOSIS & TESTING
The rear window defogger system operation can be checked in the vehicle using the following test procedure:
- Turn the ignition switch to the ON position, also turn the rear window defogger control switch to the ON position.
- Monitor the vehicle ammeter. With the control switch in the ON position, a distinct needle deflection should be noted.
NOTE:If the vehicle is not equipped with a voltmeter or a ammeter, the rear window defogger operation can be checked by feeling the glass in the rear windshield. A distinct difference in temperature between the grid lines and adjacent clear glass can be detected in 3-4 minutes of operation.
- Using a DC voltmeter, connect the vertical bus bar on the passenger side of the vehicle with the positive lead and the driver side of the vehicle with the negative lead. The voltmeter should read between 10-14 volts.
- Only Steps 1, 2 and 3 will confirm the system is operational. The indicator or pilot light illumination means that there is power available at the output of the relay only and does not necessarily prove the system is operational.
If the rear window defogger system does not operate properly, the problem should be isolated as outlined in the following procedure:
- Check to be sure the ignition switch is in the ON position. Be sure that the rear defogger feed (HOT) wire is connected to the terminal or pigtail and that the ground wire has a good ground.
- Be sure the fusible link and control circuit fuse is operational and all electrical connections are secure. If all of these things have been completely checked out, then the following may be defective: the control switch/timer relay module or the rear window defogger grid lines.
- If the grid lines were to blame, either all the grid lines would have to be broken, or the feed (HOT) wires are not connected for the system to be inoperative.
- If turning the control switch procedures give severe voltmeter (ammeter) deflections, check the system for a shorting condition. If the systems check out but the indicator bulb does not light, check and or replace the bulb.