Rear Window Defogger

The rear window defroster consists of a number of horizontal heating elements bonded to the surface of the rear window glass.

Minor breaks in the elements can be repaired without removing the rear window glass.

Inspection

PROCEDURE
1. Turn the ignition key and the rear window defroster switch to the On position.

2. When measuring voltage in the following two tests, wrap a strip of aluminum foil around the negative voltmeter probe and press the foil against the wire with your finger (1 – voltmeter probe, 2 – defroster grid wire, 3 – foil).

3. Check the voltage at the middle of each heating wire. If the voltage is 5 volts, the wire is good (no break); if the voltage is 10 volts, the wire is broken at a point between the center of the wire and the positive terminal; if the voltage is 0 volts, the wire is broken between the center of the wire and ground.
4. Connect the negative voltmeter probe to vehicle ground. The readings should remain the same.

5. To locate the break point, connect the positive voltmeter probe to the positive defroster grid terminal. Touch the foil-wrapped negative probe to the defroster grid wire as close as possible to the positive terminal, and move the foil along the wire toward the negative terminal. The point at which the voltmeter reading rises from zero to several volts is the break point.
6. If the heating element is not broken, the voltmeter will show no voltage at the positive end of the wire, and the voltage will increase progressively toward the negative end, where it will be approximately 12 volts.

Repair

PROCEDURE
1. Repair the wire break using a repair kit specifically designed for this purpose, available from automotive parts stores.
2. Before starting the repair, turn off the defroster and allow it to cool for several minutes.
3. Lightly abrade the break area with fine sandpaper, then thoroughly clean it with alcohol.
4. Mark the break area with adhesive tape.
5. Repair the wire break following the instructions supplied with the repair kit.