Checking the operation and repairing the rear window defroster (BMW 5 Series E28)

The rear window defroster consists of several horizontally located elements on the glass surface.

Minor damage to the element can be repaired without removing the rear window.

Checking the work

1. Turn on the ignition and rear window defroster.

2. Place the positive probe of the voltmeter on the heater element closest to the power source.

3. Wrap a piece of aluminum foil around the negative probe of the voltmeter on the positive side of the suspected faulty cell and slowly move the probe toward the negative side. Watch the voltmeter needle - when it moves from the zero point, the cell is broken at that location.

Repair

The repair is carried out directly on site using a repair kit recommended specifically for this purpose, such as BMW repair kit No.81 22 9 (or its equivalent). This kit contains plastic conductive epoxy. Below are general instructions for this type of repair; if the instructions included with the repair kit differ from those below, follow the instructions in the kit.

1. Before you begin repairing the element, turn it off and let it cool for a few minutes.

2. Lightly sand the surface of the element using fine sandpaper, then clean it thoroughly.

3. Use masking tape to seal the area to be repaired, leaving a gap for applying epoxy resin.

4. Mix the epoxy resin thoroughly according to the instructions on the package.

5. Apply epoxy material into the gap left in the adhesive tape, overlapping the undamaged area by approximately 20 mm on each side.

6. Allow the repaired area to cure for 24 hours before removing the tape and using the rear window defroster.