2. Minor damage to the heating elements can be repaired without removing the rear window.
Examination
3. Turn on the ignition, then turn on the rear window defroster.
4. Connect a voltmeter to the positive and negative terminals of the heater. If the voltmeter does not indicate battery voltage, check the fuse, switch, heater receptacle, and related wiring. If voltage is present, however, all (or part) heating elements do not work, do the following.
5. When measuring voltage in the following tests, wrap the voltmeter probe with aluminum foil and press the foil with your finger against the heating element (pic. 22.5). Connect the negative probe of the voltmeter to the negative terminal of the heater.
6. Measure the voltage at the center of each heating element (pic. 22.6). If the voltage is 5-6 V, then the corresponding element is working (i.e. has no gaps). If the voltage is 0, then there is a gap between the center of the corresponding element and the positive terminal of the heater. If the voltage is! 1-12 V, then there is a gap between the center of the element and the negative terminal of the heater. Check each heating element.
7. If all elements are serviceable, connect a negative probe of the voltmeter to the mass of the car. In this case, the voltmeter reading should remain the same. If the voltmeter reading changes, it is necessary to restore the contact of the heater with the mass.
8. To find the break point in the heating element, connect the negative probe of a voltmeter to the negative terminal of the heater. Press the positive lead of the voltmeter wrapped in foil against the heating element, starting at the positive terminal and moving towards the negative terminal. At the point where the voltage abruptly drops from a few volts to zero, there is an open (pic. 22.8).
Repair
9. To repair breaks, you can use a repair kit (e.g. Dupont paste #4917 or similar). The kit contains a special conductive adhesive.
10. Before starting repairs, turn off the rear window defroster and let it cool down for a few minutes.
11. Clean the area around the heating element with a fine wire brush, then wipe the area with methanol.
12. Apply adhesive tape around the area of the heating element to be repaired.
13. Thoroughly mix the epoxy from the repair kit following the manufacturer's instructions.
14. Apply glue to the break and 2 cm of the heating element on each side of the break (pic. 22.14).
15. Allow the composition to dry for 24 hours, then remove the adhesive tape.