If the glass surface remains uncleaned after switching on the electric heating, check with a test lamp or a voltmeter whether there is supply voltage at the terminals of the glass heating element. To do this, use a test lamp (or a voltmeter) connect to the "+" terminal of the electric heater and the "ground" of the body. If there is no supply voltage, check the wiring of the power supply circuit of the element and eliminate the malfunction.
If the heating element power supply circuit is in good condition, check the condition of its conductive strips.
The test is carried out with the engine running and the electric heating on. Using a voltmeter, measure the voltage on all the strips one by one, connecting one terminal of the voltmeter to the body "ground" and the other one in series to the conductive strips. If the voltage measured by the voltmeter at the beginning and end of the strips is the same and approximately equal to the battery voltage, check the reliability of the contact of the "ground" wire of the heating element with the car body.
The voltage on the strip should decrease as the voltmeter connection point moves away from the positive polarity bus of the element. The voltage should be measured in at least two places at the same distance from the axis of symmetry to eliminate the possibility of missing a damaged section. If you find a discrepancy in the readings on one of the strips, move the contact of the voltmeter wire along this strip until the voltage becomes zero. A sharp decrease in voltage indicates a break in the strip at this point. Mark the break on the outer surface of the glass with chalk or a glass graphite pen for subsequent repair of the damaged section.
To repair the heating element, you can use one of the special kits available for sale. Despite the fact that the kits are made by different manufacturers, their composition is approximately the same, and they all come with instructions for use. Below is a typical procedure for working with these kits.
1. Remove a 6mm long section of the strip from each side of the damaged area.
2. Wipe the damaged area with a clean cloth soaked in alcohol.
3. Apply repair adhesive tape or two pieces of regular adhesive tape to the glass at the damaged strip location, above and below the area being repaired, with the distance between the pieces of adhesive tape corresponding to the width of the conductive strip on the glass.
4. Mix the hardener thoroughly with the silver base compound. If the hardener has thickened, place the package in hot water and wait until the hardener becomes liquid.
5. Apply the composition to the area to be repaired using a wooden spatula and remove the adhesive tape.
6. Place the heater at a distance of 25 mm from the damaged area and heat the composition for 1-2 minutes.
Note: In some kits, the composition does not need to be heated: it polymerizes at room temperature.
7. If the strip has become discolored after drying, apply a tinting iodine composition to it with a brush - the color of the strip will be restored. After the iodine composition has dried for 30 seconds, wipe off its excess with a clean, lint-free cloth. During the entire polymerization time of the repair composition, which lasts 24 hours, exclude any mechanical impact on the repaired section of the strip.
8. Turn on and check the operation of the rear window heating element.
If the wire has come off the busbar, solder it with solder containing 3% silver and rosin paste as flux in the following order.
1. Clean the soldering area on the busbar and the wire core.
2. Apply a little rosin paste to the areas of the wire and busbar to be connected using a brush.
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3. Apply a thin layer of solder to the wire core.
4. Solder the wire to the busbar, avoiding overheating of the parts being connected.