The conductive thread mesh of the glass heater, applied by screen printing on the inside of the glass, can be damaged if handled carelessly, which can result in the corresponding part of the electrical circuit failing.
The exact location of the break can be determined using a voltmeter.
Repair of such faults is possible using varnish for repair of rear window heater, catalog number MPR 77 01 421 135 (packaging 2 g).
Determining the location of a break using a voltmeter
Search in zone A-B
Figure 8.52. Determining a break in the rear window heating element in zone A–B
Turn on the ignition. Turn on the rear window heating.
Connect the voltmeter lead from the positive terminal to the positive terminal of the rear window defroster.
Connect the wire from the negative terminal of the voltmeter to the wire on the negative side of the rear window defroster (line B) – the voltage should be approximately equal to the battery voltage.
Move the negative wire to line A (by the arrow) – the voltage should gradually drop.
A sharp drop in voltage means that the thread is damaged in this place (do this operation for each thread). Mark the damaged area with a marker.
Search in zone C-A
Figure 8.53. Determining a break in the rear window heating element in zone C–A
Original of this article on the website: renaultbook
Connect the wire from the negative terminal of the voltmeter to the negative terminal of the rear window defroster.
Connect the wire coming from the positive terminal of the voltmeter to one of the threads on the positive side of the rear window heater (line C) – the voltage should be equal to the battery voltage.
Move the positive wire to line A (by the arrow) – the voltage should gradually drop.
A sharp drop in voltage means that the thread is damaged in this place (do this operation for each thread). Mark the damaged area with a marker.
Repair of heating filaments
Using alcohol or glass cleaner, clean the repair area to remove dust and grease, then wipe it with a clean, dry cloth.
To obtain a straight line, cover the area to be repaired on both sides with adhesive tape, leaving only the damaged thread itself exposed.
Before applying the varnish, shake the bottle to remove any silvery sediment from the bottom.
Apply a sufficient layer of varnish with a thin brush. If applying several (no more than three) layers, observe the drying time of each layer.
If a drip does form, it can be removed with a knife or razor blade after a few hours, when the product has completely hardened.
Figure 8.54. Removing the adhesive tape after repairing the rear window heating element
The adhesive tape used as a guide can be removed only approximately one hour after application of the product. The tape is torn off by applying force perpendicular to the thread in the direction of the arrow (Figure 8.54). At an air temperature of 20°C, the varnish dries completely after three hours. At a lower temperature, the drying time increases slightly.