Rear window defroster

The defrost grid, a screen-printed pattern on the inner face of the glass, may accidentally break, rendering the affected section of the circuit ineffective.

The exact location of the break can be determined using a voltmeter.

Such damage can be repaired using rear window defroster repair varnish, sold under reference M.P.R. 77 01 421 135 (2 g pack).

DETERMINING THE EXACT LOCATION OF THE BREAK USING A VOLTMETER

Switch the ignition on.

Switch on the rear window defroster.

DETECTION BETWEEN LINES B AND A

Connect the voltmeter positive lead to the positive supply terminal of the defroster.

Place the voltmeter negative lead on a filament at the negative terminal side of the defroster (line B); the voltage should be approximately equal to battery voltage.

Move the negative lead towards line A (arrow): the voltage drops gradually.

If the voltage drops suddenly, the filament is broken at that point (repeat for each filament).

DETECTION BETWEEN LINES C AND A

Connect the voltmeter negative lead to the negative terminal of the defroster.

Place the voltmeter positive lead on a filament at the positive terminal side (line C); the voltage should be approximately equal to battery voltage.

Move the positive lead towards line A (arrow); the voltage drops gradually.

If the voltage drops suddenly, the filament is broken at that point (repeat for each filament).

REPAIRING THE FILAMENT

Clean the area to be repaired to remove any dust or grease, preferably using alcohol or glass cleaner, then wipe with a clean, dry cloth.

To obtain a neat line when retouching, apply adhesive tape on both sides of the area to be repaired, leaving the conductive line exposed.

Before using the varnish, shake the bottle so that no silver particles settle at the bottom.

REPAIR

Using a small brush, touch up the area and apply a sufficient coat. If applying successive coats, allow drying time between each coat. Do not repeat the operation more than three times.

If a run or excess material has formed, remove it with the tip of a knife or a razor blade, but only after several hours, once the product has fully cured.

The masking tape used as a guide must only be removed about one hour after application. Pull the tape off perpendicular to the edge, in the direction of the arrow. The varnish, used at an ambient temperature of 20 °C, is fully dry through in three hours. At a lower temperature, the drying time increases slightly.