The rear defroster in my car only works on certain grid lines. The top three work, the next three (right in the middle) dont, the next three work and the bottom three don’t. Is this caused by a break in one of the grid lines? Each of the lines? Or perhaps a connection problem somewhere? Any ideas would be appriciated. It just seems odd that it is not one line here or there not working but groups of three.
I haven’t had a chance to see if there is a break on any of the lines.
I know they sell patch kits to fix breaks in the lines but I am not sure if that is the problem. BTW, how well do they work? Easy and quick to use?
If any of the lines are working, the power and ground are okay and there is break somewhere. Most likely each of the three non-working lines has a break, though it’s possible there’s a “trunk” line to those three which is broken. Sometimes the break(s) can be found with visual inspection, but the reliable way to find them is with a test light. Turn on the ignition (shouldn’t need to start the car) and turn on the rear defroster. Clip the test light’s wire to ground and GENTLY run the probe over the lines (they are delicate). One side of the grid is positive and will light up the test light. Work from that end of the lines, when the light goes out you’ve found the break. There might be more than one break in a given line, but the test light can’t find a second break until the first break is repaired or jumpered across.
The patch material usually works well. It’s not hard to use, but attention to detail can be important. Read the directions carefully.
Sounds like broken gridlines to me. There are two ways to detect the break: Visually, or with a voltmeter. Visually is obvious; you look carefully at every inch of the line, trying to spot the break.
With a voltmeter, you turn on the defroster, then touch one voltmeter lead to the vertical bar at one edge of the window. Slide the other voltmeter lead along the gridline; when the voltage suddenly drops from twelve (or so) to zero, you’ve just crossed the break.
The repair kits are just a conductive paint in a little bottle with a brush in the cap, plus some masking material. You apply the masking tape on either side of the broken gridline (to make a nice neat edge) and then paint on a couple coats of the conductive paint. Scotch green plaid tape works fine to mask the edge.
Thanks. I figured that there are breaks in the lines but I was kind of hoping that it may be something easier to fix. I’ll try to check it later today visually. If I can’t find any breaks I’ll have to borrow a voltmeter from my friend.
I tried the grid repair kit (the top $19.95 thing) from http://www.frostfighter.com/ff_products.htm and it did not work. The next winter in fact, I went to inspect the repair spots and the dark-brown paint was heavily cracked all the way through, and I touched it with my finger and it came off the glass, onto my hand. It never worked and I applied it during the summer, so I know that it had long enough to cure properly. I posted about it here if it is still reachable with the new board software… the “paint” is dark brown/copper metalflake and has the consistency and smell of fingernail polish.
I was told on another board the only way to repair such damage was to clean off the ends of the strips with steel wool, and then crazy glue a piece of thin copper wire across them (use the crazy glue on the center of the wire, not eh ends), and then cement the ends of the wire to the ends of the strip with model paint gloss saturated with colloidal silver. I have not tried that yet, as it’s been too cold–the start of this winter was when I found that the repair stuff just flaked off.
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Just a warning note: The heater takes a lot of juice, (they are expected to be on only when driving,) so when your working on it you may run your battery down.