defroster tape resistance?

[Darylick]

I've got 2 rear hatch glass, not sure if either one works. but both are very clean and there are no breaks in the defroster tape. I'll be checking resistance knowing infinate and 0 are bad, is there a way to tell if one is healthier than the other?
also I will be selling the extra what would be the value?

Darylick

Life is a Dunghill, everyone stands on there own and speaks out about someone elses.

[tanny]

I can't remember exactly, but I had the instructions for testing the strips and you actually test the voltage(not resistance) across each individual strip, with the voltage decresing as you move across the strip. Hopefully someone here has the exact instructions. If not, I'll try to find them. Victor.

[EScanlon]

Careful, the only way to determine voltage or resistance accross any ONE of the wires / strips is to isolate it from the rest of the circuit. Since the only way to remove it from the circuit is to CUT the tape that is NOT what you want to do.

Referring to the units with the vertical lines. The wiring connects at the top of the glass and the two halves of the grid are connected at the bottom to each other.

Take a general continuity METER not a light and connect it to the two terminals. If you get a tone or the needle deflects telling you that you DO have continuity (i.e. a closed circuit) then you know that AT LEAST ONE wire going down and one going up are good. No tone or indication, then the grid is shot on that one and needs to be repaired.

I'll check my books for a testing procedure.

2¢

[Darylick]

Thank you for getting back to me.
It sounds to me that my best bet is a very careful visual inspection of the tape weight (thickness), and a complete circuit check of continuity I hope it would be rare to have dead spots in the tape. It would be difficult to isolate each line. I know I just repeated what you guys have told me, but incase i didn't understand I could be corrected......excuse me but my limmited electrical skills are showing.

Darylick

Life is a dunghill, everyone stands on there own and speaks out about someone elses.

[EScanlon]

By the way, the reason I recommended a meter instead of just a light is that the light is very susceptible to resistance. The more resistance the harder it is for the light to light up. I've checked a couple circuits with the light that said "open" only to discover when I used my meter that there was SOME connectivity.

The ONLY way I've ever known to check a defroster was to plug it in to 12v and then mist the surface with a water spray bottle. Stand back and wait. When it finally starts evaporating the water along the lines you'll know which lines are active and which are not.

I mention this, because my hatch glass has all but two lines working. Unfortunately, one's on the left and the other is on the right. That means that the resistance check between the halves is about equal, which led me to believe I had a completely functional grid.

By the way the resistance check is done, again with the meter. Find the Resistance check (the one with the OMEGA letter, the symbol for Ohms), then check the first connection spade with the opposite side of the window.

You'll find the interconnecting stripe that ALL of the lines merge into. This is the shunt at the bottom which allows the grid to be a LOOP circuit. (i.e. the current goes in one side and returns on the other without intermediary connections)

Check the Resistance (Ohms) from one connector to the connecting stripe and compare the value with the OTHER connector. This will give you the overal resistance for each SIDE of the circuit. If the numbers are very close together, then the individual sides of the circuit are equal. Meaning: The number of grid lines and their individual resistances MATCH (closely) the corresponding lines on the other side of the circuit. Whether they are ALL intact is another question. (see my third paragraph in this post).

Does my grid work? Relatively well when I've used it. We've not had ice or snow, but we did have SOME frost on the windows. (Besides, anyone driving their car in SNOW or worse yet, ICE should be used as a snowshovel, you're asking for it.) In that case the frost was melted relatively quickly (2 miles at 25mph and 3 miles at 35mph).

Now, the continuity and resistance check only tell you if the resistance grid is closed, and it says nothing about the SUPPLY. Now you need to check the output portion of your fuse-box for voltage. This is what your system is providing the accessories AFTER the fuse.

Disregard taking the measurement at the battery, what you'll get there is the POTENTIAL for the circuit. Measuring at the fuse box you get the ACTUAL voltage immediately after the fuse box. Next when you check it at the point of connection, in this case the two little wires coming out from underneath the Dome Light Plastic Finisher, you'll know what the switch and it's associated wiring are using up. If the difference is over 1v then you have to check your connections. You CAN disassemble the switch. Be careful as there are a couple small items (spring and domed contactor) which fit into the toggle, but many times the problem is there.

As a closing note, remember that the Z has one of the easiest and simplest electrical systems as far as vehicles are concerned. There aren't 2,000 different relays and sensors and ...... to cloud the issue. Yes, it is complex, but it is NOT impossible to understand it.

Hope this helps.

[Darylick]

I should have my z out of the body shop within the next month or 2, and I was going to have the front and rear glass installed before, so I can drive my baby home. The interior won't be in at this time so I'll just do the best I can visually and w/ an ohm meter. and then do further test when I get her home.
I presumed that the z car was equiped with a defroster from factory because of lack of ventalation in the rear of the interior. I agree w/ your comment about snow. but here it is almost middle of may and we just got another 4" in the foothills of colorado in the time it might take to have a couple of beers at local Grog shop. so my intention is not to leave her cold but the weather here no one can predict.
Thanx again
darylick

[tanny]

Click on graphic to view larger image.
Fig 18 - Testing Rear Window Grid with a DMM Run the engine at idle and set the rear window grid switch to "ON". Connect the black lead from your DMM to one of the vertical "bus bars" and the red lead to the other bus bar. With the meter set to measure DC volts, the display should indicate 10 to 14 volts; a lower reading indicates a loose ground wire. With the black lead of the DMM grounded, touch each grid wire at its midpoint with the red lead. A reading of approximately 6 volts identifies a grid with no opens. A reading of 0 volts indicates the current path is broken between the midpoint and the battery side of the grid. A reading of 12 volts indicates that the circuit is open between the midpoint of the grid line and ground.


You can attach a piece of aluminum foil to the black lead and run the foil over the grid line with your finger instead of scratching it with the probe. As you run from bus to middle of grid line the voltage drops as above. This did work on my z and escort. However, when I repaired the grid lines with the metallic paint, those grid lines worked, but not as well as the undamaged lines. Good luck.

[24OZ]

There is a lot of intelligent discusion going on over this, I didn't want to lower the tone but I'm going to butt in anyway

I am not sure if you guys have this product in the US, in fact i will be very surprised if you don't, it is a special paint specifically designed for the wire element on the rear demister. All you do is paint this special conductive paint over the element and hey presto... your rear demister should work! Wouldnt this eradicate the need to be getting voltegage meters and Ampmeters and other sensitive electronic gizmos out??? Or have I missed the point?

[Darylick]

Tanny I printed a copy of your post hopefully it doesn't come to that much testing.
Hey george, I've got 2 rear glass and as far as I know they both work I was hoping to figure out if one was in better shape than the other before I install one.
I'm thinking I'll have to chose one with a visual and continuity inspection and install it before I'll know the true shape it's in.
Thnx again

Darylick

[tanny]

240z,

That's fine if you already know where the break is, otherwise you might have to paint the whole grid if you do it randomly, and trying to paint a decent looking straight, thin line(even with the tape or the cardboard template method) with the metallic paint was tough for my mediocre skills. Actually it looked kind of crappy also because the paint was clearly a different color than the original grid. Being fairly anal here. If you really want to be a pea brain, go out and buy one of those little 12 volt space heaters(supposed to warm up the car: not a remote chance here in Colorado, as you would know) in the hope that it will defrost your window(I wouldn't have ever been that stupid). Well anyway, good luck.

After all this babble, I would think that whether the defroster grid works well or not would have a large influence on the hatch value. I know I would not want a hatch that had no heat. You can probably get an idea of used prices from ebay, as they are sold there fairly often.