Rear defogger does not work. 1998 Accord LX 4 door.

1) When you push the defrost button on the front dashboard, the light on the button comes on. But the rear window stays frosted up.

2) I took the rear panels off so I could get access to the wires going to the rear windows, but I was not sure what resistance I should measure from one side of the window to the other side ( connector to connector).

3) It was a year ago, when I last tried to find the problem and gave up. I think I also tried to pull the connectors off the window and see if I could get voltage out of the wires, and it seemed I did not. But I could have been trying to get voltage from the connector to chassis GND and did not get good contact. Next time I think I will try wire to wire ( one side connector to the other). Is this the right idea?

4) I am going at it again before it gets cold. Is there a rear defroster relay that could have gone bad? What should I check? I assume I should get 12 volts out of one of the wires going to the rear window. If not, what should I look for? Could the defrost button on the front panel be bad in spite of the fact the the light comes on the button when you push it down?
BTW I did check the fuse... but maybe I should just put a new one in just to make REAL sure it is good.

Any other advice ??

Thanks!

 

1. With the ignition ON and the defogger switch ON, you should get ~ 12 volts at the positive terminal on the rear defogger.

2. There is a defogger relay located in the passenger side fuse/relay box. However, I wouldn't replace that without testing; in addition, it may not be the issue at all.

Yes, check the under-hood Fuse No. 53 (40A) for the defogger relay. I wouldn't replace it if it is not blown.

3. In the trunk, under the rear shelf, you should be able to see the window antenna coil. There will be two brown electrical connectors plugged into antenna coil. One connector on the driver's side has two wires (Blk/Grn and Blk wires), the other connector on the passenger side will only have one wire (Blk/Grn).

Unplug the passenger side brown connector with only the one wire (Blk/Grn) from the coil box. With the ignition ON and defogger switch ON, measure if there is ~ 12 volts on the Blk/Grn wire. Voltmeter red lead to Blk/Grn wire and voltmeter black lead should be touching body ground.

If there is ~ 12 volts, the defogger relay and wiring up front is okay.

 

Thank you for this information!

I printed it out and will keep it on hand. Need my daughter to let go of the car for an hour or two!

Will post new results when I get to it.

 

Here is a photo of the window antenna coil. Power has to feeds through the coil to the rear defogger.

Connector A is where power (+) comes via the window defogger relay from up front. Connector B is after the power passes through the coil, and then to the defogger.

 

Now I am really baffled !!!

Here is what I have so far:

1) Disconnected wires on both sides of rear window. 12V is coming out on passenger side wire.
2) Connected the passenger side to rear window and measured volts on driver side. 12V coming out of prong!!
so that says current is going through the lines on the rear window!

So the only things I can think of is:

a) All the lines in the rear window are bad, except for 1... which allows the current to flow, but not enough to clear up the rear window. i do see the "dark film" (tint) is peeled in some places and maybe this damaged some of the lines?

b) Maybe the wire going from the driver side rear window (which is the return to gnd?) is bad? Does this wire go to the ant coil connector B as shown in pic in previous post? If so I need to go back and check and see if the wire is broken?

 

When you open the circuit on the drain side (blk wire) there is no current flow so you will see 12V on both sides of rear window defroster. To see a reduced voltage on drain side, you will need to back-probe the connector on drain (black wire) connector w/ the connector mated. This assumes remainder of circuit is good.

Blk/Grn is supply side voltage and should always have 12V as long as heated window circuit is On.

To determine if some of the films on window are open, you have to probe along the length of the film to find the spot where voltage abruptly jumps from drain side voltage to supply side (12v) or vice versa. At that location should be some indication of physical damage to film. You should have at least one intact element, since you measured 12V on drain side blk wire.

If someone removed old tint film w/ scraper, all the heater element lines will be damaged.

good luck

 

I thought if the drain side is open (disconnected) and there is a break in the line on the window, I should not get any voltage when i plug the 12 volts into the window. It would be the same as if I disconnected the 12 v going in, I would not get any measurements on the drain side.

Also... I disconnected both wires and I got 1-2 ohms prong to prong on the rear window. That says the lines ( or just ONE) line are/is ok.

I guess my next step is to see if i get volts going from wire with 12V to the drain wire. both wire will be disconnected and i will measure the volts from wire to wire. That should tell me if the drain side is good or not.

If it is good, I am going to assume there is something wrong with the rear window. The fact that I get 12 volts going into the rear window, says that everything before that wire is OK.

 

"I thought if the drain side is open (disconnected) and there is a break in the line on the window, I should not get any voltage when i plug the 12 volts into the window. It would be the same as if I disconnected the 12 v going in, I would not get any measurements on the drain side."


comment: Filaments are in parallel. You will get 12v if even one of filaments is intact. Since you measured composite resistance of entire filament network at 1-2 ohms, at least one filament is intact. So you should get 12v w/ drain disconnected, if supply side has 12v.


See my previous comment on how to locate defects.


good luck

 

OK, I am going to assume the wires in the rear window is damaged.

For one, there is a tint film that is bubbling in several places, so it may have damaged the wire on the window where the bubble is.

Since the film is covering the inside of the window, I really can't get contact of the wires on the rear window.

Next plan is to turn the car around when there is a hailstorm and hope the hail breaks the rear window~!

Thanks to everyone to gave me advice! Learned a lot here!

 

Your positive voltage check on drain side proves one or more elements are good. You can penetrate old film to make contact w/ element using a sharp pin as a probe.


You can remove the old tint w/o damaging the films any more. Wet w/ water and ammonia mix, place black plastic bag film over the water. Allow to warm for 15 mins and you should be able to peel the old film away. A second moistening/warming may be necessary to get it all.


good luck