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Old 01-05-2014, 06:02 AM   #1 (permalink)
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Question defroster grid not working

Hey all,
hope someone can help because it is currently very cold up here in cleveland and suddenly my defroster doesn't work. Projected for a bit more snow and temps down to -13 this week so any help you can give would be great.
Here are the details I have.
I have a 2005 outback 2.5XT limited. MT. it has heated side mirrors, wipers and rear defroster. None of them seem to work. Just noticed it about a week ago. I checked the fuses both in the kick panel and under the hood that seems to be associated (fuse 10 under the hood and 22 under the dash) both are intact. Didn't do anything with the relay but when I press the defroster button it lights up and kicks off with the timer like it should and I can hear the relay clicking on and off so I figured it was okay.
I did find a thread about broken wires in the boot running to the lift gate but that seems less likely to me because it would seem if the wire was broken back there I should still have the mirrors and wiper blade warmers working right?
Have not checked for current across the grid but I did visually inspect it and i don't see any breaks.
Please help, what could this be?
thanks
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Old 01-05-2014, 08:27 AM   #2 (permalink)
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The rear defogger and mirror heaters are electrically dependent; the mirror heaters are powered, in part, from the rear defogger system. But the wiper deicer (actually a heater in the lower part of the windshield) is not dependent on the defogger system -- it can be operated independently. So the odds of both systems failing at the same time would seem to be low.

There is a common factor to all three, namely the "timer" that you mention. (This is part of the Body Integrated Unit, or "BIU".) However, if either the wiper deicer switch or the rear defogger switch is turned On, and the "on" light goes out after 15 minutes or so, then the related timer in the BIU is working, and that would seem to eliminate the BIU as a factor. (Also, the fact that the relay(s) seem to be working (click) when either the wiper deicer switch or the rear defogger switch is turned On and Off manually would tends to verify the continuity of the timer circuit.)

The broken wires going to the rear hatch can seem to have odd effects, some totally unrelated. So it's not outside the realm of possibility that a broken wire is affecting all the heaters. But I'm less inclined to focus on this at this point.

Which brings me to a question: How are you checking if the heaters are working? I ask because in extreme cold, the electrical system is under more load (battery capability is reduced, alternator has to work harder) and therefore the heaters will not be as effective as they might be at other times. It can take a lot longer before the effects on interior surface mist, and exterior snow or ice, tend to show. All the more so if the battery or alternator is weak, or there are poor connections in the electrical system, to begin with.
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Old 01-05-2014, 08:27 PM   #3 (permalink)
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as far as I know my wiper deicer is tied to the mirror and rear window defoggers. My wiper deicer is not a heater setting that is blown near the wipers but another set of painted strips on the front windscreen that sit under where the wipers park.
As for testing. I only have anecdotal evidence. It is not that the mirrors and rear window are slow to defog but that in the entire 15 min cycle (and if it is a long trip I usually turn it back on after it turns off) i don't notice any difference at all. No snow is melted and only minor decrease in fogging on rear window only, but I am inclined to think that the reduction in fog on the rear window is more due the the entire cabin being warmed than the defogger working.
I hadn't considered a weak battery and will get that tested tomorrow. thanks
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Old 01-05-2014, 08:40 PM   #4 (permalink)
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On the '05 XT, the wiper deicer has its own switch. It lives just below the dimmer for the dash lights. As for the rear defogger, I would think it's just too cold for it to work effectively. I have never experienced temps that low, so I can't say for sure.

Both functions have a 15 minute timer, so you might need to restart them under severe conditions.
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Old 01-05-2014, 09:00 PM   #5 (permalink)
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If the car was parked, and then driven in blistering cold temperatures, it would take a lot more heat (BTUs) to raise the temperature of the glass enough to melt/dissipate the coatings on the surface.

The heaters can be checked with an IR thermometer fairly easily if the car is parked in a sheltered area (e.g. garage). The IR thermometer will detect even a small change in temperature. Start the car, measure the temperature of the mirror/lower windshield/rear window (should be close to ambient) then turn on the heaters. The temperature of the glass in the area of the heater strips (there are strips on the back of the mirrors as well) will normally start to increase noticeably in 15-30 seconds. Just this change is enough to confirm that the heaters are working.
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Old 01-05-2014, 09:14 PM   #6 (permalink)
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Quote:
Originally Posted by Radar View Post
As for the rear defogger, I would think it's just too cold for it to work effectively. I have never experienced temps that low, so I can't say for sure.
We had temperatures of -28F this week and the rear defogger still works very quickly. It's very efficient having the elements in contact with the glass.
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Old 01-06-2014, 03:32 AM   #7 (permalink)
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I stand corrected. It has been a while since i needed to use my wiper deicers and I had totally forgotten that they were on a separate button. Will have to wait for more snow to test them but the light does come on so they may be just fine. now just have to get the defogger working and I will be happy
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Old 01-06-2014, 07:31 AM   #8 (permalink)
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Quote:
now just have to get the defogger working and I will be happy
If it's only the rear window defogger that isn't working, then the possibility of it being due to a broken wire in the flexible boot to the hatch is higher.
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Old 01-07-2014, 10:35 AM   #9 (permalink)
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So I had my battery tested and it did test bad. Had it replaced and it did not seem to fix the defogger/mirrors. Wasn't able to test the wiper deicer because there was no ice yet. will test today. would a broken wire in the boot affect both the rear defogger and the mirrors?
thanks
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Old 01-07-2014, 11:23 AM   #10 (permalink)
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Not likely.

Broken wires to the rear gate have been reported to cause unexpected symptoms, so I can't say it's impossible.

In order for the mirror heaters to work the rear defogger has to be on. If a fuse in the defogger circuit is blown, or the defogger relay is bad, that could prevent both from working.

This recent thread (07 Hatch Wiring Harness - Connecter Question) is about the broken wires, and has links to several earlier threads on the same topic, some with photos of the broken wires. Might be worthwhile looking through them to get an idea of what to look for.

Also, see if you can check for power at fuse #10 (25 Amps) in the engine compartment fuse box. It should have power when the rear defogger switch is ON.
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