how to modify rear window defrost?

Yeah this is a little annoying coming from my Mazda or was it my Honda that had a hard switch.

But the counterargument is "how many folks leave that thing on all summer as a result?"

I do prefer having a hard switch though. The heated mirrors and the seat warmers appear to operate this way, so they're not even internally consistent on this. Hee hee...

Haven't done it, but I can't imagine it'd be too hard. Before I'd attempt it though, I'd be sure to get hold of the wiring diagram. Good luck!

-- Todd H.

2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA

It shuts itself off after ten minutes, doesn't it? That's usually long enough to get the stuff off, and by then the inside of the car is warm and thst heat does the job. Never thought about it before, otherwise.

-John

The switch is an input to the ECU, which in turn operates the defroster through a relay. It's a momentary/toggle switch and there isn't much you can do to change its operation. I suppose if you are electronically inclined, or know someone who is, it would be possible to build a circuit that would send a momentary pulse to that circuit every time the car was started. But there are considerations such as do you really want it to come on every time you stop and start the car, adding logic to make it only work on the first cold start of the day wouldn't be worth the effort. Another factor to consider is that the defroster puts a heavy drain on the electrical system so it's best to wait until the engine is running for a minute or two before turning it on.

Sorry if I sound like a newbie, athough I am - it makes good sense not to turn the key to accessory, turn the defroster on, then start the engine, as you say. But if the engine is running, how could the defroster load matter? I ask because I generally use it in the morning, and I go in the order: start the engine, turn on the df, set the heat, wait another half a minute for engine warmup, get in gear and go.

Oooh. If that's the case, I wonder if the ECU connection internally is such that hacked ECU firmware could modify this behavior. Muwuhahahahahaha.

Those folks who tweak ECU firmware for performance and all that jazz might be enjoined in such a query

-- Todd H.

2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA

You want this but you really don't want this.

What things like this should be designed to do is to let go or disengage when you turn the Ign off and remove the key.

Just hit the button each time you need it, there are worse things in life.

TBerk need a better (actual) explanation why?

1) you don't live in canada. there are folks south of the border who think they don't even need a rear defrosters - like, it's never cold and damp there. yeah, right! 2) if i want the sucker on, i put the little switch in the "on" position. and leave it in the "on" position until i decide that it should be moved to the "off" position. chances are, tomorrow's weather will be a lot like today's weather. no timers, no bells and whistles, and no "you've had enough, so i'm going to shut it off for silly little old you".

i'm also pissed that subaru decided that i can't run the windshield defog (front heater) on inside air (the little light goes off when you move from lower vents to defog) - obviously, the news flash hasn't percolated through that you can heat up inside air faster than outside air, when the temperature outside is -30. it's the heat on the glass, and not the humidity, that matters. (is anybody from engineering LISTENING?)

3) if i'm stupid enough to ignore a lighted switched for the whole two weeks that are called "summer" up here, i deserve whatever the consequences might be of using a defroster unnecessarily. (20 lashes? public ridicule? guest appearance on letterman?)

....... tom klein

wow! hacking the ecu might actually be fun, and a lot safer than chopping into the wiring harness!

the simplest approach i can think of is to replace the relay, if it's socketed, with a "dud" relay that's always on, wired to an spst switch in series. pop in a good relay, and everything's back to factory spec. and just to make the engine-ears happy, of course i would opt for a lighted switch, too.

where do i find information on the ecu and/or the car's wiring (2002 legacy wagon)?

....... tom klein

Close, though. And I been there lots and lots of times, once driving from Saskatoon to Moose Jaw and the dang car never got warm. -30 that day. The AC plugs in all the parking spaces at the hotel were pretty interesting. Why the hell was I in Saskatoon in February anyway? Dumb idea.

Well, there's something to be said for that. :-)

Warmer, humid air hitting cold glass condenses pretty fast in my experience. I only had an interior fog-up once, in my old Galant. PITA, that was.

OK, well, just hardwire that sucker and be done with it. With only two weeks of summer, you deserve it. :-)

-John O

This doesn't happen on my '01 OBW.

Is that why cars never fog up on the inside in Florida?