GoldenBird

Car hasn't been seeing much action, but I've been going out and starting her a few times a week. I noticed today the rear defroster is not working at all. It's actually acting like I didn't even push the button...I forget if when you push it the button stays "down" or it's just the indicator light that goes on, but regardless the light isn't going on and the button stays in the same position. I checked the fuse...which is actually a breaker shared with the power seats. The seats still work and I tried switching in the window breaker (same size) and either way the seats and windows work but no defrost. Any advice? A search revealed a few rear defroster issues people have had but not this one. Thanks.

2001NBMZ28

Hmmm....thinking the breaker can work/reset/work/reset etc. I'd try putting a 30 amp fuse in it's place and see what happens.

GoldenBird

I've seen that recommended in other threads to temporarily test it when it's having a different issue. If it works with a 30 amp fuse is that acceptable for long term use? I'm doubting that'd the issue though.

2001NBMZ28

Should've stated that's just for a test, but people do leave it in - personally I wouldn't. Fuse is just an easy way to test the breaker. If no one else responds with an answer I'll look it up in my helms tomorrow.

2001NBMZ28

Read through the general description/operation in helms - the rear defogger switch/timer is also powered through the HVAC fuse in the IP fuse box for "ignition 3 voltage." Maybe thats blown?

GoldenBird

You lost me at IP fuse box. Is that a second fuse box? Where might I find that? Thanks...I only have thirdgen manuals kicking around!

2001NBMZ28

IP = Instrument Panel - the fuse box inside the car. Without looking at the wiring diagram, thinking it means the switch needs to see voltage with the ignition on.

GoldenBird

The one labeled HVAC was fine...didn't see anything saying ignition 3 voltage though. Any more ideas guys?

GoldenBird

Hmmm...new development. Screwing around with it again now I'm noticing when I push it, a light comes on behind the button. The indicator light still never illuminates at all, but looking through the slight gap between the edge of the actual button and the dash panel it's clear that pushing the button is lighting something up back there for as long as I hold it. WTF?

How do you even get that panel off?

Formula413

iTrader: (1)

There was a similar discussion on this board sometime recently. When I bought my car it had the same problem, when you push the switch the light doesn't come on. That switch does not change position, whether it's on or off it stays in the same place, but it should make a clicking sound. My car ended up needing the whole hvac control because you can't replace just the switch.

ghardester

I had my defogger switch go out on the '01 Bird. Defog no work, switch light don't come on. Bad switch. Formula413 is correct, you have to buy the whole heater/defog/fan switch unit. And that is the bitch of it. Replacement is not that hard. The trim panel around the radio and defog/heat controls just pops off. Use a small screwdriver or something to pry it gently around the edges. Carefully. It should come off fairly easily. There are about 4 tabs on it that just click in. There is no fiddling with the switch that will fix it, but go ahead and try. And later you'll probably have to buy the whole replacement unit. I forgot what I paid but you won't like it.

GoldenBird

So you don't have to get too far into the dash messing with much wiring or anything right? I took the panel off today to get a look and it seems like there's not much room to get your hands back there. Basically all I need to replace is the piece with all the controls (the red/blue dial, AC/Vent/Heat, etc)?

ghardester

Yep, replace that whole unit. It's not hard. No getting too far into the dash wiring. Just pull the old controller out, there should be enough slack in the wires. Reach around the console if you can to help move things out as you pull the unit out. Behind the defog switch is a little circuit board. There's nothing that can be fixed, just replace the whole unit. It's a little tight plugging the new controller in. The Heater controls are a controlled by vacuum tubes, but they all come off as a unit. Just unbolt the old controller and pull as much wire slack out as you can. If you take it to the shop/dealer they will do it in a few minutes and rape your wallet. It's like 3 contections. You have 300+ posts, it will be simple, after you get it done. It's just unplug this unit, plug in the new one. All that's left is the cussing about a faulty Gm part.

Formula413

iTrader: (1)

I wish I had asked the place that changed mine to save the old one, I know a little about electronics, I wonder if I could have found some way to fix that switch with a generic part from Radio Shack or something. If it ever craps out again that will be the first thing I try.

ghardester

Well, I just finished replacing my second, or probably third set of HVAC controls due to the defogger not working! This time on the 2002 WS6. There are several other threads here about replacing the relay with a 30 amp fuse in the fuse box, this may work in situations where the button kicks off too soon and the defogger quits working but it does not fix the problem with a defogger that quits working altogether. Relays can get 'tired' after time and become weaker, so replacing the relay with either a fuse or a new relay can fix the problem with a weak button. I tried replacing the relay after the button quit working, tried swapping the relay with a fuse, but still no light or defog action from the button. Button no light, no work. So new HVAC controls again.

Has anyone found a way to fix the problem with the circuit board behind the defog button on the HVAC controls when the button does not work at all? Something a soldering iron and a few resistors can fix. I've now got a couple of HVAC controls to experiment with. Does anyone have any idea what specific resistor, capacitor, etc. goes bad in the control behind the button?

Oh, and taking the front center console off really helps with getting the HVAC controls replaced, I would recommend doing this.

wssix99

iTrader: (5)

The circuit is protected by a Circuit Breaker (not a relay) and some people replace that with a fuse. The Circuit Breaker is shared with the power seats and wears out over time.

Your problem is probably, indeed, a Relay. The circuit on the HVAC panel should have a relay, an integrated circuit, (microchip) and probalby a few resistors and/or capacitors. (I haven't looked at one in real life, but that's what the car's schematic implies.) I expect that relay is burning out on you. (I would be surprised if the other components are burning out.) If it is the relay, you should be able to match it up at a place like Mouser and solder a new one in. (Before you buy a new one, you should be able to test the relay with any 12V battery/source.)