No Rear Defrost

Lookwuticando · Post by **Lookwuticando** » January 1st, 2007, 7:37 pm

Well it's getting colder weather now and when my rear glass ices up I can't see squat back there....

I've tested the wires to the rear d-frost button and there's no power at the plug, hence the button won't light when pressed and nothing happens.

I've also got no power to the LED that comes on when the A/C button is pressed, although it does kick on the system. So I'm thinking the two are likely related.

Anybody have a prob like this before? If so, where was the trouble spot located?

mitmaks · Post by **mitmaks** » January 1st, 2007, 8:41 pm

most likely your fuse blew out

Lookwuticando · Post by **Lookwuticando** » January 1st, 2007, 9:05 pm

Wish it were that simple, I've checked all the fuses...

Bling Bling · Post by **Bling Bling** » January 1st, 2007, 9:41 pm

I had the same problem. Found that the metal piece that is soldered to the window defrost had actually come off. May want to look at that.

XL200 · Post by **XL200** » January 4th, 2007, 2:47 am

me too! my rear defrost metal tab connection is on just fine and all my fuses are good but no power running thru rear defrost wire. the defrost button light dosent come on so maybe a broken switch?? Ive checked everything else i can think of

Post by **Custommx3** » January 4th, 2007, 2:49 pm

I believe there is a circuit breaker by your fusebox (if I remember correctly) its a round button.

Imn ot 100% sure. I will speak to Jeff and have him scan the rear defrost info and put it in the online shop manual.

Lookwuticando · Post by **Lookwuticando** » January 4th, 2007, 4:44 pm

Man that'd really help out...I've got a Chilton manual but it's not very specific on this.

I think I've pinpointed at least part of my problem: When I took out my radio to put a CD deck there's a little red wire and a red w/black stripe wire that go to the rear defroster switch on the dash. They are bundled together with all the power and speaker wires etc. to the stereo, where there used to be a harness plug, and since I am running new speaker wire to the doors I cut them all and taped em up out of the way...oops...but now I can't remember how they hook back up

illapino · Post by **illapino** » January 4th, 2007, 5:30 pm

my rear defroster works, except at only like 4 of those "lines" ... so it only melts away a quarter of the fog ... what gives?

Lookwuticando · Post by **Lookwuticando** » January 4th, 2007, 6:35 pm

Probly got 4 good lines, the rest cut or broken some place

illapino · Post by **illapino** » January 5th, 2007, 2:28 am

well great. coz all the lines look identical to me ... i don't see anything cut or broken ... and the lines that do work aren't necessarily right next to each other. there's a few running across the center of the rear windshield that work, and then there's more near the bottom that work (which is fortunate in that location since it allows me to see at least some of the cars behind me)

Tempus · Post by **Tempus** » January 5th, 2007, 2:05 pm

the defroster is basically a resistance heater.. Electrical current flowing through the 'wires' causes them to heat up. In most cases the wires are actually conductive paint that's silkscreened on to the inside of the glass. Any tiny break in those painted 'wires' will cause a break in the circuit and thus that 'wire' won't heat up.

we are talking any fine scratch or hairline crack, it doesn't need to be much to cause a fault. If it's not heating there HAS to be some break in the circuit.

You can get conductive paint that can be used to repair the breaks.. So get some of that at an autoparts store, and then go over those 'wires' with a magnifying glass if need be until you find the break. the follow directions on the paint to repair it.

mx3optidrive · Post by **mx3optidrive** » January 7th, 2007, 10:32 am

Someone should make this a Sticky. Seem to come up a couple of times each winter. These are a couple of quotes from posts that I answered in the past about this same subject. Sorry for the long post, but I wanted to make sure I didn't miss anything.

Hey people, I had the same problem. The light was out and I could hear the relay clicking and yesturday, just for curiousity, I took out the relay which I located by following the clicking sound and unpluged it. Guess what, it was burnt out and the plug was even burnt. So I would check the relay even if it is clicking because it may still be bad like mine. I hope this helps.<P>Jeff

The relay is under the dash on the driver's side almost directly in front of the fuse box. I think that there are 3 or 4 relays in a row, not attached to each other and to remove it all you have to do is pull down hard. The relay is, I think, the 2nd back from the firewall just listen for the clicking if it still is clicking. Hope this helps .

If you push the button in and hear the relay clicking then all you have to do is follow the previous instructions and you can find the right relay by placing your hand or fingerson each relay while pushing the button and you should be able to feel the relay latching.<p>If you do not hear the relay latching then you could also take it to a Mazda dealer and they should be able to show you or tell you where it is in greater detail.
Good luck guys

What usually happens is that Salt (from winter driving) or water gets into the relay connections and corrodes the connections which causes more resistance inside the relay or shorts it our internally and causes it to melt.

The relay does make a "click" noise when press the defrost buttom. So i think it is the right one. The relay has this info on it.

H270 (big letters)
DC12V20A
IMASEN
2G18

My relay was still clicking and I changed it anyway and it worked ever since. My relay was faulty and when I unplugged it from the harness, I noticed that the harness itself was burnt and some of the wires were too so I had to change the harness as well. Chances are it is the relay, it is only like $3 to replace.

Just to let you know what caused my relay to short out, it was from the salt they use on the roads around here that got into the plug and shorted the relay out and burnt out the relay prematurely. The guys at Mazda said if I didn't catch it, it might have caused a fire. By the way the plug looked and the wires, I think they were right. Like I said earlier, the relay was clicking and I thought it was working fine until I changed it.

If your wires and/or plug are not burnt or damaged, all you have to do is unplug the old relay and plug in the new one. If it is damaged, you have to make up new ends for the wires and plug them into the right poles on the relay.

Good luck man. I hate the Canadian winter and that is why I store my car now. Let me know if this helps.

Jeff

Lookwuticando · Post by **Lookwuticando** » January 7th, 2007, 12:51 pm

Hey nice work. True, this does seem like a fairly common problem around here. My car spent some time in Ohio before I got it, which lead me to have to replace my exhaust pipe underneath that had big rust holes in it, so that's always a possibility...glad the relays are easy to get to and not buried in the dash like on a lot of cars. I know one thing, I still have to figure out the two red wires I was talking about....any luck with getting that part of the online manual up?