Rear Defrost sucks all of a sudden

[mikeinaus]

hey everyone. ive noticed in the past few weeks that my rear defrost has become almost useless. on my way to work every morning i have a bunch of dew covering the back windshield. if i turn the rear defrost on it barely works. after 10min or so its heated up enough to clear just the lines threw the moisture but it hasnt been able to completely clear it for a few weeks now. i know its changed because shortly before i noticed it getting bad, i said to myself "man my rear defrost works really well". now im saying "man its hard to parallel park when i cant see anything behind me". luckily it hasnt gotten cold enough to snow or make frost (for the most part). is there anything in particular i should be looking for, or do i most likely have a short on one of the heating elements?

[Ryan]

The most common thing ever is the relay plug burning up. Check under the dash for a burnt relay plug and report back. You should un clip it and check them all. To know exactly which one, check the manuals.

[mikeinaus]

bit of a dumb question but where are the relays under the dash? ive only known of the ones in the engine bay... are they near the fuses?

if it is in fact the relay is it a good idea to replace it with a 40amp one to match the main engine bay 40amp fuse? source http://forum.mx-3.com/phpBB3/viewtopic.php?f=38&t=67873

also wouldnt a bad relay make it not work at all? are relays not like fuses where once they blow they no longer complete the circuit?

[Newfie_dan]

a bad relay can make it work like crap if there is high resistance internally in the relay, high resistance makes for low current, the relays are right up under the dash drivers side right towards the firewall area, its easy to see if you get under there with a light.

[mikeinaus]

thanks Dan. i have a look at it tomorrow. in reguards to that other thread there wouldnt be any negative effects of using a 40amp fuse over the stock 20amp would there?

[Ryan]

If by fuse you mean relay, yeah it should help it from burning again.

[mikeinaus]

yeah thats the one... any idea what a good price for these are? i just called my local auto store and they said $25 after my discount, and could only get the stock 20amp. ive seen ones on ebay for like $4 but im not sure if they have the proper pin count/layout.

temporary fix. plugged my defrost into a different relay that controlls the cluster lights, door beep (and possibly other things?) and it worked fine. since my defrost relay is technically working, it just isnt suppling enough voltage or something, i just swapped the defrost and cluster relays. they are both rated at 12v and 20amp so im thinking ill be fine until the relay finally craps out.

[Nd4SpdSe]

Can you use a regular relay or does it have a special connection?

You can get 30amp automotive relays at The Source (aka Radio Shack) and Canadian Tire, they run for $11-$15 Canadian, It's not 40amp, but it's better than 20A. What's weird, I remember them listing relays exactly as "30/40" amp, kinda odd.

Here's a website, they list 40, 50 and 60amp relays:
http://www.wiringproducts.com/contents/ ... relay.html

That's just a quick Google search too

[mikeinaus]

the connection is 2 2 side by side 4 pin connection. i saw that website but doesnt look like they carry the proper ones. the source also looks like it carries the different connection aswell. guess ill just have to order that one from lordco...

[Newfie_dan]

If by fuse you mean relay, yeah it should help it from burning again.

yes that is what I meant, I fused the relay for the rear defrost on the constant power side to prevent the burning of that relay with a 20 amp inline fuse. The relays is socket specific so using a regular relay will not work unless you cut off the plug and wire it to a regular relay which is doable.

[Ryan]

Thats what I was talking about, soldering in a 40A connector/relay. A 20A inline fuse will continue to blow... doesn't really solve the problem.

[Newfie_dan]

Yeah the fuse was meant as a backup not a fix to prevent the relay from burning up, what I did was replace the relay with a better relay with higher current capability and cut the factory plug off and wired in the new one. I was paranoid about it so I just wired in the inline as a backup.