Rear Window Defroster/defogger

My rear window defogger, blew off my window last night again and i think it's over drawing power. I could smell plastic burning before it blew, since i had a feeling that was the culprit, i turned to look at the back window, when i heard the sizzle and saw it pop with sparks flying. when i touched the connector it was extremely hot and the plastic outside was a little soft from being so hot. How would i test it to see if it's over drawing power? ( i do have tinted windows so it will be hard for me to test the entire grid) Where are the relays located? I know where the fuse is and mini relay, but are there any others that i should know of.

Grfnkl:

Did you do the tint yourself? Did you happen to do any other repairs to the defogger grid? I used to install after market defoggers and when we installed the grid on the window we had to more or less section off the grid to make sure it would not over heat.
I ask about the tint because if you put tint film over the grid you may be trapping too much of the heat causing the system to then overheat. I have installed a defogger and had it over heat on the very first test, often it would melt down the supply wire from the relay under the dash to the rear window.
I am looking thru the Haynes manual, it says to check the defogger you can use a volt meter and you can check each element at the centerr of the window if it reads 6v that element is OK if it reads 12v there is a break from the positive side and the center of the element. If it reads 0v then there is a break between center and the negative side. unfortunately there is nothing about relay location or testing the relay.
One thing that comes to mind after reading the testing instructions is: did something up on the rear shelf scratch the window on the positive side of the grid breaking the elements causing an excessive draw? Something to think about.
I can tell you that you are lucky that you saw what was giong on, a guy I used to work with once had his back window blow out from the over heating of the defogger. Glass everywhere, couldn't have happened to a nicer guy, (man what an assh***), I'm sorry but I laughed my ass off this guy deserved it.
Any way I hope this helps if you want I can try to scan the entire text on the rear window defogger testing and repair from the book and e-mail it to you, just let me know,

I hope this helps,
Dan

I read the Haynes manual as well, about testing it, just wanted to make sure that was the only way. The tint was professionally done back in 2002 for the entire window (one piece tint), never had any problem before this. I think the connection may have gotten distrubed after my accident, since I think they had to remove my back window in order to replace the back quarter panel. I'm gonna check a little closer to the connections on both sides and see if i can see something being scratched. I know it runs extremely hot since it will evaporate water off the window in pouring rain, all you will see is steam... so i think it;s a bit excessive. It was never that hot before. Thanks dan, I'll check into this a little deeper now...

In addition to the defogger relay and fuse there is a black box module called an RF filter located behind the rear right passenger side quarter panel/c-pillar trim. The signal to the rear defogger grid passes through the module as do radio antenna signals. I believe that GM has a TSB out on this for Grand Am and Aleros. The smell of plastic could be the module frying or it is shorted out. Maybe it or the cabling got damaged if it was on the same side of the accident damage.

Thanks for the info Bnaylor, The side the keeps disconnecting and burning plastic is that back corner as well. I'll have to take off the c-pillar cover and check it out. The accident was on the driver side, but Since the car was fixed i blew a rear speaker and now this... so I'm thinking it maybe all inter-related., If GM has A TSB out on this will they replace it for free? or does it have to be an official recall for them to do this... if not i'll attempt it myself first....

Thanks for the info Bnaylor, The side the keeps disconnecting and burning plastic is that back corner as well. I'll have to take off the c-pillar cover and check it out. The accident was on the driver side, but Since the car was fixed i blew a rear speaker and now this... so I'm thinking it maybe all inter-related., If GM has A TSB out on this will they replace it for free? or does it have to be an official recall for them to do this... if not i'll attempt it myself first....

You are welcome. One of the other symptoms was excessive radio static with or without the defogger turned on. The best thing to do is check with your local Pontiac dealer. Normally, although a TSB is out for a certain problem they will only replace/repair for free only if the car is still under a bumper to bumper warranty or if you have extended warranty it must be a covered item under the plan. Most of us are out of any warranty and just DIY. The hardest part is getting the trim off so the module can be accessed. Good luck!

Grfnkl, if you start pulling stuff apart you may want to check the wiring running back to the defogger, if the repairs were done on that side of the car the body shop may have pinched or cut a wire or two.

Hope you get it resolved.

For safety reasons you should get it resolved as soon as possible. 99% of the wiring going back to the defogger grid is covered so inspection will be necessary and that means removing trim, etc. Here are some links from the Alero forum applicable to the Grand Am where people had a similar problem and how the issue was resolved.

http://www.automotiveforums.com/vbulletin/showthread.php?t=176997&highlight=defogger

http://www.automotiveforums.com/vbulletin/showthread.php?t=485496&highlight=defogger

Last night i did pull off the C-pillar, rear door sill and carpet from the trunk, without locating the rf module. Although i was kind of rushing through this since it was bitter cold out with the wind blowing between the houses and cars, made it pretty cold out. I have to find a garage i can put the car in to shelter it from the cold so i can find it. Hopefully i can get to it by the end of the week. thanks for the links they are helpful, they even have the part numbers!!!!