I had the defrost on this morning because the back window had dew all over it. About ten minutes down the road on the way to work (cut the defroster off about a minute before) and I hear a loud pop. I thought the car had backfired. I look in my rear view and the glass looked like it was froze up. Put two and two together and realized the glass had shattered. I smelt something burning right after I left my house but I thought it was another car in front of me (guess it was me). It was a nice start to my morning. Anyone else ever heard of this happening?

 

Nope never heard of it, was the window hot? Maybe the defroster stayed on or something.

 

sounds like it shorted out and kept heating to much

 

This is my guess too. Some sort of short probably caused heat in a concentrated area.

 

I would have thought it would have popped a fuse or something if it shorted out. It was probably 68 or so this morning and the sun was just starting to rise. I've forgot to cut the defroster off before and it ran the whole 20-25 minutes to work, whereas this time it only ran for ten minutes or so. I didn't touch the window after it happened or anything to see if it was super hot. I was worried the sh*t was going to fall in. I think my tint saved it from being a lot worse. Now I'm just worried about it happeining again when I get it replaced.

 

If i remember right, it turns itself off at a certain temp. So it definitely failed somehow.

 

Its laminated glass so it wasnt going anywhere.

 

I'm not so sure, I had a couple quarter size pieces fall out when I shut my door.

 

Rear glass is not laminated, tempered only and even leaving the defrost on in the summer should not do that. The grids create their own resistance as they heat up. Any chance a rock from somewhere hit it? Drive under an overpass?

 

I guess it's a possiblilty that a rock hit it as I did drive under an overpass about a mile before it happened. I did smell something burning before it happened but how could it get that hot without popping a fuse? I'm not 100% sure that the smell was from my car, could've been someone up the road in front of me.

 

Whenever I get a chance I'll have to upload some pics. It looks like it came from the defroster pad area on the glass since that has the most damage. I'm just worried about it happening again after getting the glass replace which will hopefully be tomorrow.

 

It can only get so warm and not enough to break the glass. As the grid heats up its resistance goes up and the current flow drops. The grid is operated from a relay and it's probably a 30 amp relay. I am sure it was something else.

 

Could cold water have dropped on it? My MIL has shattered a windshield washing it from that.

 

Defroster has a connection like this on each side. Looks like all the strands run parallel from one side to the other.

Did you have anything conductive rubbing up against your back window? It looks like the strands run parallel to each other so you couldn't short strand to strand. Possible though something conductive could short a strand to ground. Though when I looked in the back of my car I couldn't see any bare metal. If it didn't short I wonder what the burning smell was.

 

Nothing back there to short. I'm not sure if the burning was me or not. The wires looked fine but I didn't want to mess with it too much and have a bunch of little pieces of glass fall down. I'll take a closer look after it gets replaced.

 

Pics

 

It was in the upper 60s. I can't imagine anything that cold out that could have done it.

 

Take a close up of the drivers side by the hole looks like something is burnt there

 

Wow, never heard of that happening before. It's possible a dead short caused the pop you heard, can you also take a pic of the connection to the rear window from inside the car.
I wonder if the burning smell was insulation breakdown or an external contamination that burnt up and caused a short.

 

It could have been cold air going through the heated glass? Last winter i had my front windshield crack after i turned off my defrost the same way you did. I had it on, it was raining and was like 40*. I stayed in the parking lot getting warm (here in texas below 60* is freezing temps lol) and drove off forget to turn It off. Down the highway i turned it off and heard a crack, my windshield was cracked on the bottom right where the defrost air was hittng it. It was 3am and no one but me on the highway so it was not a rock. So i do believe it might have been the defrost heat in combination with the cold air.

 

Think you may just be seeing where the defroster tab seperated from the pad on the windshield. I'll try to get another pic tonight when I get off work.

 

It does seem to me that the cracks seem to be originating from that tab tho, seeing the way they radiate from it compared to the tab on the other side. How's the fuse for the defroster?

 

That's my thought too. I'll check the fuse. In my mind if something had hit it I would have heard 2 different noises, not just one pop.

 

I had a back glass explode from something hitting it. The shattering of the tempered glass is all you hear.
Your new window comes with the grid and everything all in place. You won't have an issue after it is installed.

The glass is tempered at 1150F and can operate in temps to 450F. Mine was over 150 yesterday in the direct sun and I turned on the Rear window defogger with a jumper in the BEC and let it heat up while I was staining some wood. Nothing happened. Our front and rear glass does not use trim either so all it takes is a pebble to wedge in-between the metal and glass to cause pressure when it starts warming up.

 

I think I do have a short in the wiring (which would explain the burning smell). I checked my new glass after it was installed with an infared temperature gun (like you HGT) and within a couple of minutes of the defrost being on it was reading 180 degress at the pads. I could barely put my hand up to it. If I took it off the pad and checked a spot around it the temp was around 85. I did it around 745 last night so it wasn't during the middle of the day in the heat. I also had my car turned away from the sun as it was going down. I guess now I will be searching for the short.

Also, the glass I got was used and the people that installed it came out to my house (I wasn't there). The rubber moulding that's under the glass has holes and tears all in it. Needless to say I'm not happy. This is the fourth glass I've had this place put in and I never had a problem before. They actually replaced my rear glass a couple of months ago because the defroster tab kept coming off (despite me trying to solder it back on). That one looked fine, this one not so much.