Rear Wimndow Defrost not working

[JochenWoern]

Well, I guess I am starting to realize HOW LUCKY I am to be living in Northen CA. The last week we had overnight tempartures in the 20's, which is pretty darn cold for around here.

-----> Yes, I realize that this is not cold to the rest of the country on the East Coast.

Never the less, ever since it is cold there are all kinds of things happening to the truck. Noticed some leaky oil or tranny cooler lines, rear heater is acting up again after I just changed the Blend Door in July, as it was only blowing hot air. Fixed it and the air was blowing cold, now the heater does no longer want to work and it is blowing cool air in the back. I am thinking I might have to check all my actuators as I believe these no longer properly open and close for the set temperature anymore.

Ok, but now to the Rear Deforst. When I hit the button on the dash, the light on the knob comes on and I also hear the relay "click", but it does not appear that the rear window is getting heated.

Any thoughts?

Thanks for the help guys.

 

[BirchyBoy]

I'm not familiar with the NBS, but the OBS has "rods" that make contact between the body and the rear door when it's open. These "rods" lose conductivity and need to be cleaned with emory cloth or light sandpaper.

 

[JochenWoern]

I'm not familiar with the NBS, but the OBS has "rods" that make contact between the body and the rear door when it's open. These "rods" lose conductivity and need to be cleaned with emory cloth or light sandpaper.

There are two connectors at the rear window that plug into the wire coming from the ceiling.
Are you suggesting that I unplug these connectors and clean the tabs that are connected to the rear window heater, then re-connect?

 

[BirchyBoy]

There are two connectors at the rear window that plug into the wire coming from the ceiling.
Are you suggesting that I unplug these connectors and clean the tabs that are connected to the rear window heater, then re-connect?

No sorry. The OBS (barn door model) has pins that make contact when the doors are closed. Yours must be different than this.

Sorry for the confusion.

 

[JochenWoern]

No sorry. The OBS (barn door model) has pins that make contact when the doors are closed. Yours must be different than this.

Sorry for the confusion.

YES. I rememeber that when I had my '99 Tahoe.

BEST TRUCK EVER overall, should have never gotten rid of it and should have drove it to the ground.

AND, it did not have all these electronic gadgets like the Auto Climate Control which never wants to work.

 

[Yukongk]

Wish I could be of more help, but I remember seeing a thread about this and IIRC the wiring for this and the OP's rear wiper had a bad ground. Hopefully, someone can chime in.

 

[Rivieraracing]

Are your side mirrors defrosting when you push the button? And you say knob, do you mean the right most button on the climate control?

 

[JochenWoern]

Are your side mirrors defrosting when you push the button? And you say knob, do you mean the right most button on the climate control?

Yes on both Chris.

Sorry, the German said knob, but meant button. After 25 years I still do not speak it fluent. ;-)

 

[Rivieraracing]

Yes on both Chris.

Sorry, the German said knob, but meant button. After 25 years I still do not speak it fluent. ;-)

No biggie, was just making sure that the right stuff was being turned on which I figured it was! Might not be a bad idea to check for voltage at the rear window to see if you are even getting juice at the window when the button is pressed!

 

[JochenWoern]

No biggie, was just making sure that the right stuff was being turned on which I figured it was! Might not be a bad idea to check for voltage at the rear window to see if you are even getting juice at the window when the button is pressed!

So what if there is no juice? Then what? Since the mirrors defrost, the button obviously works.

 

[Rivieraracing]

So what if there is no juice? Then what? Since the mirrors defrost, the button obviously works.

Good question, obviously with the mirrors working then it's not a fuse problem. If that was the case, then you would have to go from the plug on the rear window and work your way back till you found the problem checking for voltage and/or bad wires/connections.

 

[JochenWoern]

Good question, obviously with the mirrors working then it's not a fuse problem. If that was the case, then you would have to go from the plug on the rear window and work your way back till you found the problem checking for voltage and/or bad wires/connections.

I guess I will check the connectors to the left and right of the window first, maybe the tabs connected with the defrost wire are corroded and do not make connection?

 

[Rivieraracing]

Had some free time tonight so I went out to our truck to check voltage of mine since it works great! Just remember, mines a 2002 so it might be different than yours but it should still have voltage at the tabs on the window with at least the window closed (yours might shut off power to it like it does to the rear window wiper to keep it from running while the window is open!)

So with my rear defrost switch on I was getting 10.4v at the passenger side power plug on the window and the drivers side I was getting .9v. Didn't matter if the window was open or not (which surprised me). I used the tie downs in the back as my ground (might take a bit of scratching around on the bolt head to make a good ground contact but it did work) and obviously used the positive end on the tabs on the window.

Let me know what you come up with!

 

[shadoow98]

Hi I had the same problem I would hear the "click" but no heat at all. What I found out for my problem and I don't know if it would work also for you but it was the rear window not getting a good negative connection.

Here is my post with my fix
http://www.tahoeyukonforum.com/forum/showthread.php?t=56248

Its just running a wire from a metal part of the rear door to the driver side pin of the window defroster.

 

[JochenWoern]

Had some free time tonight so I went out to our truck to check voltage of mine since it works great! Just remember, mines a 2002 so it might be different than yours but it should still have voltage at the tabs on the window with at least the window closed (yours might shut off power to it like it does to the rear window wiper to keep it from running while the window is open!)

So with my rear defrost switch on I was getting 10.4v at the passenger side power plug on the window and the drivers side I was getting .9v. Didn't matter if the window was open or not (which surprised me). I used the tie downs in the back as my ground (might take a bit of scratching around on the bolt head to make a good ground contact but it did work) and obviously used the positive end on the tabs on the window.

Let me know what you come up with!

So, finally got around to measure and had approx. the same voltages as above and determined that there is no voltage problem.

Guess the only issue now could be that there is a break in the heater wire accross the back window?

 

[Rivieraracing]

Well it may not seem like it but consider that a blessing because now you know it's a problem at the glass instead of having to do additional investigating and diagnosing! If I get a chance tomorrow, I'll unhook both wires going to the glass and see what I get for ohms between (if that even matters at all) and see if they compare!

Thanks again for the seat heater diagram that you emailed me, I need to make some time and get my seat figured out before its too late and warm out!

 

[JochenWoern]

Well it may not seem like it but consider that a blessing because now you know it's a problem at the glass instead of having to do additional investigating and diagnosing! If I get a chance tomorrow, I'll unhook both wires going to the glass and see what I get for ohms between (if that even matters at all) and see if they compare!

Thanks again for the seat heater diagram that you emailed me, I need to make some time and get my seat figured out before its too late and warm out!

Your welcome Chris, my pleasure.

 

[TheSwede]

I had my rear glass blewn out yesterday......it was on the yard not driven in several hours . +15-20 C. I'm thinking i had some kind of a short on the passanger side. So i hope My dealer can find out what went wrong when they replace the glass.

 

[joltman]

So, I've discovered my rear window is not defrosting. I've never heard a click when I press the defrost button. And it hasn't been cold enough for the side mirrors to get iced, so I have no idea if the button works at all.

Looks like I need to compare both wires to the window for voltage. I should ground to the truck and not but the voltage meter between the two wires?

Would you be able to see a bad heating wire on the glass? Thanks for the help (and sorry to hijack the thread!!)

 

[Justinj360]

Did you ever check your rear defrost fuse under the hood? Your problem sounds exactly how mine is when it's blown. It goes out often. Not sure why