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Paul Wojcicki

2017 Sierra Denali rear window EXPLODED!!!

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.. just in case you thought this was just a GM problem.. nope, appears to be a sliding window with defrost problem.. seems like a pretty common failure on F150 as well (maybe more common)..

 

http://www.carproblemzoo.com/ford/f-150/rear-window-defogger-problems.php

 

...WOW nearly 130 documented F150 cases here

https://www.glassbytes.com/2013/12/several-ford-f-150-owners-report-shattering-back-lites-to-nhtsa/

 

.. link to file complaints for Canadian owners

https://wwwapps.tc.gc.ca/Saf-Sec-Sur/7/PCDB-BDPP/fc-cp.aspx?lang=eng

 

.. also found this interesting GM bulletin..

https://gm.oemdtc.com/1974/14815-heated-back-window-glass-structurally-weakened-due-to-surface-flaw-2015-chevrolet-silverado-gmc-sierra

Edited by STRMTRPR
added link

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Pulled the square 30A # 10 fuse from the under hood fuse box. 

 

The rear defroster button still lights up on remote start but rear window is cold 🥶  to touch. 👍

Edited by 2009GMC

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37 minutes ago, 2009GMC said:

Pulled the square 30A # 10 fuse from the under hood fuse box. 

 

The rear defroster button still lights up on remote start but rear window is cold 🥶  to touch. 👍

I’ve been think of pulling the fuse or relay also. Do the heated mirrors still work when the button is pushed?

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.. so I was thinking about this window problem as a short resulting in an increase in current flow..and the possibility of introducing some form of current limiting/monitoring to prevent overheating/melting/smoking

..BUT.. I haven't seen any reports of the fuse blowing - this is at its simplest the weak link in the circuit and basic overcurrent protection.. so why didn't it blow? let's assume the current flow never reached the 30A threshold at the time of failure.. what is the current draw under normal operation? I measured the current flow of my rear defog circuit today; and for the purpose of simplifying the hypothesis here it I'll round it off to: 18A at cold startup of 0C or 32F. Let's also assume that the circuit voltage is always constant.

..so if we are correct that the current draw never reached the peak 30A rating of the fuse where did all the heat/smoke come from? .. now this is going way back to my days in school but it then only makes sense that condition responsible is resistive heating (l2R).. increased resistance from poor contact of the middle sliding window.. think toaster oven, space heater etc.. this phenomenon causes thermal expansion and can literally melt wires.

 

.. Circuit design theory is not my area of expertise.. my background is Robotics.. so I'm hoping for members with expertise to chime in with thoughts.

 

.. If the window is indeed experiencing resistive heating from a high resistance connection due to poor/short sighted design what can be done as a preventive failsafe?.. add a cycling thermostat or thermal fuse like used in a clothes dryer?.. would be a rather ugly preventive measure to what is likely a design flaw with the window connection.. and seems unlikely that GM would step up and go the design route given what also seems to be a known problem with the Ford window design (same glass supplier??)

 

 

Edited by STRMTRPR
.. thoughts on dryer fuse

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On 3/15/2019 at 5:19 PM, Blue5.3l said:

I’ve been think of pulling the fuse or relay also. Do the heated mirrors still work when the button is pushed?

Yes I verified this morning that my mirrors were warm and my rear window was cold since I pulled the fuse.

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On 3/15/2019 at 8:19 PM, Blue5.3l said:

I’ve been think of pulling the fuse or relay also. Do the heated mirrors still work when the button is pushed?

Yes, just pull the fuse only. The relay controls both the mirrors and the rear defogger. 

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.. so I was thinking about this window problem as a short resulting in an increase in current flow..and the possibility of introducing some form of current limiting/monitoring to prevent overheating/melting/smoking
..BUT.. I haven't seen any reports of the fuse blowing - this is at its simplest the weak link in the circuit and basic overcurrent protection.. so why didn't it blow? let's assume the current flow never reached the 30A threshold at the time of failure.. what is the current draw under normal operation? I measured the current flow of my rear defog circuit today; and for the purpose of simplifying the hypothesis here it I'll round it off to: 18A at cold startup of 0C or 32F. Let's also assume that the circuit voltage is always constant.
..so if we are correct that the current draw never reached the peak 30A rating of the fuse where did all the heat/smoke come from? .. now this is going way back to my days in school but it then only makes sense that condition responsible is resistive heating (l2R).. increased resistance from poor contact of the middle sliding window.. think toaster oven, space heater etc.. this phenomenon causes thermal expansion and can literally melt wires.
 
.. Circuit design theory is not my area of expertise.. my background is Robotics.. so I'm hoping for members with expertise to chime in with thoughts.
 
.. If the window is indeed experiencing resistive heating from a high resistance connection due to poor/short sighted design what can be done as a preventive failsafe?.. add a cycling thermostat or thermal fuse like used in a clothes dryer?.. would be a rather ugly preventive measure to what is likely a design flaw with the window connection.. and seems unlikely that GM would step up and go the design route given what also seems to be a known problem with the Ford window design (same glass supplier??)
 
 
This kid is on to something. Many key works in there are spot on.
When and where the load is the highest is where you will have the hottest spot. And where the failure will occur. What can be done to reduce this and when what is the best amp rating of the circuit? Like all things the draw can be high then reduced after a second or so, think hid lights running super low amps but to start we have seen a need for up to 30amp fuses. So the difficulty is how do you protect that circuit.

Sent from my SM-N960U using Tapatalk

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