Hot/burning wax/plastic smell from vents on startup

[Jeff d]

I've now owned my '03 Yukon XL for about 5 months and about 1/2 the time when I start it up with the blower on it smells like hot wax for a few seconds. It's almost a burning smell but not quite. Kinda like plastic that's been heated enough to soften but not actually melt or catch fire.

This smell is immediate. The first puffs of air that blow out of the vents smell like this and then it's immediately gone. More often than not it's on the first start of the day on a stone cold engine. It usually does not occur on restarts between short trips and I've never smelled it after startup in the last 6,000 miles or so (since I've owned it).

I'm pretty sure it does it whether the AC itself is on or off (i.e. just the fan is on) but I need to do some more experimenting with this. I've searched a bit but haven't come up with anything that matches my description.

Any idea what could cause this?

---------- Post added at 03:35 PM ---------- Previous post was at 03:11 PM ----------

I got less specific with my searching (i.e. GMC and Chevy instead of Yukon and Tahoe) and found some posts suggesting that the Blower Motor Resistor is a common source of this kind of smell. I'm going to continue searching but does anyone know if this would be the correct part:
http://www.amazon.com/ACDelco-15-81087-Blower-Motor-Resistor/dp/B000NW4O8E

If so where would I find that behind the dash?

 

[MurdrNali]

I was about to say my money is on the blower motor resistor and then I read your edit lol had the same issue with my last truck (05 Sierra) and the resistor was under the dash, passenger side kinda below/behind the glove compartment. That's a pretty good deal on that too considering I bought mine at a dealer at employee pricing and it was around 70-80 bucks IIRC. Mine was melted to shit when I removed it. I'm surprised it never caught fire.

 

[Jeff d]

I found the tsb/10 year warranty coverage for this issue. Unfortunately my vehicle was purchased in April of 2003. So, it just expired. Oh well, $50 is right at the point where I would have debated whether it was even worth pursuing through a dealer vs. just swapping in the part myself. I'll probably just order it off amazon, swap it out, inspect the harness and hope for the best.

I found a YouTube video that shows how to remove/replace the resistor. Seems simple enough.

 

[Jeff d]

The AC Delco part I linked in my first post is apparently not the right one. 15-81086 is supposedly the correct one for my particular vehicle:
http://www.amazon.com/ACDelco-15-81086-Auxiliary-Blower-Resistor/dp/B000NW6WE8

I'm considering just buying the Dorman equivalent though. It's cheaper, has positive reviews and GM obviously didn't get it right on the original design so why should I give them another shot?
http://www.amazon.com/Dorman-973-009-Resistor-Cadillac-Chevrolet/dp/B003YLH8ZW

I'll probably pull the cover off first and see if I need the harness too or not. If so I will certainly go Dorman there because it's a lot cheaper and has positive reviews. It's even got a legit Delphi connector on it if those pictures are accurate:
http://www.amazon.com/Dorman-645-702-Blower-Resistor-Connector/dp/B0052XHBO8

 

[Jeff d]

So I pulled what I thought would be the resistor and it was actually a completely different piece than what I expected. Based on a quick search it appears to be a "Control Module":
http://www.amazon.com/ACDelco-15-80567-Control-Module-Kit/dp/B0016IMSB4

I saw/smelled no evidence of burning on the Control Module.

Is this instead of a blower motor resistor? Possibly for vehicles with dual zone controls? Or am I looking in the wrong place?

 

[Jeff d]

So I pulled what I thought would be the resistor and it was actually a completely different piece than what I expected. Based on a quick search it appears to be a "Control Module":
http://www.amazon.com/ACDelco-15-80567-Control-Module-Kit/dp/B0016IMSB4

I saw/smelled no evidence of burning on the Control Module.

Is this instead of a blower motor resistor? Possibly for vehicles with dual zone controls? Or am I looking in the wrong place?

I haven't been on the forums in a while but FWIW I ordered the "ACDelco 15-80567 Control Module Kit" I mentioned above, swapped it in and it resolved the issue. My blower speed is consistent now (When not on "Auto") and the smell is gone. It was not "plug and play" though. The plug on the factory harness is different than the revised part so a new pigtail is included. You cut three wires and then attach the new pigtail (The wire colors are the same) to the same wires. It was no big deal but I expected plug and play.