Burnt Smell From Heater/AC Ducts

Hello, for the last week I have been getting a burnt electrical smell from my heat/AC ducts after the truck sits for several hours. It does this for about 15-30 seconds and then dissipates. It does this even with the engine off and just the blower motor going. If the blower is off I can't smell anything. I have tried changing the resistor and the blower motor so that doesn't seem to be it. The old ones worked fine and didn't smell. The heater core is only 2 years old and it doesn't smell like antifreeze either. I also don't see any leaks on the passenger floor. The smell seems worse on the driver's side than the passenger side. I have owned the truck for over 10 years and have never experienced this, now it does it every day.

 

Inspect the wiring specifically connections at the ignition switch, blower motor, and resistor. An IR temp gun may show a hot spot if a visual inspection for a melted or corroded connector doesn't find any.

 

I had the fan out, the resistor out (again), the radio out, the instrument cluster out and still nothing. But the trans let go so now I'm dead in the water with that as it's out for repair. Some people have said to pull the heater core but so far it doesn't leak and the smell goes away after about 30 seconds (truck running or not with the fan on). I wonder if it could be the temperature sensor in the evaporator core?

 

Please check the electric part of the ignition switch, especially the big white connector on the LEFT side of the steering column. Disconnect and inspect. Mine melted down a couple years ago because the full current of the heater fan runs through it.

 

The ignition switch seems fine. The smell only comes from the heat/AC ducts. Still no obvious leaks from the heater core and the AC still works OK. I don't really want to pull the whole dash and heat box assembly unless I really have to. I would think if it was the heater core that I would get a smell all the time.

 

If you're sure its an electrical smell, check the blower motor and resistor.

Look under the dash behind the glove box where the recirc intake is. Maybe some other component or wire not related to the HVAC system is creating the smell and the blower is just distributing it.

 

I will have look where that recirc intake is. Thanks.