UGH. While I was warming up the truck to adjust the VOTM idle speed, a light wispy smoke (!) started to emit from the defroster vent. I shut off the motor and removed the key in fear/disgust.

FYI it's a 1982 F150 XLT Lariat with all the factory options. It continued to smoke like that for at least a couple minutes before it subsided.

While it was running, the only controls I touched other than the ignition switch were the headlights and the windshield wiper and washer. I tried the instrument dimmer and dome light with the lights on, and attempted to make the washer operate while the wipers did their thing.

I know this is a stab in the dark, but any of you out there have an issue that arose like this? I know it's electrical but short of ripping the whole dash out I'm wondering exactly what electronics reside in the center of the dash that could make this happen.

 

The most likely cause of the smoke is leaves or pine needles in the heater duct, up against the resistor pack for the fan motor:

Heating, Ventilation, & Air Conditioning - ???Gary's Garagemahal

Page 83, figure 1 shows the location. If you remove the fan motor, you'll have pretty good access to clean out the crud.

 

I had a bad heater core do that to me last year. Much more than a light, wisp. Scared the carps out of me thinking it was a flare up in the dash venting thru the defrost slots.

 

Autocorrect much?

I just threw that out there for the halibut.

 

I like your answer a lot. And it makes good sense too, considering the truck has been sitting idle for a few years

 

Did it actually smell like smoke?

The reason I ask is that a coolant (ethylene glycol) leak at the heater core produces a thick white fog, that looks like smoke, up through the vents.......I had an '88 which did this.

 

That would be my question also.

Coolant leak will smell sweet.
Leaves and crap (or carp?) would smell like leaves burning.
Wires burning up smells more like plastic burning.

I would think coolant & leaves would come out the vents, burnt wires from everywhere.
Also if the heater core is leaking bad/long enough the windows fog up and cant wipe off and the floor on the passenger side can be wet.

So what did it smell like?
Dave ----

 

You guys have it covered, either burning leaves from the cowl, or heater core leak, are the to most common sources of this.......

 

Definitely not coolant - know that smell well. It was a smell that was hard to call out. Could have been a burnt wire smell, could not have. It was 115 degrees here yesterday one would think that could contribute to the problem.

 

Ambient temperature shouldn't matter.

Yes, figure out if the smell is electrical, oil, leaves, plastic, whatever... I would first be looking in the heater box at that fan switch....

 

Pull the resistor pack from the HVAC and see if it looks like this one. (Photo credit to Hardward.)

 

And, if that is what you find, then proceed to removing the blower fan and reach both ways into the duct and clean. It helps to use a shop vac.

 

A fair number of 60s and 70s trucks have been total loss due to fire, from crap in the heater blower. Any Ford that has been sitting outside for a long time especially, should be checked out.

 

I was able to pull the fan motor pretty easily on my 84, with A/C, and clean a bunch of debris out of the heater housing.
Scary feeling, going down the road, and to keep smelling burning leaves, and then have the cab fill with smoke.....

 

Yup. Same experience.