I've had this truck for about a month ('85 F-250 Explorer 460 4x4), but on the way to work yesterday, I decided to try out the A/C for the first time.

Not sure why I didn't check it when I was test driving the rig, I (correctly) assumed A/C on a 28 year old truck surely wouldn't work.

Turned it to A/C Max and fan speed to high. Soon after, I start smelling smoke, but it wasn't strong at first and smelled kind of "stale" (if there's a such thing as stale smoke). I left it on, thinking that it was some junk or crap in the vents that needed to get aired out.

Very quickly, the smell got STRONG and smoke started POURING out of the vents. I turned the A/C off and proceeded to keep driving, hoping for the best, but it soon got so bad I couldn't breathe, and I half-expected to see flames in very short order. I stopped it and shut it down right in the middle of the road (didn't want to get too close to grass & such on the side of the road, because of the fire danger here) and got the heck out.

The smoke gradually dissipated over the next 5 minutes or so, and I did not hear or see a fire or anything unusual. I got back in it, and though it (and I) now smelled like a campfire, I proceeded to complete my drive to work, which the truck did beautifully.

I'm at a loss to explain what happened, and I surely don't want to mess with the A/C or fan now... Where should I go looking for the cause? How do I rip into the HVAC system to see what happened?

 

The fan speeds are controlled by a resistor network mounted IN the ductwork. They do that to keep the resistors cool by them being mounted in the airflow of the fan. Problem is the ductwork gets full of leaves and junk, and then when you turn the blower on and the resistors get hot, they catch leaves and trash on fire inside the ductwork.

The resistors look like a plug with several wires going into the ductwork on the engine side. Unplug the plug, and then unbolt the assembly and you can take the resistors out. You can also pull the fan blower, and try to reach down in there and clean out some of the debris from inside.

 

The same thing happened to me last year. I just left Pick-n-Pull in north St. Louis. Less then a mile down the road and smoke starts pouring out of the vents. I pulled into a vacant lot (not hard to find), popped the hood and unplugged the wires running to the fan resistor then let the fan run on high to disipate the smoke. (This may have been bad, I guess it could have fed the fire extra oxygen) I had a fire extinguisher in the cab just in case. Luckily the smoke faded away and I returned home. I cleaned out all the leaves in the vents and plugged the resistor back in. I guess it was fried, only high works now.

It took over a month for the burnt smell to leave the cab. Talk about ruining a day.

 

in the 14 years i've own my 1985 F250, it has caught fire 11 times.. of those 11 times 8 were electrical and 3 my fault...

I've taken to having a few gallons of water with me at all times, not only for the cooling system but to put out any fires that may break out

 

The Pick & Pull on Hall Street; yes no shortage of empty lots over there! I just moved here from St. Charles this year, I've been to that junkyard many 'o times.

Glad to hear this is not an isolated incident. I will definitely check for and remove any crap down there, thought it may be all ashes by now. I did notice an abundance of pine needles near and inside the vents by the windshield wipers, when I bought the truck. I suspect it was pine needles catching on fire.

Will take the idea of carrying a fire extinguisher with me seriously!

 

Get rid of the water and get an ABC rated fire extinguisher that'll handle fuel/grease/oil based fires and electrical fires.

Water is good, but it's not that good.

I've got an ABC fire extinguisher in my truck, just have to install the mounting bracket to get it off the floor behind my seat.

I stand by what I say when I say that everyone needs 1) a set of quality jumper cables, 2) a good non-factory jack setup (floor jack) that will allow you to easily jack up a vehicle regardless of it's an emergency or not, 3) an ABC rated fire extinguisher, 4) a bicycle pump, 5) a tire plug kit with extra plugs and a bottle of water and a bottle of dawn dish soap, 6) and a good spare tire that's rotated with your other 4 wheels at regular intervals.

If you don't have any of the above with you in your vehicle at all times, you need to! Consider this the basic emergency kit.

 

This is all great info - and quakerj, good on ya for having the presence of mind on where to stop. I repped you for that!