Blower motor only running on high...?
 

Hello,

1985 6.9 Regular Cab long bed F250 4x4 with C6 trans, Cruise and Air.

Problem started with the second episode of smoke coming out of the ventilation system and filling the cab... First time I thought I had burned out the blower motor. Motor still worked.. Then I though I had burned out some wire under the dash.

This year the smoke came back and I finally found the problem..

Problem was that a mouse built a nest in my air conditioner right between the blower and the evaporator. What happened was the wire resistor for the blower motor that screws into the air conditioner area had set the mouse nest on fire.

Took the blower motor out and the resistor. Cleaned the cavity out and then reassembled the components. Ever since then the blower only goes on high and I'm freezing in the cab...

Any ideas what is wrong? Have I blown a fuse? Any idea which fuse? Or, have I burned out the resistor. I did take out the resistor and it looked fine...

Most likely the resitor is shot. I have had it happen twice and the fan would only run on high.

whats the resistor? my truck does this same thing

It's on the heater box in the engine bay has 3 or 4 wires and look like this https://www.ford-trucks.com/forums/p...ictureid=37576.

Sorry for the poor cell image.

-Enjoy
fh : )_~

The plug with the 2 screws on either side is the resistor. Remove the plug then the screws and it will slide out. Usually under $30 at parts house.
http://farm3.static.flickr.com/2803/...88bfe825cb.jpg

87crewdually and Festus, Thanks for the pictures. My 85 is a little different, 3 separate wires to the resistor, no plug, but its located in the same place. I think its shot, when I took it out last time after the smoke it was embedded with burnt wood chips.... Off to NAPA this afternoon.

I believe if you think your saving electrons by putting the fan on low your not, just sending some of the energy through the resister and putting off heat instead of turning the fan faster.

redbug, there should be 4 wires, unless it's only a 2 speed switch in the cab. (Should be one for each speed, plus the... let's call it a return, as I don't think it is actually a ground.) A common issue on these is corrosion at that plug, I've had to dismember a couple of them and use spade terminals on each wire. Bit of a pain if you need to take it off later, but unless it's not working, something you rarely touch anyway.

Ok, I could be off on the number of wires. Will check tonight, thanks.

I believe, If you have factory A/C you'll have 4 wires, if you do not have factory A/C you'll have 3 wires.

Though don't go to the bank on that ...

-Enjoy
fh : )_~

My 88 had factory a/c and has 4 wires. The 81 doesn't have a/c and has 3 so you may be right festus.

I had an '84 Ranger in the past and dry leaves got in that resistor and caught the truck on fire! It was a roaring blaze before I got it put out. The resistor is actually in the ground wire for the blower motor. Running the ground wire directly to ground gives High speed on the blower. Running it through the different resistors gives you the slower blower speeds. As you can see the resistors are made of different diameter wire to vary the resistance and thus the blower speed. Those resistors get red hot and that's why it's mounted so that the resistors are inside the blower air chamber.

Wow, too bad about your ranger... Maybe I should put remove blower motor yearly to check for leaves on my maintanence list...

Ordered new resistor. Old one does have four wires. One lone connector and a three plug connector. My local NAPA did not have it and could not order it. Advance auto had it for $30.

You're lucky that yours only smoked and didn't catch fire.

The louvers in the cowl (between the base of the windshield and the rear edge of the hood) on the 84 Ranger were slots about 3" or 4" long and 3/8" wide. I now have a 01 Ranger and it has a bunch of 1/8" holes punched in the cowl. Don't tell me Ford was not aware of the problem of leaves falling through the slots and getting into the blower chamber and then into the resistor.

I'm sure Ford was aware of it... My father was in manufacturing for over 40 years, he always says "There is no isolated incidence, if one fails, they all fail".

My house is surrounded by old growth forest, maybe its time for me to put a screen over the louvered vents...

Picked up the resistor today, installed it, I now have 4 speeds on the fan... I'm not in an ice box anymore!