Blower motor only works on high

[None2Slow]

My blower motor only works on the high speed. 1 night it was fine, in the morning only on high. Where do I start to look? Any links? The temp and postion controls still work fine.

[BryceB]

You need a new blower resistor. Check out ths video
YouTube

[NoRalPh]

The VAST majority of them aren't actually bad... The resistor board used poor quality, steel for heat, plug terminals. Chances are, yours are rusty & corroded making a bad electrical contact.

Take it out and clean the plug & "spade" terminals sticking out of the board and you might fix it all. In the mean time, depending on how bad it looks, you can order a new resistor board AND plug

[Bakes168]

I have the same problem...
Where do you start to clean all this stuff? Is there a video or write up on it anywhere?

[NoRalPh]

If you look at the blower housing (pass side firewall, under the hood) you'll see a square 4-prong plug going onto a removable board (often red), between the fan motor and the AC accumulator.

This is where all the trouble is. Take out the two screws that hold the resistor board in and remove it. Sometimes the corrosion is so bad you can't get the plug to come off the board Because the wrong materials were used (again the heat the resistors create has to be accounted for so, they're not brass) both the plug and the board have corrosion. Dorman and others make replacements it's so common. Even eBay and Amazon are full of them...

If you can get it unplugged, all you need is to restore a good connection in most cases. You can easily determine if the board is bad by just checking the wire resistors for continuity.

To clean everything I use one of those really small, hand-held sandblasters on the board and do the best I can scraping the plugs terminals. Then a light coating of grease helps prevent it from corroding again (not too much, this stuff does get hot and might smoke ).

[None2Slow]

In the 1st reply he posted a link to a youtube video. Thanks guys for the help, now to go fix it.

Here it is if you missed it....

How to Install Replace Heater AC Fan Speed Resistor 99-07 Ford F250 F350 Super Duty 1AAuto.com - YouTube

How to Install Replace Heater AC Fan Speed Resistor 99-07 Ford F250 F350 Super Duty 1AAuto.com - YouTube

[NoRalPh]

That's a great video!

For whatever reason, I couldn't get the link in the first post to work for me, but, we obviously were on "the same track"

[Bakes168]

Pulled the board out today and was able to get the plug off, there wasn't to much corrosion in there. I cleaned everything as best I could and put some dielectric grease in there. Still not working...
What's the next step? New resistor? Could it be something else?

[NoRalPh]

I don't think it's gonna be anything else... You have power there (HI works) and it seems unlikely the sw could only be bad in those speeds. But, it's pretty easy to check once it's in your hand

Visually, you can look at the resistor wires and the "crimp" that holds them. To be certain, an Ohm Meter will confirm continuity between the spades and through those wires.