If your heat is only working on your highest speed, chances are your resistor is gone. Here are some pictures of the location . 2 screws hold it in, 1 wire harness plugged into it.

https://www.f150online.com/galleries...5529&anum=9470

https://www.f150online.com/galleries...469-135528.jpg

https://www.f150online.com/galleries...469-135527.jpg

 

Here are pics for the 04+ owners with the same problem. I lost only speed #1 but still wanted to fix it. It is about $25 from the dealership.

The location is behind the glove box. The glove box doesn't need to be taken off just hang it down all the way. The two glove box screws are 7mm if you take it off. The resistor has two screws 8mm in size. I highly recommend using 1/4 drive ratchet because of the room (lack thereof).



**note- bigger pics in my new gallery (click on my name). And part number is 3F2Z-18591-AA.

 

Also go to....
F150online Forums > Special Interest > Articles & How-To's
Replace 04-08 fan blower motor resistor EMTC HVAC

 

Thanks for the instructions and photos. Part cost me $20.02 from rock auto (incl shipping), had it changed in less than 10 minutes. Have been without 1-2-3 for months, now it's fixed!

 

Perfect, glad to hear!

 

Another fixed resistor thanks to searching and pics!!! Thanks guys!

 

+1 Thank you. I love this site. Thank you wutagoalie for posting this.