Heater stopped blowing in all settings, except defrost.

Check the heater tap moves when you adjust the temp dial. A/C will not work with the heater on.

the flapper door is not closing and opening properly...it is located in the duct work....remove heater control panel and follow the cable to the flapper door

Check and see that the vaccume hose that leads to the controler is not cracked. Ford liked to use those hard plastic lines and they crack. become loose a the connections and melt if to cloose to exaust. Make a quick inspection from under the hood of any vacuume lines that lead through the firewall.

possible blend door in the dash is broke . when you turn blower on high it blows the door shut . i have the same issues and i have heard this could be the issue . especially since you said that you replaced everything except the blend door.

Here is a set of directions from another site, put into a word document. Includes some of the factory manual diagrams

Right click save as :

http://my.voyager.net/~sscully/F-15097HtrCoreRepairF150_Exp_002.doc

Hope this does it for you.

If it was a fuse it wouldn't blow at all. Check coolant level. Change thermostat. If still not working possibly a heater core - symptoms of a bad heater core would be losing coolant, fogging of inner winshield with defroster on or wetness on passenger side floor.,

AC blows where you have your control switch set,if it only comes out your defroster have the vacuum check at the blend air doors or if you have a faulty heater control unit.

You have a vacuum leak. Defrost is the default postion (no vacuum). Since it is working correctly in the ac postion I would suspect the problem is at the floor/panel door.This one is located on the drivers side of the heater box just to the right of the accelerator pedal.

change the heater core

does motor run on only one speed? if so replace the blower resistor.
if it just quit , check for power at the blower motor, if u go power then replace the blower motor