Yes the F150 and the F250 are the same.
You can only get at it from inside the cab.
All blend doors are cable controlled.
Yes you have to take out the 10 screws to see it form inside along with the glove box. This allows you to remove items that may have fallen down from the vents and blocking its operation.

Note that the cable control is on top and if that is the problem you can get at it with out removing the 10 screws.

Blend door control:





The ten screws:


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