The heat in my F150 works only when i’m going down the road. When I come to a complete stop, it doesn’t work at all. It seems like it could be the blower motor, but I wanted to come here first to see if anyone else has had this problem.

 

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Do you hear the fan or feel air coming out of the vents, have you checked the #51 fuse or #3 relay. If these appear to be working it there is also a Blower Motor Resistor. You need the right Blower Motor Resistor also, the one showed in the video is for the Manual heat and Air, the Dual automatic is a different part number.
Now is your coolant level OK? If it is low it might need to be circulating faster to reach the heater core.

 

Check your coolant level.

 

Please clarify what you mean not working: not getting hot? not blowing out the lower ducts?

 

Best guess is no blower motor, but i would suggest that's really easy to test by turning up the fan and seeing if you get air out the vents.

Fans blow air.
Heaters heat air.


Decide what you have/have not, "heat not working" doesn't mean anything.