Mine  was replaced under warranty about 2 hours in and out. the dealer told me it was a common problem and stocked the parts. I was told the part [blend door motor] runs about $30 and labor is about 2 hours.
I don't know what your warranty status is but if its not covered due to time or miles you might contact ford and see if the will work with you as a curtisey replacement.
Iff you plan to do it yourself the radio must come out to access the motor