Hello Gregory,there are 2 ways to do this one is to replace the door,a company called Dorman does makes a replacement so you don't have to replace the complete plenum assy. You would still have to R and R the unit to do the job. I have done it another way on 2 of our trucks,I was given this fix from a Ford tech,some agree with it others call it a hack repair,you decide. After removing the glove box, you remove the electric control on top of the heater box, a tight area,but you can do it.Have the motor in the heat position first,then make sure you get the door turned to the heat position. You then drill a hole in the motor shaft,to accept a 1/8" cotter pin,make the hole a little smaller so it has a slightly tight fit. Then cut off the ends of the pin,leaving about 1/16 " sticking out of each end ,the reinstall the electric actuator. Sending a picture of how it looks and the information on the replacement door,Good luck,Jerry.

http://www.dormanproducts.com/cgi-bin/vm91corp30r/classdtl.p?clt=hwrap1&sid=0x01348c56&tid=44685&rid=0x000461dc