I have repaired the blend door with a crafty repair I found on another site. Turns out this is a common problem for some time. And, an expensive one repairing it in normal fashion, 100+ in parts and hundreds of dollars labor. According to Ford, you must replace the air handling plenum by 1) discharge the AC and remove the evaporator housing. 2) lower the steering column and remove the entire dash assembly 3) remove and replace the plenum; then reinstall dash and AC evaporator and recharge system. I must say this is one of the biggest fiascos I have encountered in my 40 years of experience owning and maintaining vehicles. It's just plain poor design on the blend door and absolutely no maintainability engineering done to ensure a reasonable repair process iin the case of failure. The crafty fix you ask?
Go to the Ford truck forum
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and find the"free blend door fix" postings for "Jfrank" and "talon dad" Then findtheir photo gallery postings (you will need to register and spend a bitof time poking around) and you will have detailed instructions withpictures for how to effect a repair. It took me less than an hour todo and cost nothing. So my system is now working normally. A sidebenefit is by not doing this major dissassembly is you avoid thepossibility of MIF (Maintenace Induced Failure) of other parts.