1986 ford f-150 wont change from vent to floor to defrost

[NFord]

Hi and Thanks for any and all help you guys might provide. My truck recently quit blowing air from defrost or the floor when I move the selector switch. There are 2 vacuum controls and both seem to be working properly so I know I have good vacuum. When I reached up inside to see if the doors were moving when I moved the switch around the one door "the lower door" and Not the temp selector door as the temp does change just not the air flow, the door felt very loose. I went to the local junk yard and tore out the heater box in another f150 and was able to visually see that the same door was also loose and floppy? I could not see any anchor or pivot points that may have been broken or out of place and so I just came back home bewildered :-( Thanks again .... NFord
P.S I may forget to check back here as I am pretty busy this time of year. My e-mail would work better for me to check. yldlrow@yahoo.com TY