I am in the throes of the same thing... don't have any info for you but I am experiencing the same symptom in that my center vents don't work. Yesterday afternoon I was working on it and manually closed the defrost vent actuator while the car was running... the center vents came open and blew cold air... but it did not last long as it closed tight afterwards and the manual manipulation didn't work again (I am hoping against hope that it is not the center actuator but it probably is). Since I had both kick panels and the glove box out, I took a pair of plyers and grabbed a small white plastic piece on the a/c housing (through the glove box, turn left and just below the flex rubber duct material for the center vents. It felt stuck but stayed open after I opened it. I am going to see if this will keep it open but I think you are on to something as the defrost actuator holds vacuum but it is always on when I turn on anything from the temp control panel.. the Haynes manual is worthless in this endeavour and I don't have the cd rom discs that I understand are pretty good... so I have the same problem you do and I apologize I don't have any answers.... BTW, I am in Grand Island, FL, but not sure where Nokomis is..... is that in the panhandle?