Bill
intermitant cooling out of the center vents is normal, if none then you may have some bad vacuum actuators or lines off the hub.
I will have to look but I think the actuators for the defrost vents are behind and above the push button unit. YOu can get at them but they require some effort. You can remove side panel and see if they are working. This most likely is your problem. They can be fixed with an actuator kit. I got mine from George Murphy. Also there are actualtors behind the glove box that are easy to reach and see if they are working.
Are all of your other vacuum functions working, unlock system?
If not you may have a bad vacuum pump or leak.
May need a mitivac to check
Glad to hear you now have fan :D
Good job!