Bongo Fury

does sound as though something is amiss inside the heater box although I've not heard of anything like this. I don't know why the blower should go onto full power when on recirculate and not on normal. all the cables should move easily and smoothly so if you are needing to move the levers manually chances are there might be an obstruction behind the control panel not allowing the cables to move properly. I'd pull the heater control panel out and have a look at what is going on behind. You'll need radio tongs to get it out.

If you don't have the tools to remove the radio you can often make them from a wire coat hanger.

Or 2 teaspoons with skinny handles.