i'd have to think your problem is related to a bad vac pump or broken linkage.

if you can get the vac tube off, and put another tube on the pump, if you blow or suck the tube the arm should move.

you could even try to take the arm off, be careful with it so you dont break it, i've never had to take one off so i cant help with that part, but once its off work the linkage by hand and see if you get air to flow all at once to one setting or another.