[Sean Marconette]

With pneumatic actuators we apply pressure, and with a pressure above what is above the actuators spring pressure it will move. In this case its vacuum, but the same principal. With the 17-21" w.c. rating of the vacuum pump, the actuator should stroke to the full position, and remain there. With what you are describing chances are if you apply 17-21" of vacuum directly to the actuator, if it moves and stays fully stroked, it is fine. Work backwards from there until you find what is damaged or unhooked. It could be as simple as the vacuum line is disconnected or cracked at the actuator.

Sean