airflow from the heater/AC works on floor and defrost, but not the vents?

The airflow from the heater/AC works on floor and defrost, but not the vents. I'm wondering where the control actuator is that directs the chosen flow and if the issue could be a faulty actuator. I'm also wondering about an alternate reason for the lack of air being directed to the vents. The defrost vent up by the windshield has many pieces that are broken and missing. (We bought the car used and if was this way.) What I'm wondering if some of these broken pieces fell down into the duct work and are blocking a door from moving that would direct the air to the vents. For what it's worth, there is no discernable sound when I change the setting from floor to vent, for example. Nothing that sounds like an actuator is struggling to make the change.