The duct sits/connects to the air distribution case indicated by the arrow. Once air passes through this, as directed by the damper controlled by the mode actuator, there is nothing else in the duct between that point and the dash outlets.
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Just to make sure...you said that you
can feel air out of the other three dash vents but
not the far left vent. Correct?
If you were not getting
any air out any of the four dash vents, then I'd say either the mode actuator is out of sync/isn't working or the air door itself has dislocated.
The diagram is from alldatadiy.com. Subscriptions are pretty cheap.
When you press the recirc button, it closes the fresh air intake damper and air is drawn from inside the vehicle. With the blower removed, you can see the damper behind it.