EATC Air Distribution
Recirculated air is only used during MAX A/C, AUTOMATIC and OFF modes.
Air distribution within the vehicle is controlled by the EATC system in
the AUTOMATIC mode, but it can be overridden by the driver if desired.
Airflow control doors are used to direct airflow within the A/C
evaporator housing and plenum/floor chamber. Vacuum control motors are used to position these airflow control doors.
The air distribution system is designed to provide airflow from the
defrost nozzle when no vacuum is applied to any of the vacuum control
motors. This is done to prevent a situation where defrost cannot be
obtained due to a system vacuum leak. (AHA, there's a hint for you!)
There is an AC vacuum check valve under the hood against the firewall, that you can trace from inside the car.
You must have a kinked vacuum hose, broken vacuum line, or perhaps a bad AC vacuum check valve, would be my first guess.
There is also a vacuum reservoir tank, and the line to/from it might be leaking as well.