I'm having a similar problem with the AC. Pull out the glove box and the plastic cover behind the glove box so you can see all the plastic tubes that control the HVAC guts. Look for one or more that might have come loose or are split or frayed. It looks like there are 2(that I can see so far) diaphragms that push and pull levers to change the flow of air.
I have pictures which may or may not help you in your quest!
The air box closed to accept outside air only.
The air box open for recirculate mode.
One of the diaphragms, this one happens to open and close the panel for the pictures listed above.
What a typical air routing hose will look like.
