2003 Ford Expedition air only comes out of defrost vents on all settings

Sounds like a vacuum leak.

The vent blender module is defective. Accessible behind the glove compartment.

As Maxwell Smart would say " ah, yes Chief, the proverbial no air out of the vent trick." Open glove compartment, release tabs that hold door from dropping down. Get flashlight, look in the compartment to the left, you will see a small motor looking thing with a plastic arm attached to a metal rod. That accuator moves the settings from vent to floor to defrost, it swings a deflector plate inside the blower assembly to direct the air where you want it. Previous owner paid over $250.00 to have the cheap plastic arm break again. I marked with whiteout "summer" for direct vents through the dash and "winter" to bend dash and defrost. I have to manually move the arm up or down while testing where the air flow comes from. Check YouTube for videos onhow to patch it. Same mucho dollars and open the glove box up 2 times a year and move it manually to the settings you want .