AC only blows through defrosters

As stated in the title, air only blows out of the windshield vents. I can change the speed, and the air blowing doesn’t get too hot or cold but I will charge with Freon after I fix the issue. I’m not sure if the blend door needs to be switched or if there is a leak in a vacuum.

2004 Expedition 4.6L

If your vehicle uses vacuum to control mode doors, then you most definitely have a vacuum leak- usually at or near intake manifold where rubber and/or plastic hoses get brittle and break....

For safety reasons, if vacuum supply is lost, the doors are spring loaded to default to defrost to be able to clear the windshield if they fog up.

To check the vacuum line, you need to remove the battery.