Why does the air and heat blow out the dashboard and not the vents?

This HVAC system is controlled by engine VACUUM .. When there is an insufficient amount or no vacuum supply to the dash controller - the air mode switches to defrost by default .. The usually culprit is a vacuum leak under hood - passenger side near firewall .. Small black plastic vacuum tubing gets brittle and cracks or breaks thus the defrost mode is all that's available. Find and repair the leak in the vacuum supply circuit and your problem will be gone! We have no way of knowing ones auto repair skills - you may need *hands-on* assistance from qualified personnel. Good luck!