91 Tempo Heater/AC Vents Stuck on Defrost

I need to know what to do to correct a vent problem. Regardles of what setting I use the airflow from the hearter/vent/AC will only blow out of the defrost vents. I can get a little out of the floor in heater mode, but it is not working correctly.

What would the fix be for this?

Im having the same problem with my gf's car. I've checked the fuses under the dash and removed the Heating A/C controls. All was in order and nothing even showed signs of stress for being 16 years old.

Check the small vacuum hose at teh top center of the firewall. I found mine broken; cut off the bad end and reinstalled on stub. The heating and a/c controls began working properly immediately. These controls are operated on a vacuum system.

Vacume sounds right, mine does the same, but fixes its self after a few minutes driving