A/c Heater only blows threw defrost vents

1997 Jeep GC, the a/c and heater only blows through the windshield defrost, I can turn on the A/c and it blows cold through the defrost vents, I can turn on heater and it blows hot through the window defrost. I turn the switch off and it shuts off. Any ideas
Thnaks for your help
Dave

If you have ATC Automatic Temperature Control the system is all electrical. If you dont it works by vacum and electrical. Check the blend door under the passenger side dash to see if there is any blockage from the door not opening. Could be a bad control switch or vacum leak. Just a few possibles.