Lost cabin vent control on 2006 Hyundai Sonata

I've lost control of my heater/ac vents. The air flow is stuck on windshield defrost. The temperature control works fine as does the blower speed control. I just can't get heat to deflect to the floor or a/c to come out the dash vents. This condition started intermittently and has now become permanent. It seemed to start soon after my dealership replaced the cabin filter.

1 answer
Perhaps re-visit the dealer - hopefully it's a quick vacuum line repair.