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.

Asked by for the 2006 Hyundai Sonata
Perhaps re-visit the dealer - hopefully it's a quick vacuum line repair.