Why does air blows on driver's side when heat is on

Hello, Your Lincoln has little doors in the heater and a/c central housing (big black box behind the dash). The doors always have hot and cold running to them, so, just like the water in a bathtub, the doors will turn until the proper temperature of air is flowing towards the vents. The one on the driver side may be damaged, the electric motor which turns the blend door (the blend door actuator) may be bad, or you could be having more serious problems with the climate control unit on the dash. Check your fuses before you seek a professional, and keep in mind they may need to remove the dashboard to get to the blend door or actuator.