2003 Dodge Ram Heat blows cold on driver side

When climate control is on heat, either on the floor or vent mode, it blows hot air on the passenger side and blows cool on the drivers side. When it is on defrost mode is the only time it blows equally warm air on both sides. The temp. control actuator is working and the actuator to change from defrost to floor vents is working too. I'm afraid its something deeper inside that I can't see I will have to take apart the entire dash board to figure it out. Help!