i have2003dodge2500ram good air t flow to def vents but little to no heat coming

Hello, Inside the air ducts are little doors that change the direction of air flow, and change how much hot or cold air can get through to the vents. They are actuated by blend door and mode door actuators, and the actuators are located on the exterior of the case. If a fuse goes out for the left side blend door, there is going to be a failure to change from the current position. Same goes if the actuator fails or the door breaks. Check the fuse first, then check to see if the blend door actuator is running, making the noise, or silent when you change the temperature. This is a common failure item, but ensure the blend door itself is not broken off where it connects to the actuator before replacing the actuator.