If the hoses going to it are both hot then it sounds like you've got coolant flowing through it. You can disconnect the hoses from the heater core and blow some air through to confirm if you have doubts. It sounds like the door isn't moving properly. The actuator might move but if something is broken (like the part where it attaches to the door) then the actuator will move without actually moving the door. Do you have a borescope you can put in there to see if the doors are moving?