when l turn on the heat the car does not blow nothing but cold air out. l have gotten the thermostat changed and replaced the heater core. by the way the nobe to that controls the heat and air goes all around could it be the actuator box? could someone please tell me what could be the problem.thank you

Blend door motor.

that is it the blend door is not operating its stuck on cold. Did you have all that work done to fix your heat problem? someone should have known that right away. In most cars its very difficult to get to so the repair can be very expensive like $500 or so for labor. In some cases you can reach the blend door level maybe through the glovebox and just turn it by hand. have someone check that out for you.

Honestly, this may sound silly, but if you keep things on your dash board, like pens and such, it may have fallen in the way of the actuator box door. You might hear the door flapping open and closed.

Also could be a vacuum line/hose located in the dash board that is disconnected or leaking preventing the opening and closing of the door of the actuator box.

Good luck.