what does it mean if my heater is blowing cold air

Hello, The buzzing sound tells me that the blend door actuator is working, but the blend door is not moving, is stuck, or is broken. What are those, you ask? The blend door actuator is a small electric motor that turns the blend door. The blend door is inside the air conditioning and heater (HVAC) ducts, and when you select a certain temperature, the actuator turns the door to allow hot or cold air through to the vents. You will need to remove and inspect the actuator that is making the noise, and, if it is broken, replace it. If the actuator is good, and the blend door is broken, the dashboard may have to be removed to replace the blend door.