There are little electric motors that control the airflow and temperature to the different vents for in the dashboard. These motors are called "Actuators". I believe this other user is saying the actuator that controls the blend air door is defective. The blend air door controls the temperature of the air, so I'm not sure this is right, but either way, the system that controls these motors or one of the motors themselves is where the problem lies.
A shop with the appropriate diagnostic equipment should check the system to see which actuator may be malfunctioning.
Hope this helps.