Auto Air Conditioning & Heater Repair: No heat, heater valve, possition

Question
I have a 2000 explorer XLT, i went to turn the heat on and all i got was cold air, i thought it could be from not using the heater for a while but it never changed over to heat it stayed cold.
The dial was on the heat side, and the other dial was on defrost symbol so it would blow heat on the front window.

Answer
Hi  the heater core may be plugged  or the heater valve may be stuck in the cold possition  or even the door in the case is broken at the place where the motor driven actuator ( right behind the glove box on top of the case)goes into the door check and let me know