Hyundai Repair: My Defrost vents do not work...., 2003 hyundai elantra, hyundai elantra

Question
I have a 2003 Hyundai Elantra and my air and heat work great but for some reason my window defrost will not work. I turn on the heat and turn the dial to defrost and the hot air comes out of the air conditioning vents. ( on ANY turn of the dail that happens also)  I cannot seem to get the air to flow from the defrost onto my front or back windows or anywhere else for that matter. Thanks for all your help in advance.....

Answer
The mode control works via an actuator on the heater box.

To check the system:
-- By changing various settings on the control head, determine which actuators are for temperature, mode, and fresh/recirculated air.  You're primarily interested in the mode actuator.
-- Check whether the lever on the heater box is correctly installed into the actuator.
-- Remove the actuator and be sure the lever and cam articulate properly and that moving the lever easily changes the air output to the desired position.

Most likely, the lever has come loose or the actuator has failed.