Pop out your counsil using a screwdriver with a cloth or something wrapped around the head so you don't scrach your plastic. Look for any abnormalities behind the unit.
Also in your pedal well, look up for a little thing that looks like this.
This is the AC control arm. In the picture above, it's in the "neutral" position on the knob. Notice the little wire attached to the white arm. This contols everything heat and cold wise.
This next picture is in the "full Heat, or red" area on the knob.
Note the position on the white thing.
This is it's postion of the arm in the "Cold, or blue" area
just make sure that this arm moves smoothly from full heat to full cold, after that, take it to a dealership.
If the pictures don't show, check the attachment.
EDIT: what is a FREE image hosting website that is combatible with this forum?