Turn the car to IGN ON and turn the music all the way down. On the climate control select a set of vents and listen for the mechanism trying to switch over. If you look under the dash you will se a set of plastic gears and arms that select what vents the air is being directed through. I've seen these plastic pieces break before and cause the air to be stuck on one set of vents. If you can't hear anything when selecting a set of vents then you most likely have an electrical issue like a bad relay or the climate control it's self could be bad. Just an idea.