Air Conditioner only works on the driver's side

The driver side vents blow cold air but the passenger side blows hot air. It does not have duel climate controls in the temperature settings unit but it does have a hot/cold wheel located on the dash between the dirvers and passenger vents, right in the middle. I have set that to cold setting and it still blows hot air on the one side. Why? Is this something that I can fix without any special equipment? Is there a relay or something bad?