My air conditioning vents are not working in my van the air is only coming out of the defrosters and not anywhere else what could be causeing this my uncle had this van and it worked fine and then it broke down and sat for 2 years until they gave it to me and i rebuilt the engine and now the air will not stop blowing out of the defrosters in the summer during when it is real hot this not help at all is this somrthing i can fix my self?