crosbo

Hi all newbie here.......... I have a 2007 2.8 crd grand voyager. The demister has stopped working although the blower is working perfectly at all speeds. I'm a bit lost as to what this could be, in saying that when it was working on demister mode I heard what seemed to be a whirring noise when the mode was changed. I am not a mechanic, amateur or otherwise so any help would be very much appreciated. Regards