Problem with Heater/Cooling System

[rambaldi]

My Liberty started making this really strange buzzing noise from somewhere in the centre of the dashboard about a week or two ago. Today I realised that my heating and cooling isn't working properly anymore.

When changing between modes (face, feet, etc.) nothing changes, it continues blowing on my face. If I press the windscreen de-mister button all it does is blast hot air in my face instead of changing to the windscreen.

Looks like something is broken — any ideas as to what I need to look at?