If you can hear the fan/blower running, then it is likely to be one of the 'diverter' units between the fan and the outlet that is either blocking the airflow or directing somewhere other than you expect, maybe blowing at the windscreen ?
Edit - Just re-read your post, are you saying that air is coming out, but it is not getting heated ? In that case it is likely to be the mixer/diverter that controls how much cold/hot air gets mixed. I don't think the D40 has a valve that controls the coolant running through the heater core, but I may be wrong on that. It could also be a blocked up heater core from minerals in Aussy water, have heard of some radiators there getting blocked up.