Where is the cabin filter please
 

The blower sounds like its working away furiously though the vents blow little air and as has been said it might be the resistor. I am wondering could it be a clogged cabin filter. ?

In my 2002 the filter is beneath the glovebox, pretty easy to find.
I cleaned it with my Dyson vacuum cleaner :)

Could it be a clogged cabin filter? Sure easy to eliminate as the problem. Just remove it and see if it makes a difference. This video depicts changing one on a US Spec Dodge Grand Caravan. I'm guessing yours will be on the other side of the dash.

I will try that, thanks fella