intermittant heater blower!!

[charlie brown syndrome]

i dont know whats going on with it, it doesnt seem to have any set pattern as to why and when it works,
i thought it was something to do with the eberspacher that ive got in the van (which incidentally doesnt work either)
ive changed the switch itself as the round plug that goes on the back with the 4 wires on has one of the wires snapped and another one hanging on by a thin strip of wire, so ive chopped out the rotten cable and ran a new bit in,
could it be the motor itself? when it does work, which isnt very often it seems to blow ok with no nasty noises or strange smells,
also would it fail the mot on this as it doesnt have a windscreen de-mister?
thanks in advance