So far I have removed the blower fan and this all seems fine and voltage ok, cleaned and lubricated and put back. Whilst I had drained the coolant I needn't have bothered as I managed to get the motor and fan out without removing the whole heater unit as instructed to do in the manual.
The vacuum for the fresh/recirculating air switch appears not to be working as it's not moving the flap behind the vents on the bonnet.
Could anyone tell me if it is possible to trouble shoot part of the system?
The switch and tubes are all connected but I don't know how to trouble shout the solenoid or vacuum unit (under the dash) and vacuum reservoir (ball thingy) under the bonnet?

Thanks for all the input on this. I managed to repair the vacuum unit (under the dash) that wasn't allowing me to switch between recirculate and fresh air.
Taking a meter reading from the heater blower motor I'm getting just under 12v! I would normally have expected a little more with the engine running so perhaps I'll try to hotwire to the battery and see if this makes a big difference in the fan's output.
Whilst I've go the dash off I've started messing around with the a/c but will re post my questions re that in a new thread.
Just wanted to say thanks for all the help and advice.