When i accelerate, the fan blows?

Question

Under acceleration, the outlet for the windscreen demister blows air quite violently.

Anybody know what might cause this?

Its a Ford Focus TCDi.

Answer 1

sounds like a vacuum hose has come off. where i don't no so i can't be any help. sorry, best bet is to have a hunt around the engine bay and try and find a pipe that is not connected.  

Answer 2

get your voltage regulator checked asap

Answer 3

just clean your battery cables for now and see if that changes anything.