my dad runs a 51-plate 1.7 cdti Club estate as his co car, and whenever he carries one or more passengers the windows steam up like mad
He sticks the heater on (or more usually, my mum does...!) and nothing happens except a little bit clears on the front door windows - the windscreen does nothing. So you have to resort to having the windows slightly open so that you can see enough to drive...
its been to a garage a couple of times, but to be honest, I think he's forgotten to mention it from the word dot, so it never gets seen to.
any ideas what it could be? and how best to go about fixing it??