2004 Touran fan not working

[Doghead19]

Hello
I've recently bought a 2004 Touran, and have encountered a problem with the fan. Basically it sounds like it is working, but no air is coming out of any of the vents. The only time we get anything coming through is when we put it in reverse! Very confusing, but I wondered if anyone could clue me in as to what the problem might be?
Cheers!

 

[Crasher]

The air inlet for the fan is under the windscreen in the plenum chamber and covered by a plastic Meath, my guess is this is covered with debris but getting at it means taking the trim off which can cause you to crack the screen and you have to take the wipers off so remember the left arm on twin motor tyres uses a left hand thread and special nut. The reason I think this is when you go into reverse, the body control module 5ells the heating ventilation air con system (HVAC) to close the external intake and take cabin air through, so preventing you from reversing through your own fumes, handy with fuel of the Devil. If you press the recirculation button, this should have the same effect.