The other evening I was in slow moving traffic behind a particularly smelly car and when I tried to turn on recirculation, nothing happened. I tried it a few times over about 30 minutes and assumed a fuse or relay had failed but eventually it did come on. I tried all combinations of aircon on/off, hot/cold etc but I don't know what fixed it in the end. I can't imagine there's any reason to prevent it being used (and there is nothing in the manual) but just thought I'd ask in case anyone else has had this or if mine potentially faulty?