stick your head under the drivers side (down in the foot well, then look up and left when your head is down there behind the sereo) and get someone/or yourself to cycle through the modes (ie. face, face feet, windscreen etc etc) you'll notice a white arm moving or not moving. this is what makes the air change direction. if its not moving, you might find that the plastic teeth on one of the plastic cogs has warn out, try sourcing one from a wreckers, or speak to nissan again (even by taking the piece into nissan spares so you can show them exactly what you want)