I recently bought a 2001 audi a4 2.8 quattro and the ac stopped working yesterday. For a few days the ac was making a loud noise but the ac was still working then all of a sudden it stopped and no air comes out. All the lights still light up when i press the buttons. Climate control is not on. I can hear the ac turn on when i press the buttons but just no air at all. Do you know what it might be?