What is the most common reason for Audi Air Conditioning system not working?

I've noticed that my Audi air conditioning system is not working properly. The air is not as cold as it used to be and sometimes it doesn't even blow out at all. What could be the root cause and how can I fix it?

The most common reason for Audi air conditioning system malfunction is low refrigerant levels. It is recommended to take your car to a certified mechanic for proper diagnosis and refilling.

Another possible reason could be a faulty AC compressor. If you hear strange noises coming from your AC unit, it's best to have it checked and replaced if needed.