How to troubleshoot a malfunctioning air conditioner in an Audi A4?

My Audi A4's air conditioner is not functioning properly. It's not blowing cold air and the temperature controls seem to not be working. What could be the cause of this issue and how can I fix it?

The first thing to check is your Audi's refrigerant levels. Low refrigerant can cause the AC to blow warm air. You can easily check this by using a gauge to measure the pressure in the AC system. If it's low, you can refill it with the proper refrigerant.

Another common cause of AC malfunction is a faulty compressor. If you hear strange noises coming from the AC unit, it's likely that the compressor is damaged. In this case, it's best to visit a certified mechanic to have it replaced.