I bought a 2007 A4 this winter. When the weather got warmer I turned on the air conditioner and there was a very musty smell that lasts about 10-20 seconds then goes away. It continues to happen every time you start up. Can anyone help?

 

Try cleaning out the area where the cabin air filter goes and/or replacing the cabin air filter.

Bad Smell From Cars Air Conditioner | Suite101
What's the musty smell coming from my A/C vents? - Ask.cars.com