Chances are its not a fuse but a lack of freon. If you can turn the knob and the fan in the car works, then its a leak in the ac system and you are out of freon.
Take it to a garage and have them do a pressure test on your ac system. If it fails, have it fixed and re-charged.
Over time the seals in the system start to dry out and crack and leak the pressurized freon gas. It just needs a re-charge. There are DIY kits, but its not worth doing it yourself.