Genuine Fujitsu 9379572002 Indoor Sirocco Casing B is the sirocco fan casing in the indoor unit, the housing that shapes and directs the air the fan moves. A cracked casing leaks air and noise, so the fan moves less air where it is needed. A genuine Fujitsu part is made to the same design as the original, so it goes back in the way the indoor unit was built.