During initial use, "snapping" sounds may be heard. This is normal, and the unit may continue to make these noises during the first few days of operation. After this initial start-up period, only an occasional "snap" will be heard, indicating the unit is cleaning your air. Note: As the air cleaner’s electronic cell becomes dirty, it will "snap" more frequently. When this occurs, you should wash the cell.

Visit BuyFriedrich.com for more details on the C-90B or to order replacement filters online.