Suburban Furnace Low Air Flow Switch 230509/233356 (NT/SF Series) 525024 Compatibility: Suburban Furnace  NT-30/34 M S SP NT-25/ 30/35 K P-30S SF-20/25/30/35 SF-20/25/30/35F SF-42 42F (BELOW SERIAL NO. 924201894) Features Limited 90 Day Warranty