The Fan Controller automatically slows down or speeds up centrifugal fans to maintain the room temperature at a value corresponding to the day or night set points. Day and Night temperature set points: 50°F to 100°F. 3 position slide switch to select idle options: Idle Off-Fan will stop when set point is reached, Idle On-Fan maintains minimum (idle) speed when room temperature is equal or cooler than set point, Idle On with Low Temperature-Fan maintains minimum speed (idle) when room temperature is equal or cooler than set point but fan will stop if room temperature gets cooler than 10°F below set point.