What works best for humidity, mold and air quality in Northeast Florida Look at your thermostat and you will probably see a small switch labeled Auto and On. It looks minor, but in Northeast Florida it can affect how humid your home feels. Humidity matters because mold grows where moisture lingers. The short answer When your air conditioner is cooling, set the fan to Auto. What the two settings do Auto: the fan runs only while the air conditioner is actively cooling. On: the