On your thermostat, the setting marked fan determines whether the fan on the air conditioning unit will run all the time, or cycle on and off with the air conditioner. However, when you are running the furnace, the setting will determine if the fan (air conditioning fan) will run when the furnace is on.
Move the thermostat to the "fan" position and you will see Hi, Lo, or AU (for automatic). Use the + and - key to change settings. Then move thermostat to Air Conditioning or Furnace, as desired (or Heat Pump if you have that option. Here's how the fan setting will work:
When the furnace is on, the fan setting of AU (auto) will keep the air conditioning fan off at all times. (That's the air circulating through the upper air vents (ceiling). Only the furnace fan will cycle on and off as needed (lower air vents that blow hot air). If the fan is set to Hi or Lo, then whenever the furnace and its fan come on, the air conditioning fan will also run on hi or low speed. Hot air will come from the lower vents directly out of the furnace. Cooler (room temperature) air will circulate from the upper vents.
When the air conditioning is on, it works a little differently. In the auto position, the fan will come on only when air conditioning is needed. It will switch from high to low as needed to meet the demands of the thermostat. With air conditioning selected and the fan on hi or low, the fan will run continuously at the selected speed and the air conditioning compressor will cycle on and off as needed to cool the MH.
If you have the optional heat pump, the fan control will work like it does for air conditioning. Heated, but not "hot" air will come out the upper vents.
Sometimes running the AC fan with furnace can spread the heated air out more evenly. Running the fan continuously with the AC on can do the same, plus provide a sound dampening "white noise" when you have loud neighbors.
2012 Forest River Sunseeker 2300 Chevy