How to Run a Central Air Conditioning Fan With the Thermostat Dialed Up


Central air uses the fan or blower in your furnace to circulate cool air throughout your house. Without the fan in your furnace, your house would not be able to maintain a cool temperature on hot summer days. But on mild days, it is useful to be able to circulate the air in your house, even when you don't want to use the air conditioner. By just running the fan on your central air unit, you can save yourself the expense of conditioning the air, while still maintaining a pleasant home environment. There are many benefits to running the central air fan continuously, but one drawback is price. It may add between $150 to $500 dollars per year to your electric bill, as of 2010.

  • Make sure that the registers in your home are open and free of obstructions. This includes the return air grills. Registers and grills can be located in the floor, wall, baseboard, or ceiling. They are made of metal and have slots where the air comes out. Many times, registers will have a handle that allows you to open or shut off the airflow. Check behind couches and under beds to make sure these are not blocked or closed.

  • Set the temperature on your thermostat to a setting higher than the temperature inside the house. Some thermostats are push-button and some have a dial or slide to increase or decrease the temperature. If your thermostat does not display the current temperature, mount a thermometer on the wall directly next to the thermostat. Remember that when the thermostat is switched to cool, the higher you set the temperature, the hotter the house will become before the air conditioner comes on. For example, if you set the thermostat to 75 degrees, and the house is 73 degrees, the air conditioner should not be running.

  • Locate the fan switch on your thermostat. Most thermostats have two switches and a dial to set the temperature, or an "up" and "down" button. One switch is the system switch, which allows you to select "Cool", "Off" or "Heat". The other is the fan switch, which allows you to choose between "On" and "Auto". On older round thermostats, the fan switch is located on the top of the thermostat. On older rectangular thermostats, the fan switch may be on the top, side or bottom. Many newer thermostats have a door that closes to conceal the fan and system switch. Open the door by pushing on the center to pop open the door. Alternatively, pull the sides of the thermostat to open the door and expose the fan and system switches.

  • Make sure that the system switch is set to cool. Set the fan switch from "Auto" to "On". This will allow the fan in the furnace to run 24-hours a day, or until you switch the fan back to "Auto." With the fan switch set to auto, the fan will only come on when there is a call of heat or cool at the thermostat.

  • Feel near the registers to make sure the air is now blowing from your central air. Check the outdoor unit to see if it is running. The outdoor unit may turn on periodically to keep the house cool when the temperature rises above the point you have it set to, on the thermostat. The fan should continue to run constantly.

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