Why Doesn't My AC Blower Stop When My Furnace Reaches the Designated Temperature?

A running air conditioner fan blows produced heat or cold air into the home.

Thermostat

The fan blower should stop when the internal compressor stops.The fan blower should stop when the internal compressor stops.
If the fan blows unbidden, the fix could require something as simple as a setting change or as complicated as a rewiring of the unit. Before poking around the circuit breaker or the air conditioner’s internal electrical work, the circuit breaker should be shut off to staunch the flow of electricity to the unit.

A broken thermostat could cause the air conditioner unit’s fan component to continue to blue long after the heating or cooling element shuts off. Under normal circumstances, when the thermostat temperature setting is reached, the furnace and the fan both shut off. It’s possible for the thermostat to either be miswired to the fan component or to be broken and cause only the furnace to shut off while the fan continues to run. If you suspect a problem with the thermostat, you can contact a technician for repairs or a replacement.

Wiring

Electrical power supply wiring gives power to the unit, but if there is a miswire from the circuit breaker to the air conditioner, it’s possible for one or more components to fail to turn off. After the breaker is shut-off to stop the flow of electricity to the unit and prevent electrocution, all electrical connection terminals should be inspected to confirm the correct connections. If rewiring is in order or you suspect a miswire, contact a technician for help.

Fan Only

Some units feature a “Fan” mode button. If the fan is set to run regardless of the current air conditioner mode, then it will run even after the air conditioner or furnace has shut off. The fan mode helps circulate air within the room. Some units even feature a “Fan Only” button with the sole purpose of activating only the fan when pressed. To deactivate the fan mode, select the appropriate mode button, such as “Heat,” “Cool” or “Energy Saver.”

Power

It’s possible the unit might have suffered an electrical episode, which causes it to not function correctly. You can either unplug the power cord from the wall outlet or shut-off the furnace power breaker to reset the connection. Allow approximately 15 seconds to pass and then reinstate power to the unit. If the fan still continues to run when the unit is turned back on, there might be an internal wiring problem within fan motor. You should contact a technician to look further into the problem.

About the Author

Whitney Houston began writing in 2006. Her work has been published in "BUST" and PaperDolls magazines. Houston attended St. Edward's University, graduating with a Bachelor of Arts in photocommunications (photography and digital imaging).