Leaks

• Things inside of the home, such as open windows, open floor vents and unsealed baseboards, cause cold air to leak out of the home. If there are too many openings, the home can’t keep enough cold air in the house to reach the designated thermostat setting goal; therefore, the central air conditioner unit works overtime trying to cool the home, which gives the impression that the fan can’t turn off. All openings in the home should be sealed to give the air conditioner a break. The thermostat can also be raised to make the room temperature goal easier to attain.
  
  

Blockage

• Furniture, such as curtains and cabinets, can block the central air conditioner outlet vents inside the home, preventing cold air from blowing into the room. In turn, the thermostat sensor can't detect the cold air, so it “tells” the air conditioner and its fan to keep cooling. All furniture should be removed from the front of outlet vents so that cold air can enter the room properly. Once the cool room temperature meets the thermostat setting goal, the fan and the internal compressor shut off.
  
  

Filter

• A clogged filter prevents air from flowing into the unit. Without air entering the unit, there is no air to blow out of the unit. Again, this affects the thermostat sensor reading. The thermostat setting can’t be met if air can’t flow into the home, so the fan and compressor both continue to run fruitlessly, which continues until the unit is either turned off or the filter is cleaned or replaced.
  
  

Wiring

• The air conditioner power lines can be wired improperly upon installation or after repair. Lines that are wired incorrectly could cause the unit to either not turn on or prevent it from turning off. If you suspect that the unit is wired improperly and the fan fails to turn off when the room temperature exceeds the thermostat setting, you should turn the air conditioner off at the breaker and call a technician to look at the wire connections.