Why Does the Fan Keep Running on My Air Conditioner?

Is the fan on your AC running and running … and still running? When it’s working correctly, the HVAC fan should turn on and off as the heating and cooling cycles on and off. An air conditioner fan that continuously runs is a red flag indicating you have a problem with your system.

Read on to learn why the AC fan keeps running on your unit. Learn how to troubleshoot and fix an AC fan that stays on.

What’s Happening When the AC Fan Stays On?

If you’re wondering “why does the fan keep running on my air conditioner?” Know that there are several reasons why your AC fan may stay on. The most common problems include:

1. The fan is switched to “on” rather than “auto.”
   When the fan is switched to the “on” position, it will run continuously. It should be set to the “auto” position, so it only runs when the air conditioner is running.
2. AC is too small for the property or can’t keep up with extreme temperatures.
   If the HVAC system is not the right size, it will not run optimally. A too-small HVAC system will run longer to try to keep up with the thermostat setting. Also, if the temperatures outside are extremely high and the AC is unable to reach the thermostat setting, the entire system, as well as the fan, will run longer than usual until it reaches the set temperature.
3. The thermostat is faulty.
   If the fan and the cooling system are running when they shouldn’t, there’s a chance the thermostat may require a replacement.
4. There’s a short circuit or broken relay switch.
   If only the fan is running when the AC isn’t, there may be a faulty relay switch stopping the settings you enter on the thermostat from being communicated to the fan. It’s also possible there is another wiring issue or short circuit preventing the on and off commands from going to your fan.

What Should I Do If the AC Stays On?

Not sure which of the problems is causing your AC fan troubles? Troubleshoot the problem in three steps:

1. Set your fan to “auto.”
   If the fan is set to “on,” change the setting to “auto,” so it’s only running when the air conditioner is running.
2. Turn the fan switch to “off” and back to “auto.”
   If the fan doesn’t turn off, even when you flip the switch to the “off” position, your system may require a thermostat replacement. Thermostat replacement is a job for an experienced HVAC repair technician.
3. Schedule HVAC maintenance or consider a replacement.
   If you’ve determined the problem isn’t related to the fan setting or the thermostat, it’s possible your HVAC simply can’t keep up with the thermostat setting. If that’s the case, regular maintenance may be enough to get the system running its best again. If not, it may be time to consider HVAC replacement from a licensed service professional.

Your Local Aire Serv Can Ensure Your AC Fan Runs Like It Should

If you’ve tried the above troubleshooting steps and are still experiencing problems, it’s time to call on the trusted pros from your local Aire Serv^®.

From expert air conditioner maintenance to HVAC repair, the team at Aire Serv has the tools and experience to get your AC fan running its best. Call the Aire Serv HVAC pros today at or request an appointment online.