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Why does the fan keep running on my air conditioner?

Air conditioner fan next to leaves
Here in the Kansas City metro area, air conditioning is practically essential for survival in the summer months. On a hot day, it doesn’t take long to realize when your home’s air conditioning isn’t working properly. Even if your house is being cooled, it can be concerning when your HVAC system behaves strangely.

4 reasons your AC fan won’t turn off

Diagnosing air conditioning problems is what the professionals here at A.B. May do best. In our experience, these are the most common reasons why an AC fan keeps running.

1. Your system is unable to cool the room or home

Sometimes the simplest explanation is the correct one: if your AC fan won’t stop running, it might be because it’s unable to cool the room to the desired temperature. This may be because you have the thermostat set too cold or due to poor insulation (cool air escaping the room or house).

2. The thermostat is set to ON instead of AUTO

Another relatively simple explanation is that your thermostat could be set to ON, which tells the system to run the fan constantly whether the air conditioning is cooling or not. 

3. Your thermostat is malfunctioning

Your thermostat is more than just a device where you set the temperature; it also senses whether the room has gotten cool enough to shut off the AC. If the thermostat is no longer able to accurately tell the temperature or relay information to the HVAC system, it may need to be repaired or replaced.

4. Electrical issues between thermostat and HVAC system

While this issue is similar to a malfunctioning thermostat, it’s not quite the same. Your thermostat may be working properly, but if the electrical relays and switches that connect it to the HVAC system are faulty, it won’t be able to regulate when the AC fan turns off.

How to fix an AC fan that keeps running

1. Make sure the thermostat is set to AUTO, not ON

Simple problems often have simple solutions! If your AC fan is running constantly because of an incorrect setting, you can simply switch the thermostat to AUTO (or OFF, if you don’t need the system running at all) to fix the problem.

2. Troubleshoot thermostat temperature settings

One way to help identify what might be causing the problem is to change the temperature settings on the thermostat. Leaving the thermostat set to AUTO, turn the temperature up high (80° F or higher) and see if the air conditioning fan continues to run. If it does, you’re likely dealing with issue #3 or #4. If the high-temp setting causes the air conditioner to shut off, then you may have insulation or cooling issues (reason #1). 

3. Call an HVAC professional

If your air conditioner fan won’t stop running and you’ve tried the recommended solutions above to fix it, we recommend contacting a local professional to come and assess the problem. We do not recommend trying to fix a broken thermostat or electrical issues without the help of a professional!

If you live in the Kansas City metro area, you can call A.B. May right now at 913-370-4898 or contact us online to schedule service.