Why Does the Fan Keep Running on My Air Conditioner?

image of an air conditioner fan depicting a compressor fan not turning off

When the most common sound you hear in the summer is the drone of your air conditioner, it is time to admit that there is a problem. With the exception of switching your unit to run manually, an air conditioner should never run constantly. On the contrary, it needs to take regular breaks. A normal cycle should last between 15 and 20 minutes of run time, followed by an obvious pause before it repeats. Even units that regularly run for more than 20 minutes before taking a break are showing signs that there is a problem that needs to be addressed. This article answers the question, “Why does the fan keep running on my air conditioner?”.

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Why Does The Fan Keep Running On My Air Conditioner?

There are numerous possible causes for an air conditioner’s fan to keep running, including:

  • the fan is damaged
  • the thermostat is broken
  • there is a problem with the air filter
  • the fan switch was turned to “manual”
  • the condenser coils are dirty or frozen
  • too much hot air is getting into your home
  • the unit is not the right size for your house
  • the ductwork is old, broken, or otherwise problematic
  • there is not enough coolant/refrigerant in the air conditioner
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Cause #1: Damaged Air Conditioner Fan

image of an air conditioner compressing unit with a broken fan

For older cooling units, a damaged fan could be the reason it just will not stop. Normal wear and tear can affect this component over time, and debris or buildup near the motor will wear it down. Any excessive buildup will cause a fan to crack and break, but instead of making the unit stop, the opposite will happen — the unit will work that much harder to perform.

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Cause #2: Broken Thermostat

The thermostat is like the brain of the air conditioner — it tells the unit what its goal is and allows the system to take a break once that goal is met. However, a problem with the thermostat will throw off the entire process. It could be reading the indoor temperature incorrectly or not reading it at all and making your unit think that it has yet to meet its goal.

Related Article: How To Prevent Your Air Conditioner From Freezing Up

Cause #3: Problem With The HVAC Air Filter

image of a dirty air filter for home hvac system

Air filters stop dust, dirt, debris, and other particles from infiltrating your unit and ruining your air quality. Old, dirty air filters will not allow enough air through for the system to perform adequately. Therefore, it will be forced to run constantly. If the air filter seems clean or has just been changed, consider that it could be the wrong type of filter for the unit. Incorrect filters may be too restrictive for other units, which causes them to struggle and remain on.

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Cause #4: Fan Switch On Manual

Various units have different wording, but if your fan is switched to “on” or set to “manual,” then the air conditioner will not turn off until you turn it off by hand. Ensure the unit is on auto and see if it begins to run a normal cycle. A normal cycle runs 15–20 minutes before turning off for 5–15 minutes, depending on the size of the home, the weather,  and the unit itself. If the fan turns off for less than 5 minutes before kicking back on, you have a problem. Additionally, if the unit runs for less than 15 minutes each time it turns on, this is also a problem. In this case, the unit is too big for the home and is short-cycling, which wastes a lot of energy and does not dehumidify a home the way it is supposed to.

Related Article: Key Differences Between Central & Forced Air Systems

Cause #5: Dirty Or Frozen Air Conditioner Condenser Coils

HVAC technician working on controls of air conditioner

Air conditioners have condenser coils that fall victim to a build-up of dust, dirt, and debris, which can make your unit act up. The coils can also freeze up as a result of having too much refrigerant in the system, lines getting blocked, or outdoor temperatures plummeting. In either case, the result is an air conditioner that never turns off.

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Cause #6: Too Much Hot Air Getting In

If too much warm air is coming in and all the cold air is leaking out, your unit will have no choice but to run all the time to compensate for the loss. This means that it may not be the air conditioner that has the problem — it may be your home instead. Small holes, cracks, gaps around doors and windows, or a lack of insulation in the attic or throughout the house may be the culprit. 

Related Article: Why Are My Lights Flickering When My AC Turns On?

Cause #7: Wrong Size Air Conditioning Unit

Trying to cool a massive home with a tiny air conditioner will not work. Instead, the unit will run constantly as it tries to reach its indoor temperature goal, but will never succeed. You should only consider this as a potential cause if the unit is brand new and never turns off. Otherwise, you would have noticed the problem sooner.

Related Article: What is a High-Velocity Mini Duct HVAC System?

Cause #8: Trouble With The HVAC Ductwork

image of rattling ductwork

Particularly in older homes, cooling units may run excessively if there is a problem with the home’s ductwork. Over time, ductwork can start to break down and deteriorate, fall apart, or even cave in. This can cause a clog that greatly restricts airflow and forces an air conditioner to work harder than it should. Even ductwork that is not very old can have problems that cause leaks and allow the cool air to escape before it ever reaches the rooms in your home. Additionally, ductwork that lacks insulation will warm up the cool air before it gets into circulation.

Related Article: Is Your HVAC System Protected From Power Surges?

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Cause #9: Not Enough Air Conditioner Coolant

The cooling agent that runs through your air conditioner and lowers the temperature of hot air is known as coolant or refrigerant. Too much of it could cause a freeze within the unit, but not having enough of it will force the system to work overtime. 

Related Article: When to Call Emergency HVAC Services

Call A Professional HVAC Contractor

image of homeowner calling hvac company

Allowing a unit to keep working that hard will inevitably cause a breakdown in the entire system and will be much more expensive to remedy than whatever problem started the entire mess. In most cases, an air conditioner that never shuts off is a problem that can only be correctly diagnosed and properly fixed by an experienced HVAC professional.

Related Article: 10 Reasons Why Your AC Unit Isn’t Blowing Cool Air

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