Why Your Air Conditioner Fan Keeps Running: Common Causes and Fixes

air conditioner condenser fan close up

As the hum of your air conditioner becomes the soundtrack of your summer, it’s clear there’s an issue to address. A properly functioning air conditioner shouldn’t operate non-stop but should cycle off periodically. Ideally, each cycle involves 15 to 20 minutes of operation, followed by a noticeable rest period of roughly 7-10 minutes. If your unit persistently operates longer than 20 minutes without pausing, this signals an underlying problem that requires attention. This article from R.F. Ohl answers a common 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

Several factors might cause your air conditioner’s fan to keep running without stopping. These include:

  • Damage to the fan itself
  • A malfunctioning thermostat
  • An issue with the air filter
  • The fan switch is set to “manual”
  • Dirty or frozen condenser coils
  • Excessive hot air entering your home
  • An improperly sized unit for your home
  • Aged, damaged, or problematic ductwork
  • Insufficient coolant/refrigerant levels in the system

Reason #1: Faulty Air Conditioner Fan

faulty and old air conditioner fan

In older air conditioning systems, a faulty fan is often the culprit behind non-stop operation. Normal wear and tear over time can compromise this component. Accumulation of debris or buildup around the motor exacerbates its deterioration. Such excessive buildup can lead to the fan cracking and breaking. Rather than causing the unit to shut down, this damage results in the air conditioner working overtime to maintain performance.

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Reason #2: Malfunctioning Thermostat

The thermostat serves as the air conditioner’s command center, dictating the unit’s operational objectives and signaling when it can rest upon achieving those goals. If the thermostat malfunctions, it disrupts this critical process. It might misread the indoor temperature or fail to read it entirely, causing the unit to operate continuously under the mistaken belief that it has yet to reach its intended target.

Reason #3: Issues with the HVAC Air Filter

faulty and old air conditioner fan

Air filters prevent dust, dirt, debris, and other particles from entering your unit and compromising indoor air quality. When filters become old or clogged, they restrict airflow, forcing the system to operate incessantly to meet cooling demands. Additionally, if the air filter appears clean or has recently been replaced, it might still be the wrong type for your system. Inappropriately matched filters can be too restrictive, causing the unit to overwork and continuously run.

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Reason #4: Fan Switch Set to Manual

Air conditioning units may vary in settings, but if the fan switch is turned to “on” or “manual,” the unit will continue running until manually shut off. To test this, switch your unit to “auto” and observe if it resumes a normal operation cycle. A standard cycle should last between 15 and 20 minutes, followed by a downtime of 5 to 15 minutes, which can vary based on your home’s size, the current weather, and the unit itself. 

Issues arise if the fan turns off for less than 5 minutes before restarting or runs for less than 15 minutes each cycle. This indicates the unit is oversized for your home, leading to short-cycling. Short cycling not only wastes energy but also fails to dehumidify the space properly.

Reason #5: Compromised Air Conditioner Condenser Coils

air conditioner coil

Condenser coils in air conditioners are prone to accumulating dust, dirt, and debris, leading to operational difficulties. Additionally, these coils can freeze due to excessive refrigerant, blockages in the system, or significantly low outdoor temperatures. In both scenarios, the coils cause the air conditioner to continue running non-stop.

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Reason #6: Excessive Hot Air Infiltration

When too much warm air enters your home while the cooled air escapes, your air conditioner is forced to operate continuously to compensate for the loss. This indicates that the problem might not lie with the air conditioner itself but with your home’s structure. Small openings, cracks, gaps around doors and windows, and insufficient insulation in the attic or other areas of the house, could be responsible for this inefficiency.

Reason #7: Incorrectly Sized Air Conditioning Unit

Using a small air conditioner to cool a large home is ineffective; the unit will operate incessantly in an attempt to achieve the set indoor temperature but will continually fail to do so. This issue should primarily be suspected if the unit is new and needs to turn on. If the unit had been improperly sized from the start, the problem would have been apparent much earlier.

Reason #8: Issues with HVAC Ductwork

In older homes especially, the continuous operation of cooling units may be due to problematic ductwork. Ducts can deteriorate, break down, or collapse over time, leading to clogs that severely restrict airflow and force the air conditioner to overwork. 

Even relatively new ductwork can have faults that result in leaks, allowing cool air to escape before it reaches its intended destination within the home. Furthermore, ductwork lacking adequate insulation can cause the cool air to warm up prematurely, hindering effective distribution throughout the house.

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Reason #9: Insufficient Air Conditioner Coolant

tools for checking and refilling air conditioner refrigerant

Coolant, or refrigerant, is the substance that circulates through your air conditioner to cool down the hot air. While an excess of coolant can lead to freezing within the system, a lack of sufficient coolant will cause the air conditioner to run continuously as it struggles to lower the temperature effectively.

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Contact a Professional HVAC Contractor

Permitting an air conditioner to operate excessively can cause a complete system breakdown, resulting in repairs that are far costlier than addressing the initial issue. In most instances, an air conditioner that fails to shut off indicates a problem that requires accurate diagnosis and effective resolution by a skilled HVAC professional.

Air Conditioner Fan FAQs

FAQ written on sticky note beside magnifying glass focusing on question mark

Here are some frequently asked questions about air conditioner fan issues to help you understand common problems and solutions.

Is It Possible for an Air Conditioner to Run Constantly Due to Insufficient Coolant/Refrigerant?

Yes, if your air conditioner has low coolant or refrigerant levels, it may operate continuously. The system must work harder to cool your home, leading to non-stop fan operation. It’s crucial to check for leaks, repair them, and replenish the coolant to ensure your system operates efficiently and to avoid further issues.

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Why Does the Fan Keep Running on My Air Conditioner?

The continuous operation of your air conditioner’s fan could signal several problems, including damaged components, thermostat malfunctions, clogged air filters, or the fan setting being left on manual. Addressing these issues promptly is crucial for maintaining system efficiency and preventing further damage.

How Do I Know If My Air Conditioner’s Fan Is Damaged?

photo of clueless man with arms and hands raised not knowing if AC fan is damaged

Indications of a damaged fan in your air conditioner include unusual noises during operation, a decrease in airflow, or the fan consistently running without cycling off. Fans in older cooling units are especially prone to damage from wear and tear or debris buildup around the motor.

Can a Broken Thermostat Cause the Air Conditioner’s Fan to Run Constantly?

Yes, a malfunctioning thermostat can cause your air conditioner’s fan to run non-stop. This occurs because the thermostat might inaccurately gauge indoor temperatures or fail to signal the air conditioner to shut off, thus preventing the system from cycling off upon reaching the set temperature.

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When Should I Seek Professional Assistance for My Air Conditioner’s Constant Fan Operation?

If your air conditioner’s fan won’t stop running, it’s wise to seek professional help. Continuous operation can indicate various underlying problems that need expert diagnosis and repair. Contacting a skilled HVAC contractor can ensure that the root causes are identified and corrected, restoring your system’s efficiency and performance.


If your air conditioner’s fan runs continuously, it may indicate issues ranging from damaged fans and malfunctioning thermostats to inadequate coolant levels or improper unit size. Understanding these common problems helps effectively address and prevent extensive damage to your system. Regular tune-ups and timely repairs are vital to ensure your air conditioning unit functions efficiently and lasts longer. If you’re experiencing persistent issues, consulting a professional is essential to diagnose and resolve underlying problems effectively, ensuring your home remains comfortable and energy-efficient.

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R.F. Ohl is a premier provider of heating and cooling services in Northeastern Pennsylvania, featuring a team of highly skilled, certified technicians ready to handle HVAC tune-ups, repairs, installations, and replacements. We’re committed to delivering superior service to every customer.

At R.F. Ohl, we recognize the importance of a comfortable, energy-efficient home, offering competitive pricing on all services. Our maintenance services can boost comfort and lower energy costs. If you need HVAC repair or replacement, our expert technicians will guide you to the best solutions within your budget. We guarantee your satisfaction with our work.

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