Last Updated :April 2025
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:
- 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. - 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. - 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. - 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:
- 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. - 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 professional. - 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 services, 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 or request an appointment online.
This article is intended for general informational purposes only and may not be applicable to every situation. You are responsible for determining the proper course of action for your home and property. Aire Serv is not responsible for any damages that occur as a result of this blog content or your actions. For the most accurate guidance, contact the Aire Serv location nearest you for a comprehensive, on-site assessment.
FAQs About Air Conditioner Fan Troubleshooting
As an industry leader and a brand that is trusted by homeowners and businesses nationwide for our knowledge and experience, we’re happy to answer your HVAC questions. Here are answers to some of the frequently asked questions about why your AC fan keeps running.
How to turn the AC off?
Turning off your air conditioning is usually straightforward. Most systems have a clearly labeled "Power" or "On/Off" button on the thermostat—simply press this button! Some thermostats might display "Off" or a fan icon with a slash through it to indicate the system is no longer running.
For window units, the power is typically a sliding switch or a push button located on the unit itself. If you're unsure, consult your thermostat or unit manual. To conserve energy, remember to fully turn off the AC, not just adjust the temperature to a higher setting.
Why does the fan keep running on my air conditioner?
If your AC fan is still running when your thermostat is off, check your thermostat setting. It could be set to "On" instead of "Auto." In the "On" position, the fan runs continuously, regardless of whether the AC is actively cooling. Switching it to "Auto" ensures the fan only operates when the cooling cycle is active.
Another possibility is a delay feature found in some systems. After the cooling cycle ends, the fan might run for a short period to circulate any remaining cool air or to dry the evaporator coils, preventing mold growth. A faulty thermostat or a stuck relay could also cause the fan to run constantly.
If your AC is off and the fan is still running or another issue persists after checking your thermostat settings, consult an HVAC professional for AC repair services.
Why is my HVAC fan constantly running?
If your AC blower motor will not shut off, there might be one of several reasons:
- Thermostat mode: Double-check your thermostat setting. If it's set to "Fan On" instead of "Auto," the fan will run continuously for constant air circulation throughout your home, regardless of heating or cooling needs. Switching to "Auto" will make the fan cycle with the system.
- System settings: Some HVAC systems have user-configurable fan settings beyond "On" and "Auto." Check your thermostat or system control panel for options like continuous low-speed fan operation, which can improve air quality.
- Wiring problems: Faulty wiring between the thermostat and the HVAC unit can sometimes cause the fan to run constantly.
- Control board issues: A malfunctioning control board within your furnace or air handler could be sending a continuous signal to the fan motor.
- Emergency heat mode: In some systems, the fan runs continuously in emergency heat mode. Ensure this mode isn't accidentally activated.
Does the AC condenser fan always run?
No, the condenser fan in your AC unit should not run constantly. It's a key component of the outdoor condenser unit, and its primary job is to help dissipate heat from the refrigerant.
The condenser fan should only operate during the cooling cycle. When the thermostat calls for cooling, the compressor activates to circulate refrigerant. Simultaneously, the condenser fan turns on to blow air across the condenser coils, allowing heat to be released to the outside.
Once the desired temperature is reached, the compressor turns off, and the condenser fan should also stop running. If your condenser fan keeps running, even when the AC isn't actively cooling, it indicates a potential problem.
Does the HVAC fan run when the heat is on?
Yes, the HVAC fan typically runs when the heater does. When the thermostat calls for heat, the furnace ignites and warms the air. The HVAC fan then kicks in to distribute this warm air through the ductwork.
What does running the fan on the AC do?
Running the fan on your AC unit serves a couple of purposes, depending on whether the cooling is active or not.
- When the AC is actively cooling, the fan circulates the chilled air throughout your ductwork and into your rooms, effectively lowering the temperature. It works in tandem with the compressor and condenser to distribute the cooled air evenly.
- If you run the fan without the AC cooling, it essentially turns your HVAC system into a whole-house ventilation system. The system can help circulate air within your home, equalizing temperature differences between rooms and bringing in fresh air if your system has an intake. However, running just the fan without cooling won't lower the temperature and will still consume electricity.
What should I do if my air conditioner compressor won’t turn off?
If your air conditioner's compressor won't turn off, you may experience excessive cooling and waste energy. Here are some steps you can take:
- Check your thermostat: Ensure the thermostat is set to "Auto" and the desired temperature is a few degrees warmer than the current room temperature. If it's set to "Cool" and a very low temperature, the compressor will keep running.
- Inspect the contactor: The contactor is an electrical switch in the outdoor unit. A stuck contactor can keep the compressor running. However, do not attempt to manually manipulate it yourself, as there is a risk of electrical shock.
- Look for ice buildup: Excessive ice on the indoor or outdoor unit can sometimes cause the compressor to run continuously. If you see ice, turn off the entire system and allow it to thaw completely before restarting.
- Contact an HVAC professional: If the thermostat settings are correct and there's no obvious ice buildup, the issue likely involves a faulty contactor, a problem with the control board, or a refrigerant issue. Call a qualified HVAC service professional for diagnosis and repair to prevent further damage to your system.
