When your AC unit won’t turn off, it’s more than just an annoyance—it’s a sign of a potential HVAC system issue. A continuously running air conditioning system can lead to higher energy bills, excessive wear on electrical components, and an overworked blower fan.
Left unchecked, it can cause damage to evaporator coils, the blower motor, and the condenser coils, reducing efficiency and lifespan. In this guide, we’ll walk you through common causes—from incorrect thermostat settings to a stuck relay switch—and provide practical fixes to restore the cooling cycle.
Whether it’s a simple thermostat fan setting adjustment or a professional air conditioner repair, we’ve got you covered.
Why Won’t My AC Turn Off?
If your AC won’t turn off, common causes include incorrect thermostat settings, a clogged air filter, frozen evaporator coils, dirty condenser coils, refrigerant leaks, or a faulty fan limit switch. To fix it, check airflow restrictions, adjust thermostat settings, clean the outdoor condenser unit, and schedule HVAC maintenance if the issue persists.
Common Causes of an AC That Won’t Turn Off
When your AC unit won’t turn off, it’s often due to incorrect thermostat settings, restricted airflow, refrigerant issues, electrical malfunctions, or duct leaks.
Below, we’ll break down each issue and provide step-by-step solutions to help you restore your system’s proper cooling cycle.
Thermostat Issues
A bad thermostat or incorrect thermostat settings can cause an air conditioning system to run continuously, even when the desired set temperature has been reached.
✖️ Common Causes:
- Incorrect thermostat temperature settings – The system doesn’t recognize the current temperature correctly.
- Thermostat stuck in “fan mode” – This makes only the system fan run non-stop.
- Loose wiring connections – A bad thermostat or faulty circuit board can disrupt proper cycling.
✅ How to Fix It:
- Check thermostat temperature settings – Make sure it’s set to “cool” and at an appropriate temperature.
- Adjust thermostat fan settings – Set to “auto” instead of “on” to prevent continuous operation.
- Replace batteries or reset the thermostat – Sometimes, a simple reset can resolve miscommunications.
- Inspect for loose wiring – If you notice inconsistencies in how the cooling unit responds, call an HVAC system technician to inspect the wiring.
- Upgrade to a programmable or smart thermostat – This helps regulate indoor air temperature more effectively.
If your air conditioner won’t turn off after these steps, thermostat replacement may be necessary.
Clogged or Dirty Air Filter
A clogged air filter restricts air flow, forcing the blower motor assembly to work harder to circulate cool air, leading to constant power usage.
✖️ Signs of a Dirty Air Filter:
- Weak airflow from vents
- Frozen evaporator coils
- Higher energy bills
- Overheating blower motor
✅ How to Fix It:
- Turn off the air conditioning system.
- Locate the air filter near the indoor unit or return vent.
- Check the filter’s condition – If it’s coated in dust, replace it immediately.
- Use a high-efficiency air filter to reduce airflow restrictions.
- Set reminders to replace your filter every 1-3 months.
A dirty blower fan can also contribute to airflow problems, so make sure fan blades are clean and free of dust. Regular filter changes prevent airflow restrictions, improve efficiency, and help maintain a proper cooling cycle.
Frozen Evaporator Coils
If your evaporator coils freeze, they won’t properly release heat, causing the air conditioner to run continuously without cooling effectively.
✖️ Signs of Frozen Evaporator Coils:
- Ice buildup on refrigerant lines
- Water leaks near the indoor unit
- Weak airflow from vents
✅ How to Fix It:
- Turn off the HVAC system immediately.
- Allow the ice to thaw – This can take several hours.
- Check for airflow restrictions – A clogged air filter or dirty blower fan could be causing the issue.
- Inspect refrigerant levels – Low refrigerant can cause frozen evaporator coils.
- Make sure the fan setting is on ‘auto’ to prevent excess moisture buildup.
- Schedule professional air conditioner repair if the coils freeze repeatedly.
A faulty fan limit switch, incorrect thermostat settings, or air flow restrictions can also contribute to coil freezing, so addressing these issues proactively prevents recurring problems.
Refrigerant Leaks or Low Refrigerant Levels
If your air conditioner won’t turn off but fails to circulate cool air, a refrigerant leak or low refrigerant levels might be the cause.
✖️ Signs of a Refrigerant Leak:
- Hissing or bubbling noises from refrigerant lines
- Warm air instead of cool air
- Higher electricity bills despite constant operation
✅ How to Fix It:
🚨 Only a licensed HVAC technician can safely handle refrigerant issues. However, you can:
- Inspect for leaks – Look for oily residue near the outdoor condenser unit or indoor unit.
- Check for frozen evaporator coils – A refrigerant issue can cause the coils to freeze.
- Ensure correct fan settings – Adjust thermostat fan settings to maintain airflow.
- Schedule a professional recharge – HVAC professionals will test for leaks and replenish refrigerant levels.
Since EPA regulations prohibit DIY refrigerant refills, it’s crucial to get professional air conditioner repair to prevent long-term compressor contactor damage.
Leaky or Poorly Insulated Ductwork
Leaky air ducts force the HVAC system to work harder, making it seem like your AC unit won’t turn off.
✖️ Signs of Duct Leaks:
- Uneven cool air distribution
- High energy bills
- Fan blowing constantly, even when the system should be off
✅ How to Fix It:
- Check for visible gaps in the ductwork, especially near vents.
- Feel for escaping air around duct joints.
- Use temporary duct tape for minor leaks.
- Schedule a duct inspection – A technician can seal major leaks and add insulation.
Leaky ductwork wastes heating energy and overworks the cooling system, causing your blower fan and fan motor to run continuously. Proper duct sealing helps maintain efficient cooling cycles.
Oversized AC Unit
An oversized cooling unit cools the air too quickly, failing to regulate humidity levels and causing the air conditioner to run inefficiently.
✖️ How to Know if Your AC Is Oversized:
- The AC fan runs constantly, but indoor air still feels humid.
- The system short cycles, turning on and off too frequently.
✅ How to Fix It:
- Adjust the fan speed – Low fan speed can help balance humidity removal.
- Increase insulation to reduce temperature fluctuations.
- Use a dehumidifier to manage excess moisture.
- Consult an HVAC technician about downsizing the unit.
A properly sized air conditioning unit ensures correct fan settings, consistent cooling cycles, and optimal indoor air comfort.
Electrical or Relay Issues
A stuck relay switch, faulty fan limit switch, or bad electrical wiring can prevent an air conditioning unit from turning off.
✖️ Signs of Electrical Problems:
- Buzzing or clicking sounds from the circuit board
- The AC unit won’t turn off even after adjusting the thermostat settings
- Warm air blows when cooling should be active
✅ How to Fix It:
🚨 Electrical problems require professional repair due to safety risks.
- Turn off electrical power to the system at the breaker.
- Check for burnt or loose wiring connections.
- Call an HVAC technician to inspect the compressor contactor, faulty fan limit switch, and stuck relay switch.
Ignoring electrical power issues can damage the system fan, heating system, and blower motor, leading to costly air conditioner repair.
📖 Related Reading: Common HVAC Electrical Problems Every Homeowner Should Know
When to Call a Professional
While some AC issues can be resolved with simple thermostat adjustments or air filter replacements, certain problems require professional HVAC repair. Call an expert if:
- Your AC won’t turn off even after adjusting thermostat settings.
- Electrical issues occur, such as buzzing sounds, flickering power, or capacitor failures.
- Refrigerant leaks are suspected—signs include hissing noises and warm air instead of cool air.
- Frozen evaporator coils keep returning, despite replacing clogged air filters.
Ignoring these warning signs can lead to costly air conditioner repairs or complete system failure. HVAC professionals have the tools to diagnose faulty components, test refrigerant levels, and inspect electrical wiring safely, ensuring your cooling system runs efficiently.
Preventative Maintenance Tips
Keeping your air conditioning system in top shape prevents costly air conditioner repairs and extends its lifespan. Follow these preventive maintenance tips to ensure efficient operation:
✅ Schedule annual HVAC tune-ups to check for faulty components, refrigerant levels, and airflow restrictions.
✅ Keep vents unblocked to allow cool air to circulate freely and prevent strain on the blower motor.
✅ Use a smart thermostat to optimize cooling cycles and prevent unnecessary constant power usage.
✅ Clean the outdoor condenser unit regularly to remove dirt, leaves, and debris that could clog condenser coils.
Regular maintenance reduces electrical power failures, stuck relay switch issues, and fan speed inefficiencies, keeping your cooling system running smoothly year-round.
Conclusion
A continuously running AC can be caused by minor issues like a clogged air filter or incorrect thermostat settings, or major problems such as refrigerant leaks, frozen evaporator coils, or electrical malfunctions. Addressing these problems early can prevent system strain, reduce energy costs, and avoid expensive repairs.
If simple fixes like adjusting thermostat settings, replacing air filters, or cleaning condenser coils don’t resolve the issue, it’s time to call a professional.
If you're in the Pensacola area, schedule an inspection with Air & Energy of NWFL for expert HVAC service and reliable AC repairs you can trust!
This article was written by:
Co-founder and Home Comfort Specialist