Why Your AC Won’t Turn Off: Common Causes and Fixes

Most of the time, we worry about our AC units not turning on when they’re being pushed to the limit on sweltering summer days. But what if the problem is the opposite – your AC won’t turn off? This can be just as frustrating and costly. HVAC.com discusses common causes of this issue and steps to fix it.

Should an Air Conditioner Run Constantly?

An air conditioner should not run constantly. It typically runs about two to three cycles per hour that last about 15 minutes each. When the temperature on your thermostat is reached, the system should cycle off.

If your air conditioner continues to operate without turning off, contact a professional HVAC contractor to inspect and repair the system as needed. An AC that runs constantly will cause energy costs to skyrocket, increase wear and tear, and may lead to premature replacement.

Reasons Your AC Might Not Shut Off

Wrong Thermostat Setting

Sometimes the reason your AC won’t turn off is as simple as a wrong thermostat setting. It’s possible that someone bumped into the thermostat and caused the setting to drop under 70 degrees, perhaps to 65 or lower. This can make it appear as though the AC is running constantly, especially on extremely hot days, as it struggles to reach the set temperature.

Solution: Adjust the thermostat to the appropriate setting.

Thermostat Is Set to “On,” not “Auto”

If the thermostat is set to “on” instead of “auto,” the fan will continue to run even when the compressor is off, making it seem as if the air conditioner is operating all of the time. Setting your thermostat to “auto” will result in lower energy bills. However, some homeowners prefer to keep their thermostat fan on constantly for improved air circulation and air filtration.

Solution: Consider setting the thermostat to “auto” to ensure the fan runs only when the AC is on or leave it on “on” if you prefer constant fan operation.

Malfunctioning Thermostat

If the thermostat is malfunctioning or not calibrated correctly, it may fail to signal the AC to turn off even when the desired temperature is reached. This can lead to excessive energy consumption and increased wear and tear on the system.

Thermostats should generally be replaced about every 10 years. Over time, dirty sensors and damaged electrical wiring and connections can interfere with proper communication between your HVAC system and thermostat.

Solution: Contact an HVAC contractor to inspect the thermostat and determine whether it needs repair or replacement.

Electrical Problems

Electrical issues can cause an AC unit to run continuously by disrupting the signals between the thermostat and the system’s control components. For example, a faulty contactor or damaged wiring might prevent the system from receiving the proper signals to turn off, leading to constant operation. The control board, which manages various functions of the AC unit, might also be defective or malfunctioning, affecting its ability to turn off.

Solution: If you suspect an electrical issue with your air conditioner, reach out to an HVAC company as soon as possible.

Low Refrigerant

Low refrigerant levels may result in inefficient cooling and force the system to work harder, causing your AC to run continuously as it struggles to reach the thermostat’s set temperature. Refrigerant is an essential part of the cooling process as it absorbs and releases heat as it circulates through the system, enabling the cooling process.

Solution: Contact a professional to recharge the refrigerant and repair the cause of the leak.

Clogged Air Filter

Every air conditioning system includes an air filter designed to capture particles and contaminants before they enter the unit. When the filter becomes clogged, it restricts airflow, causing the air conditioner to work harder and potentially run longer cycles to reach the desired temperature. This can also make it appear your air conditioner won’t turn off. Check your filter monthly and change it every 2-3 months or according to the manufacturer’s guidelines.

Solution: Replace your air filter with a new one.

Undersized Air Conditioner

If your air conditioner is too small, it will struggle to efficiently cool your home, causing it to longer cycles or not shut off at all in an effort to cool your home. The only fix for an undersized air conditioner is buying the appropriately sized unit.

Solution: Contact an HVAC contractor to check if an undersized system is preventing your AC from turning off. If it is, you’ll need to buy a new system.

Dirty Condenser Coil

The condenser coil in your air conditioner’s outdoor unit is responsible for releasing heat. When this coil becomes clogged with dirt and debris, it can’t release heat effectively, causing the AC to run continuously and struggle to keep your home at a comfortable temperature. Additionally, blockages around the outdoor unit can restrict airflow, making the problem worse by hindering proper heat dissipation.

Solution: Clean the condenser coil yourself or hire a professional. If you’re not familiar with the ins and outs of HVAC systems, the latter is probably your best option.

Faulty Fan Limit Switch

A faulty fan limit switch can cause an AC to run continuously by failing to signal the system to turn off when the desired temperature is reached. This malfunction keeps the fan operating even when cooling is not needed.

Solution: Replace the faulty fan limit switch to help your AC cycle properly and turn off at the right temperature.

Regular Maintenance Can Limit Issues with Your AC

Many of the aforementioned issues that can lead to an air conditioner not turning off can be prevented with regular maintenance. An AC inspection and tune-up is recommended once a year, typically in the spring before you start using the system on a regular basis. Aside from adjusting, lubricating, and cleaning all necessary components, a technician can also spot issues before they lead to bigger, more serious problems that can prevent your system from starting or stopping.