When outdoor temperatures are higher than usual, your air conditioner may cycle a bit longer than it does during milder weather. However, your air conditioner should not run constantly. A cooling cycle should last approximately 15 to 20 minutes and typically runs about two to three cycles per hour. When the temperature on your thermostat is reached, the system should cycle off. If your cooling unit is running longer, something is wrong within your HVAC system and repair services are needed.
If your air conditioner is running constantly, it will cause energy costs to increase, more wear and tear, leading to inefficient performance and defects that cause breakdowns. Damaged parts will need to be replaced, increasing your repair costs.
Possible Causes of AC Not Turning Off with Solutions
- Faulty Thermostat
Check to see if the thermostat is set to the right air conditioning temperature setting. If the thermostat is set to a cold standard that is far too low, then your air conditioner won’t shut off because it’ll be working constantly toward a temperature it can’t reach.
Solution: Turn up the temperature so the thermostat is set a few degrees higher than the current room temperature. This should cause the thermostat to communicate with the air conditioner to end its cycle. You can also change the fan setting. Sometimes it’s only the system fan running and not the air conditioner. Make sure the thermostat is programmed to AUTO for the fan setting so the fan will not run in between cooling cycles. Now, if the air conditioner still won’t turn off, you know it’s an issue.
Over time, a thermostat can lose accuracy and experience damage that disrupts communication with cooling and HVAC equipment. Dust and dirt build-up on temperature sensors make it difficult for the thermostat to detect the temperature of the room. Wiring damage and loose electrical connections interfere with signals sent between the thermostat and air conditioner, which can cause the cooling system to run longer than necessary.
2. Frozen or Dirty Coils
Condenser coils are essential within the AC system. They remove the heat from the air. If they get dirty, the layer of dirt or debris causes them to overwork themselves and operate inefficiently. This keeps the air conditioner from reaching the set cooling temperature and can prevent your system from shutting off.
A dirty evaporator coil will weaken your central AC's ability to effectively cool your home. The decrease in efficiency will make it work harder and run longer to achieve your desired indoor temperature. A frozen evaporator coil can also make your AC unit run constantly, potentially causing equipment damage and exposing your home to water damage. Reduced air flow is one possible cause of a frozen evaporator coil.
Solution: Inspect your condenser and evaporator coils to see if they need to be wiped down. Because most modern AC units have tightly sealed evaporator coils, call an HVAC expert for servicing.
- Air Flow Problems
Air flow blockages can force your air conditioner to work overtime. When your air filter becomes clogged, it restricts airflow, causing the air conditioner to work harder and potentially run longer cycles to reach the desired temperature. A faulty blower fan can also reduce the performance of your AC system and force it to run constantly. One of the most common problems is dust and dirt accumulation on the blower fan.
Solution: Inspect and change a dirty air filter, open room vents that are shut or covered, clear away debris that has gathered on the condenser unit and check for leaky air ducts and other ductwork problems. Cleaning and lubricating the blower assembly will improve the performance and efficiency of your system. This should be done as part of your annual maintenance to prevent future problems from popping up.
- Stuck Fan Limit Switch
The fan of your air conditioning unit turns on when instructed by the thermostat. But it can also do so as part of an independent air circulation process. This is made possible by the presence of a fan limit switch. The fan limit switch overrides any thermostat signal telling it to stop running so that it can keep going. If the switch sticks closed, the fan receives power all the time and continues blowing for hours, during and in between cooling cycles.
Solution: Check whether you need to switch the fan limit switch from manual to automatic. You may need to replace the faulty fan limit switch to help your AC cycle properly and turn off at the right temperature.
- 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 expert as soon as possible.
- Incorrectly Sized AC Unit
Properly sizing an air conditioning system is essential to its performance, efficiency and longevity. A system that is too small will run constantly, leading to inefficient performance, excessive wear and premature failure. A system that is too large will cycle on and off frequently, reducing its efficiency, creating hot and cold spots between cycles, and preventing it from running long enough to properly dehumidify your home.
Solution: Skilled AC experts will size the system based on the size of the home, the number of rooms, the layout, room occupancy, the number of windows, the quality of insulation, and many other factors. This results in an efficient, long-lasting system that improves comfort and minimizes cooling costs.
At the end of the day, the only way to avoid big, unexpected problems with your AC is to be proactive with regular maintenance. Regularly clean your outdoor units (once a month) and make sure your home is equipped with proper insulation and ventilation to help prevent an AC shutdown.
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, an HVAC expert can also spot issues before they lead to bigger, more serious problems that can prevent your system from starting or stopping.
If your air conditioner won’t shut off, your local Lennox pro can resolve the problem by cleaning the condenser coils, replacing dirty air filters and checking for electrical issues. If you have noticed that your air conditioner won’t shut off, call a professional for servicing.
This has been reviewed by Nick Orth, Director of Outdoor Cooling, for accuracy. Nick brings 20 years of expertise in the HVAC space.
