A central AC system typically cycles on two to three times per hour. When an AC cycles on and off more frequently, it’s short cycling. Short cycling causes higher electricity usage and increased wear and tear. It may also indicate a serious underlying problem.
Heat Waves
ACs and heat pumps have to work harder to reach a temperature than to maintain it. On a normal day, you can expect your AC to cool your home by two to three degrees an hour. When the temperature is 100 degrees Fahrenheit or more, cooling by one to two degrees an hour is common. During heat waves, you may notice longer cycles. A typical AC cycle is 10-15 minutes, but 20 minutes isn’t unusual during very hot weather. Still, your AC shouldn’t turn on and off more frequently just because it’s hotter outside.
Oversized AC Unit
If a new AC short cycles, it may be that it’s too big for the home. Professional installers size ACs based on the precise cooling output needed. An optimal cooling output keeps a home comfortable while optimizing energy efficiency and minimizing total costs. If an AC puts out excessive cooling, the living space will reach the desired temperature too quickly.
That will cause it to turn on and off more often than is healthy for the equipment. One option is to replace the oversized AC. Another is to upgrade to HVAC zoning. An installer may be able to solve the sizing issue through upgrades like a smart thermostat, a variable-speed blower, duct dampers, and additional ductwork.
Electrical Issues
Electrical problems are a common cause of AC short cycling. A bad relay can cause this behavior. Deteriorated wiring can cause intermittent power losses. Corroded electrical connections can lead to power fluctuations. It may also be that your outdoor compressor unit has a bad capacitor that needs replacement.
Clogged Filter
Restricted airflow reduces AC efficiency and can cause overheating if the pressure is too high. The most common cause of this is a filter that’s clogged and needs replacement. It can occur if you use a filter with a higher MERV rating than your system supports. Less commonly, it can also be due to excessive dust accumulation in your ducts.
Dirty Coils
Heat pumps and ACs have two coils that can build up grime over time. This is among the top reasons that seasonal cooling maintenance is so important. The grime is an insulator, which inhibits the coils from absorbing and releasing heat efficiently. This problem can worsen to the point of overheating. The system shuts down as a protective measure and then cycles on again once it’s cooled.
Thermostat Malfunctions
You generally can’t cause short cycling through incorrect settings or programming. That said, faulty thermostat control can cause it. In some cases, the underlying issue may be as simple as dirty contacts or low batteries. Incorrect thermostat placement can cause this issue. For example, a thermostat placed in direct sunlight may register a higher temperature than the rest of the home, causing the AC to cycle incorrectly. It may also be that the thermostat is simply getting old and needs replacing. Modern thermostats often have components that deteriorate over time, such as thermistors, discs, and springs.
Frozen Evaporator Coil
The evaporator coil is what absorbs heat energy from the air into the refrigerant. If the coil freezes, absorption happens less efficiently or not at all. That causes the system to overheat and cycle irregularly. A frozen coil is often a symptom of another issue, such as a clogged filter or the blower running at a low speed. If you have a split AC system, which is typical, the evaporator coil will be indoors, such as in the attic. If you have a packaged system, it will be in the outdoor cabinet.
Low Refrigerant Pressure
Micro-leaks are the most common type of refrigerant leaks. They often don’t cause sudden failure but rather performance issues that worsen over time. You’ll often notice other symptoms, including high electric bills, before you get to the point where your system overheats and short cycles.
Local AC Services in the Greater Portland Area
Bean's Heating & Air is a trusted and local HVAC company based in Portland, ME. Our AC repair technicians are available seven days a week, ready to diagnose and resolve your cooling issues. We repair all AC brands and models and use only the highest-quality products and materials. If you’re experiencing AC short cycling, call today or contact us online to schedule an AC appointment.
