AC Short Cycling

A short cycling AC can lead to decreased comfort and high energy bills. Learn more about the problem, its causes, and what to do.

When your AC is short cycling, that means that it is turning on and off again in an abnormal run cycle. It shuts off before it completes the cooling cycle. A properly sized and operating system may only run for 3 to 5 minutes and be off for hours in mild conditions at the start of the season, or it may run for hours with very short off cycles on hotter days. 

In contrast, a short cycling air conditioner may turn on and turn off frequently and so quickly that it doesn’t properly remove the humidity from the air, resulting in a cold and clammy feeling. You may also notice uneven cooling.

In addition to causing you discomfort, AC short cycling can result in higher energy bills (AC units use a lot of energy each time they start) and the increased wear and tear can mean rising AC repair costs.

If you’re wondering “Why is my AC short cycling?” there are two main causes: thermostat issues or an improperly sized system.

If you have a short-cycling AC unit, you need to consult with an HVAC professional to get to the root of the problem. There will be a different solution for each cause of your short cycling issues.

A malfunctioning thermostat can send the wrong signals to your HVAC system, telling it to start or stop cooling your home at random times. Try thermostat troubleshooting to resolve the issue.

A thermostat mounted in the wrong location can also cause problems. A thermostat mounted where it is exposed to direct sunlight can turn on the air conditioning, regardless of what the temperature is in the rest of the house or even the next room.

Your thermostat should be installed in a central location, away from registers and heat-generating appliances, and out of direct sunlight. Sometimes moving an improperly placed thermostat can resolve short-cycling.

An improperly sized air conditioner can suffer from short cycling from the day it’s installed. Specifically, an oversized system will reach the set temperature too quickly and will shut off before the cycle is complete. This short cycling can result in decreased humidity control, decreased comfort, and increased utility bills.

An oversized system results from the HVAC installer failing to do proper HVAC sizing calculations and just using square footage as a guide, or replacing an existing unit with the same size unit without doing a load calculation.

Unfortunately, the only way to resolve short cycling from an oversized system is to replace the system with a correctly sized system.

Keep your central air conditioning system running at peak performance with regular air conditioner maintenance. This includes changing the air filter every 1-3 months. Refer to our HVAC filter maintenance guide for some tips.

In addition, schedule yearly professional maintenance. Consider signing up for an HVAC service plan with your HVAC company. They’ll contact you to schedule a visit. Most HVAC service plans include an AC tune-up in the spring and a furnace tune-up in the fall.

You may also be eligible for discounts or preferred scheduling as a valued customer. Regular maintenance can help identify small problems and keep them from becoming big ones.

Finally, consider opting into Trane Diagnostics. This allows your Trane dealer to monitor your system remotely. They’ll receive alerts of any issues with your system and can act quickly to help you, even when you’re away from home on vacation.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

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