How To Look At A House

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What is short cycling of an air conditioner or heat pump?

Monday, August 21, 2023

Short cycling of an air conditioner or heat pump is when the system turns on and off too frequently. A normal operating cycle is 15 to 20 minutes, then off for around 10 minutes. If the system turns off after just a few seconds or minutes, something is wrong. Because the life of the system is measured in on/off cylces, short cycling reduces the lifespan—besides being annoying.

    There are multiple possible causes, and determining which one is the problem may require a visit from an a/c service tech:

1) Extremely dirty air filter - will drastically reduce the air flow over the evaporator coils in the air handler. They won’t be able to absorb in the heat adequately, causing the coils to freeze over and shut off the system prematurely. 

2) Improperly sized system - If the correct size for the a/c system is 2.5-tons, but the homeowner replaces it with a 4-ton unit, it will cool the house too quickly and shut off after just a few minutes. Air conditioning systems do two things to make a house interior comfortable: cooling and dehumidification. Dehumidication requires a substantial amount of air to flow over the evaporator coils in the air handler, to remove the humidity and drain the condensate water away. An oversize unit short cycles, leaving the air cooler but still humid.

3) Dirt/dust clogged evaporator coils in the air handler - will also also cause the evaporator coils to freeze over and shut down the system early. This is usually caused by a missing or damaged air filter.

4) A malfunctioning thermostat - can shut off the system too soon.

5) Low refrigerant level due to leakage - can cause ice formation on the suction line near the condenser and make the unit short cycle.

6) A failing, older compressor - can cause short cycling problems.

7) Bad capacitor - Most air conditioners and heat pumps have two capacitors: a start capacitor that provides an extra surge of electricity to overcome inertia and start the compressor moving, and a run capacitor that keeps it running once it has started. If the run capacitor is damaged, or if the flow of electricity to it is interrupted by a wiring problem, it may shut down the system—only to turn it back on again once the temperature hits a certain point.

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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at for $19.95.
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  To learn more about heating and air conditioning systems, see these other blog posts:

How can I find out the SEER of my air conditioner? 

My air conditioner won't turn on. What's wrong? 

How can I find out the size of my air conditioner? 

How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

Where is the air filter for my central air conditioner and furnace? I can’t find it? 

Does an old air conditioner use more electricity as it ages? 

How did homes stay cool in Florida before air conditioning? 

What is wrong with an air conditioner when the air flow out of the vents is low?

Why has the thermostat screen gone blank? 

Why does it take so long to cool a house when an air conditioner has been off for a while? 

Why is my air conditioner not cooling enough? 

What are the most common problems with wall/window air conditioners?  

Will closing doors reduce my heating and cooling costs? 

     Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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