What Is Short Cycling and Why Is It Bad for My HVAC System?

Short cycling, which is when your HVAC system turns on and off too frequently, is a common problem. It can be harmful to your heating and cooling system and signal a variety of issues. Some of these can require air conditioning repair, so you don’t want to ignore a unit that has short cycles. 

At Trio Heating & Air, our licensed technicians can quickly diagnose the underlying issue and provide any repair necessary. We recommend scheduling service before the damage adds up and leads to more costly repairs. But let’s explain the issue further to help you understand its scope and causes.

What Is Short Cycling?

An HVAC system runs for a time, then turns off before turning on again if your thermostat is in “Auto” mode. One on/off period is called a “cycle”. It should last from 20 to 30 minutes, so your heating or cooling unit cycles two to three times per hour. 

The system should turn off when the set temperature is reached. While actual cycle times can vary depending on your system and home, problems can occur if your HVAC unit runs too briefly. If it does, this is called short cycling. It can cause the system to use more power, increase your utility bill, and limit cooling or heating performance.

Short cycling occurs most often with single-stage systems. They only turn on and off, so an AC runs at full blast every time it’s too warm. Two-stage systems have more flexibility to adjust to conditions, while variable-speed ACs and furnaces run at incremental power levels, eliminating the need for cycling. They can stay on all the time but use less energy.

Can Short Cycling Damage My HVAC System?

When an HVAC unit short cycles, it turns on and off again repeatedly in quick intervals. The compressor continuously starts up and shuts down. This not only wastes energy but also overworks the system. Parts of the compressor can wear out quickly. Or, the compressor can overheat and burn out, leading to one of the most costly AC repairs.

The constant starting and stopping can also accelerate wear on other components. This means you may eventually deal with more frequent repairs. Addressing the issue can avoid needing another repair shortly after your HVAC unit is fixed.

Reasons Your HVAC System Can Short Cycle 

One or more issues can cause your cooling and heating system to short cycle. Therefore, short cycling can signal that there are multiple issues with your HVAC system. Here are some reasons the unit won’t stay on long enough.

  • Dirty Filter: Air filters should be changed at least once every three months (or sooner). Otherwise, they can become clogged with dust, dirt, pet dander, particles from cooking smoke, and other contaminants. A dirty filter can cause your HVAC unit to short cycle because limited airflow makes things warmer, causing the system to overheat and shut down.
  • Frozen Coils: Short cycling is one of the effects of faulty AC coils. A coil can freeze simply because it’s too cold outside. However, it can also be due to restricted airflow or a refrigerant leak. If a coil freezes once, turn the unit off to thaw it out. If it freezes repeatedly, call a professional.
  • Refrigerant Leak: A leak in a refrigerant line can prevent your HVAC system from drawing heat out of your home. Topping off refrigerant has a limited effect because it circulates in a closed loop. You should never need to add any. This means there’s a leak, and your AC can become overworked and shut off. 
  • Leaky Air Duct: Short cycling can also be caused by a leaky air duct. Metal ductwork can corrode and develop holes over time; duct sections can also become disconnected. If you have air ducts with a metal coil supporting an insulated plastic wrap, the outer wrap can break down and crack over time. Any duct leak can cause conditioned air to escape and untreated air to enter, forcing your heating or cooling unit to work harder.
  • Faulty Thermostat: An aging thermostat can malfunction and cause your HVAC unit to turn on and off unexpectedly. It may have an analog dial or slider that’s not as accurate, causing performance issues. But even if you install a digital or programmable thermostat, placement is always a factor. If the unit is in direct sunlight, near a draft, or close to a heat-generating appliance, it can send the wrong signals to your HVAC system.
  • Electrical Problem: An electrical issue, such as one originating in the thermostat or with one of its connections, or a malfunctioning capacitor, fuse, or circuit board, can also cause an AC or furnace to short cycle. Bad wiring can also be a factor. 
  • Oversized HVAC Unit: If the system is oversized, it can reach the set temperature too quickly. The thermostat then shuts the unit off. Conditioned air may barely reach other rooms before the system turns back on. Therefore, your HVAC system has short cycles and the only solution is to modify or replace it.

You’ll save time and money by planning for installation with a Manual J load calculation. It helps your local HVAC contractor properly size your new system. Short cycling and other issues can be avoided.

How Do I Know My AC/Heater Is Short Cycling?

If you notice your cooling or heating system turning on and off every five to ten minutes, it is short cycling. It isn’t always an obvious issue, especially if your HVAC system is relatively quiet or its familiar sound blends in with background noises. Subtle signs include a slight decrease in cooling or heating performance. Increased humidity, which can make your home quite uncomfortable, is another sign your AC isn’t running long enough. 

Can Short Cycling Be Prevented?

Short cycling can be bad for your HVAC system. However, it can be prevented and there are solutions to address it, including the following:

  • Schedule regular maintenance with your local HVAC contractor.
  • Change the air filter as recommended.
  • Have a professional check the low-pressure control switch.
  • Relocate the thermostat to an open room.
  • Install a portable or whole-home dehumidifier.
  • Properly seal leaky air ducts.
  • Install an HVAC system that allows zoning.

Contact Trio Heating & Air

If your HVAC system is short cycling, our licensed technicians can determine why and perform the appropriate adjustments or repairs. We not only ensure your satisfaction but also the optimal performance and efficiency of your AC or furnace. The goal is to find the best solution for your home. For reliable air conditioning services throughout The Greater San Francisco Bay Area, call (415) 942-9188, contact us, or book your appointment today.

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