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Why Is My AC Short Cycling? Answers From a Phoenix Tech

July 29, 2019

Short cycling is when the unit reaches set temperature too quickly due to many reasons such as the thermostat is bad, installed wrong, cold air blowing on it, hole not sealed behind it, Oversized unit, Fan set too high a speed, or air not circulating the home properly.

If there is a problem with the unit or its a pressure switch tripping causing unit to repeatedly turn on and off its not actually considered short cycling if it never gets to temp in the house.

The following reasons can cause your AC to short cycle:

  • Your AC is too large for your home
  • Your thermostat is in the wrong location

However, there are other reasons your AC may be turning on and off frequently that don’t technically mean your AC is “short cycling,” but can cause the same discomfort in your home.

Your AC may be turning on and off frequently (but not necessarily “short cycling”) if:

  • Refrigerant levels are too low
  • Low airflow to your AC system
  • The evaporator or condenser coil is dirty

Below, we’ll walk through how each of these issues causes your AC to turn on and off and what you can do to fix it.

Need a professional’s help now? We do our best to fix your AC as quickly as possible, so if you need service…

Reason #1: AC is too large for your home

If you’ve recently installed a new AC system and it’s frequently turning on and off, this is likely your issue. When an AC system is too large for your home, it will cool your home quickly and then shut off.

When your AC short cycles, it not only turns on and off frequently but causes other issues, like:

  • Increased energy bills
  • Shortened AC lifespan
  • Increased chance of an expensive repair or replacement

The solution:Contact an HVAC professional to come to your home and perform a load or cooling calculation. This will determine how much heat needs to be removed from your home and what size AC should have been installed.

If your AC is oversized, you should consider contacting the company or contractor who installed your AC system. If it’s within warranty, this may help with the cost of replacing your oversized system.

Reason#2: Thermostat location

Your thermostat is supposed to assess the temperature of your home and signal your AC system to turn on in order to cool your home.

However, if your thermostat is located close to an AC vent or near a window, it may not be able to read the temperature of your home accurately, which means you may turn your AC on only to have it shut off in a few minutes.

The solution:Hire a professional to come and move your thermostat to a better place in your home where it can more accurately read the temperature.

Reason #3: Low refrigerant

Refrigerant is the substance that carries heat out of your home. It circulates throughout your system in a closed loop. However, if there is a leak in your refrigerant line or coils, the refrigerant will spill out of your system.

When refrigerant levels are too low, it can lower the overall pressure of your AC system, which can trigger a safety switch and turn off the compressor (the part of your AC that “pumps” refrigerant in and out of your home).

When the compressor shuts off, the pressure will rise again and your AC will start back up.

Once your AC system senses that the pressure is low (due to low refrigerant), it will shut back off again, causing this rapid on/off cycle you’re noticing.

The solution:Contact a professional to repair your refrigerant leak and refill your refrigerant.

Note: You should be wary of any tech that will refill your refrigerant without repairing the leak first. There is no way for your system to be low on refrigerant unless there is a leak in the system, so it will cost you more, in the long run, to keep refilling refrigerant than to first repair the leak.

Reason #4: Low airflow

Your air conditioner needs to bring in a steady amount of warm air to run efficiently. If something is preventing your AC from pulling in enough warm air to cool, components like the blower have to work extra hard to compensate.

If these components overheat they will turn off to protect themselves from damage. Once the parts have cooled down, they turn back on again.

What blocks airflow to your AC?

Low or blocked airflow to your indoor AC unit can be the result of:

  • A dirty air filter
  • Blocked vents
  • Leaky ducts

The solution: Replace your AC filter and ensure that your return and supply vents aren’t blocked by anything (furniture, curtains, etc.) If your AC is still turning on and off, you should call a professional. You may have leaky ductwork that a professional will need to evaluate and repair.

Reason #5: Dirty evaporator and condenser coils

As we mentioned above, your evaporator coil is where refrigerant absorbs heat from your home’s air. If your evaporator coil is dirty or blocked, it will struggle to absorb as much heat as it needs to cool your home. This added stress can cause your AC system to overheat and shut off.

Similarly, your condenser coil is where refrigerant releases the heat from your home, outside. If the condenser coil is dirty, your AC can’t get rid of the heat as easily, and this can also put a strain on your system, causing it to overheat and shut down.

The solution:Hire an HVAC technician to clean and maintain your AC system. Ideally, you should have a technician come once a year to perform a check up on your system. This way, issues like this will be prevented. Learn more about our AC check up and VIP maintenance plan.

Ready to have your AC stop short cycling? Call Phoenix's best: Patrick Riley

If you think you are experiencing any of the issues listed above, you should call a qualified technician ASAP. Using your AC when certain parts are not working correctly will not only increase your monthly energy bills but increase the chance of an expensive repair or a replacement.