Why does my air conditioner keep turning off?


If you have noticed that your air condtioner comes on and runs for ten to fifteen minutes then shuts off and ten to fifteen minutes later starts up - you may be wondering what is wrong with it. If you air conditioning system starts and stops frequently, this is called short cycling

What is short cycling?

Short cycling of an ac system occurrs when the system shuts off and then starts again in a rapid fashion. There are a variety of reasons why your air conditioner may be short cycling - unfortunately none of them are good news for the efficiency or effectiveness of your ac unit. In many cases it means that the space your attempting to air condition will not achieve its set temperature.

Why is short cycling bad for your air conditioner?

The simplest analogy of why your air conditioner shutting off repeatedly is bad for it is likening it to a car. Lets say you were going on a 1 hr journey in your car - and that every 10 minutes you stopped the car, waited for 10 minutes and then started driving again. Not only would you take twice as long to get there you would also:

  • use more fuel, as you are repeatedly accelerating and decelerating;
  • create more wear and tear on your car due to the repeated starting and stopping of your engine.

The same is true of ac unit, short cycling will mean:

  • it takes longer for your room to get to set temperarture
  • you will use more energy to get to the set temperature
  • you will have greater wear and tear on your air conditioner

When you have a short cycling air conditioner it can also mean there is an underlying problem with the ac system.

Common causes of short cycling

  1. Dirty Air Filter

    A dirty air filter will mean that there is insufficient air flow to the evaporator coils. The air conditioner works by blowing air over the evaporator coils when then heats \ coils the air as necessary. When there is insufficient heat transfer over the evaporator coil the operating pressure in the air conditioner can move outside its normal operating range, causing the air conditioner to turn off.

    Not only can dirty filters cause an air conditioner to turn off - they will also lead to increased running costs for the ac system. The best way to address this is through regular servicing of your air conditioner.
Dirty Air Filter
  1. Blocked Coils

    In the same way a dirty air filter impedes air flow, likewise dirty evaporator coils or dirty condenser coils can also impede air flow. This will also mean the ac system will stop running to operating pressures being outside of their normal range.

    Dirty \ blocked coils will also lead to higher energy bills as air conditioning units with blocked coils do not have effective heat transfer and hence need to work harder to achieve the same outcome as they would with clean coils.

    The best way to keep coils clean on air conditioning systems is through regular maintenance. Cleaning the out door coil on a system is normally relatively. Cleaning the indoor (evaporator coils) can be easy on a wall mount system, but much harder and more expensive when you have ducted air conditioning. The best way to prevent his becoming an issue is cleaning your air filters before they become too dirty.
Blocked Coils
  1. Low refrigerant

    Low refrigerant in an air conditioning unit can be a cause of frozen evaporator coils. When you have frozen evaporator coils this wil in turn impact the operating pressure of the system causing the system to shut off.
  2. Faulty controller

    If your air conditioner controller is faulty it may cause the system to short cycle. The most likely culprit will be the thermostat within the controller. If it is still working, but no giving a true reading, it could cause the air conditioner turn off even though the room is not at the desired temperature.
  3. Thermostat in a poor location

    Another reason for air conditioner to turn off, even though the room is not set temperature is because of a poor themostat location. If the location of the thermostat has poor air flow, or is not representative of the temperature of the room - for example it has cool air from the air condtioner blowing directly on it, from a supply vent, this could cause the system to turn off prematurely.
  4. Air conditioner is oversized

    Air conditioner have a set operating range, determined by their capacity. If the capacity of your air is signiciantly more than the space your are trying to cool then it will cool the space very quickly then shut down. The space will then heat up, causing your ac system to start again and then quickly shut down. This process is extremely inefficient and causes excessive wear and tear on your air conditioner.This a problem caused due to incorrect sizing of the system during the design process prior to installation of the air conditioner - this is particularly a problem when choosing the size of a wall mount split system to install.

What to do if your air conditioner is short cycling?

Almost all causes of an ac short cycling can be diagnosed and rectified. The best way to get this done is by calling an experienced and licencsed air conditioning maintenace provider like Sun City Air Conditioning

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