Air Conditioner Keeps Running After Reaching Temperature Setting
What does it mean when an air conditioner keeps running after reaching temperature setting on the thermostat when it's supposed to shut off until the next cycle?
Are you aware this could indicate there is a problem and do you know how to solve it if it is?
Let's look at the issue:
When the room temperature reaches that set by the thermostat, but the air conditioning fails to automatically shut itself off as you would expect it to do, you may also notice one or more related issues becoming apparent.
These could include:
- Continuous noise
- Increased electricity bills
- Excessive cooling
- Fans and vents icing up
- Water dripping from vents
If any of these issues is noticed, it may be an indicator that there could be a component failure or even internal damage to the equipment that would need repair.
Now let's take a look at some probable solutions to the problem.
How Long Should Air Conditioning Run to Cool a House?
First of all, we should ascertain how long an air conditioner should be working in order to cool the entire house to the set temperature.
In general, a typical air conditioner will cycle off an on every 15 to 20 minutes as it cools the entire house, eventually shutting off once the set temperature has been reached.
It will restart after some time when the temperature starts to climb above the set temperature, depending on how long it takes for the temperature to rise.
Certain conditions will dictate the on-off cycle period and the time it will take to restart after shutting off when working normally. Let's take a look at these:
Air Conditioner Size and Power Output
The size and power output rating of an air conditioner should be relevant to the internal volume of the building it is installed in to cool.
If the air conditioner is too large or too powerful compared with the size of the house, it might be possible to cool the entire area in a much shorter cycle time, say 10 minutes or so. However, that may not be desirable.
A too large or too powerful cooler will generally equate to greater energy consumption, which is unnecessary and costly. It may also dry the air excessively, leading to potential respiratory problems especially for occupants with existing respiratory conditions.
On the flip side, a too small or underpowered cooler with struggle to reach the set temperature by overworking and again drawing far more energy than necessary.
An undersized AC may not reduce the humidity in the air as effectively, with a tendency to make the house feel more humid. An overworked AC may also lead to higher risk of components breaking down with associated repair costs to worry about.
Outdoor Temperature
The temperature outside will have an affect on the cooling power of an air conditioner.
To give you an idea of how this can affect the running of an AC, when it's too hot or humid in your area, the cycle can be longer than 15 to 20 minutes to cool the entire house. Likewise, when the outside temperature is moderate, the cycle can be faster.
With this knowledge, it is possible to determine how long it can take an AC to cool your house.
How Long Should an Air Conditioner Run Each Day?
It is also useful to know how long an AC should be allowed to run each day. Again, this will depend on a number of mitigating factors, such as:
Air Conditioner State and Efficiency
One important factor that has an effect on the ability of the equipment to cool your home is the overall state it is in and its efficiency.
A well-maintained standard or self evaporating air conditioner that is in good condition will tend to run more efficiently and thereby be more effective at cooling your space while also being more economical to achieve and maintain a comfortable indoor temperature.
Aside from the equipment's condition, there are external factors that affect the run times and effectiveness of air conditioning. These include:
Outdoor Temperature
It is fairly obvious, when you sit down and think about it, but the outdoor temperature will have an effect on how long an AC will need to run for to cool the whole house.
On those very hot summer days, the AC will need to keep running throughout the day. If the nights are also hot and especially when they're also humid, the AC will need to run throughout he night, albeit perhaps on a slightly warmer setting to conserve energy and not make the house too cold to make sleeping uncomfortable.
There is a method of reasoning that supposes that frequently turning the AC off and on throughout he day will help to conserve energy.
Energy Usage
However, studies have shown that this practice actually increases energy usage while also leading to "short cycling," which can affect the performance of air conditioning equipment and also lead to greater instance of wear and tear, reducing the lifespan of the equipment.
When the outdoor temperature is milder, it might be possible to run the AC for short 10 to 15 minute cycles to maintain a cool indoor climate. However, to obtain the best economy from an air conditioning system, it is better to rely on the thermostat.
The thermostat's job is to regulate the temperature and automate the running cycles to match the external climate factors, than to try and do so by manually turning the AC off and on. That leads us on to the next factor:
Thermostat Setting
How the thermostat is set has a major effect on the AC running duration as well as its efficiency and economy with regard to energy usage.
If the thermostat's temperature setting is especially low, you will need to keep the AC running for longer periods, especially during very hot weather.
By sensibly adjusting the thermostat's temperature setting to a level that is not too cold but rather more comfortable as it should be, it is possible to reduce the AC run cycle time. This will also reduce its consumption of energy, helping to save money on electricity bills.
Air Conditioner Size and Power Rating
The size and power rating of a regular or even smart air conditioner is a major factor in how long it will run for.
If it is too large and over-powered for the size of the space to be cooled, it will certainly cool the space in a shorter time, but will use far more energy than is necessary to achieve that level of indoor temperature and climate comfort.
If, on the other hand, the AC is too small or under-powered for the size of the space to be cooled, it may need to run in longer cycles (approx 20 minutes cycle) to cool the space. It will also cause greater load on the cooling equipment leading to a shorter life span.
It is therefore very important to size the cooling equipment correctly for the space it is intended to cool. A correctly sized AC can be more efficient and economical while lasting longer due to reduced load and wear.
Size of the Space
Lastly, the dimensions of the habitable inside area of your house is a deciding factor on the cooling effectiveness of an air conditioner.
If the space is particularly large, depending on the size and power output of the equipment, the AC may need to run for a longer duration to maintain a cool indoor temperature.
If you own a small, portable air conditioner that may not be up to the task, it would be sensible in order to reduce energy wastage to use it cool only the room (or rooms) which you are using. Maintain unoccupied rooms with the doors and windows closed to reduce the possibility of the heat from those rooms leaking into occupied rooms that are being cooled.
For smaller spaces, it is necessary to keep a smaller portable AC running for long enough to maintain a comfortable temperature.
How Long to Cool a House From 80°F to 72°F?
If you need to cool your house from 80° to 72° Fahrenheit, first consider some of the above points mentioned.
In general, it would take a well sized and balanced AC around 4 to 6 hours to cool a moderately sized house from 80° to 72° Fahrenheit on a moderately warm day. That is as long as it is running as efficiently as it can and the vents are not blocked.
10 Reasons an Air Conditioner Keeps Running After Reaching Temperature Setting
If the AC has reached its set temperature but keeps running afterwards, there should be a reason for it. Knowing what it is may help to prevent unnecessary wear of AC components and excessive electricity consumption.
Below are 10 common reasons why an air conditioner keeps running after reaching its thermostat setting:
Evaporator Coil Is Dirty
A dirty evaporator coil can be a major reason for causing an air conditioner to continue running after reaching its temperature.
The purpose of the evaporator coil is to cool the refrigerant gas so that it can absorb heat from the air. Often, humid air can contains dirt, dust and debris, which accumulates on the evaporator coil. This can cause it to function more slowly than normal, causing the air conditioning system to run slower.Solution:
The solution is to clean the evaporator coil. Either call a professional HVAC engineer to clean the coil or you can do it yourself if you have good handyman skills.
Here are some steps you could take to clean the evaporator coil:- Add mild detergent and warm water in a spray bottle and mix them
- Spray the evaporator coils with this solution
- Allow the solution sit there to soak up the dirt and debris for a few minutes
- Wipe away the dirt-laden solution using a soft cloth
If the coil is heavily soiled, it might be better to call a professional to clean it.
Evaporator Coil Is Frozen
If the evaporator coil has frozen, a clear sign is feeling warm air emitting from the air conditioner, as it continues running.
Solution:
A little investigation is necessary to ascertain why the evaporator coil has frozen. This can sometimes be a job for a professional, but you can follow these steps to unfreeze the evaporator coil:
- Turn off the air conditioning and allow the frozen evaporator coil to thaw for 24 hours
- While it is thawing, clean the evaporator coil if it appears dirty
- Check the air filters are clean. Replace them if they are soiled
- Check for any damage to the evaporator coil. If it appears damaged, call a technician
In many cases of frozen evaporator coils, it is best to call a technician who can also check the refrigerant levels are correct and check for leaks, repairing or replacing any component that requires it.
Air Filter Clogged
Clogged up air filters can cause all kinds of problems. When the air filters are clogged with dirt or debris, the air flow is reduced through the system.
In this case, it can take longer to cool the house correctly, leading to the AC continuously running.Solution:
Purchase replacement air filters, remove the old ones and fir the new ones (making sure the filters are facing the right way – see instructions).
Many AC systems have reusable air filters that you can easily remove, vacuum out debris and then wash with a mild soap solution before replacing them.
It is a good idea to make a point of cleaning or changing the AC air filters regularly.Excessively Restrictive Air Filter
Air filters with a high MERV rating can be quite restrictive of air flow. This can be a cause of an air conditioner running longer since it requires more time to cool the space.
Solution:
If you determine this is a problem, replace the air filter with one that has a lower MERV rating, typically between 8-11 for home or light commercial use.
Leaks in Ductwork
This is a common problem in older buildings where there is old ducting.
Cool air may be escaping through any leaks in the ducts, making the air conditioner work harder and run continuously in order to keep the house cool.Solution:
Leaking ducts can be tricky to fix, since a lot of time and effort can go into detecting and repairing the leaks or replacing very old ductwork.
Doing the work yourself can be cheaper than calling a professional, although lack of experience can in turn become expensive, making it better in many cases to call a professional and alloow them to diagnose and fix the problem.Thermostat Issues
Occasionally there can be thermostat problems that may cause the air conditioner to keep running despite reaching the set temperature.
If there is a problem with the thermostat, it may not sense it is at the set temperature and fail to turn off the system.Solution:
Check whether there is an actual problem with the thermostat. Often this will require the services of a technician. If there is a problem, it is usually best to replace the thermostat with a new one.
Low Refrigerant
When the refrigerant level is low, the AC may keep running to maintain a cooler temperature.
This often occurs when there are leaks present in the system, typically the evaporator coil. This can cause the AC to work harder to keep the place cool, along with other issues.Solution:
This is a situation where you'll need an HVAC professional to locate any leaks and repair them.
It could be possible to use a freon leak repair kit for small leaks yourself, but the best advice is to call a professional.Condenser is Dirty
A dirty condenser can make air conditioning continue to run after reaching the set temperature, in a similar way to a dirty evaporator coil.
The accumulation of dust, dirt, leaves and other debris can impede the airflow. This can make the cooling system function improperly.Solution:
You could clean the condenser unit or coil yourself by using a good quality condenser coil cleaner. Here are some handy steps you can follow:
- Inspect the condenser coil and its housing for fallen leaves or other debris
- Use a coil brush to clean the debris from the condenser unit
- Be sure you straighten out the coil fins after brushing
- Use a foaming condenser coil cleaner to further clean the area
- Leave for 10 minutes and then wash away the foaming cleaner
Incorrectly Sized Air Conditioning Equipment
This is applicable if you have changed the cooling system or equipment, or altered the layout of your home.
The problem may be that the AC might not be the correct size or power output enough for the building or its layout.Solution:
This problem is usually best solved by calling a professional to perform a load calculation. This can help by providing you with the best solution depending on your circumstances.
Blower Motor or Fan Issues
An air conditioner may continue running after reaching its set temperature if there an issue with the fan or blower motor has arisen.
It could happen that the blower motor may not be providing the correct volume of air, or the fan may be working too slowly.Solution:
If possible, adjust the fan speed accordingly. In cases where the fan blades are dirty or caked with debris, clean them and you may see effective results. If the fan or blower motor are old and failing, you may need to get an HVAC technician to replace them.
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Final Thoughts
Make it your mission to discover the issue with the air conditioner by going through the above points and checking to see if one or more of them is a likely cause. You can then undertake respective solutions either by doing the work yourself or calling a professional to do it for you.
It is important to keep your air conditioner in a good condition and running efficiently to prevent excessive run-on after the set temperature is reached. This is to avoid excessive energy consumption and associated higher electricity bills to cut the cost of air conditioning as well as preventing and potential damage that might occur.
Last Updated: September 9, 2022
