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    Why Does My AC Unit Keep Running?

    Repairman working on AC unit

    One of the most common problems that homeowners face with central AC is a unit that runs constantly. An AC unit with this problem may cycle on and off over and over again, or it may simply stay on for hours on end. This can cause massive power bills as well as unnecessary wear and tear on your AC unit. 

    You might be suprised to know that there are many different reasons that an AC unit may run non-stop. This article lists 10 of the most common issues that can cause an AC unit to keep running around the clock.

    Ten Reasons an AC Unit Runs Non-Stop


     Some of these issues can be easily fixed by the homeowner, some require a bit of mechanical skill, and others should only be addressed by a licensed professional.  To learn more about the problems that could cause a central AC unit to run constantly, read on, we'll cover ten of the most common reasons.

    Brand new Central AC Coils

    AC Coils Need to be Cleaned

    This is arguably the most common reason that an AC unit may keep running. AC units need regular maintenance, even if they are working perfectly. 

    One of the most important components of a regular maintenance service is an AC coil cleaning. Without regular cleaning, grime and dust will build up on the coils until they no longer function at optimal efficiency.

    When this happens, the coils must be cleaned immediately to restore efficient operation. A homeowner with a bit of mechanical know-how can use standard tools to open up the AC unit and wipe off the coils. However, it may be easier to simply call in a professional.

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    New AC filters at Home Depot

    The Filter Needs to be Changed

    This is another extremely common issue that can cause an AC unit to keep running. AC units have filters that must be swapped out at set intervals. How long a filter is good for depends on the specific filter, the AC unit and how heavily it is used. Filter replacement is an important part of AC unit maintenance.

    If a unit has not been regularly serviced, its much more likely that it has an old, clogged filter. Thankfully, the fix for this problem is very easy. All you have to do is pop out the old filter and put in a new one. This process is very easy, and doesn't require complicated tools or extensive mechanical knowledge.

    Setting thermostat

    Temperature Setting is Too Low

    This is yet another very common reason that an AC unit will run and run. The unit may actually be working fine, but the problem could simply be that the temperature setting is too low, and the AC unit may simply not be powerful enough to get the temperature down to your preferred setting.

    This issue is most commonly seen in hot climates with homeowners who like to keep their dwellings a little on the chilly side. The only way to address this problem is to get a more powerful AC unit installed.

    Frozen made from ice cubes

    The Coils are Frozen

    If your AC unit constantly runs, there's a good chance that the coils may be frozen. This is especially common if you've set the desired temperature to a very low setting. 

    However, even if you haven't set the temperature very low, the coils may still be frozen. It's not uncommon to see this problem with older AC units.

    The coils installed in newer AC units are designed to freeze much less often than AC units of years past. If your old AC unit constantly runs, you may want to consider getting it replaced.

    Otherwise, all you have to do is shut off your AC unit for as long as it takes for the ice to melt. The amount of time it takes varies depending on the temperature, and the amount of ice built up on your AC unit's coils.

    Road sign with right and wrong

    Incorrect Filter Type Installed

    In recent years, this problem has become more common. Over the last few years, filters that remove particulates like pollen and dust from the air have become more common and more popular among homeowners. 

    Although, these filters help people with allergies avoid reactions to the air in their home, there is a hidden drawback with these filters. AC filters that are designed to remove an especially high percentage of particulates often don't allow enough airflow. Which could be the culprit if your AC unit is constantly running.

    Check your AC unit's manual to see if you have the right kind of filter installed. If you don't, you can easily put in the right one yourself. Depending on the type of AC unit you have, you may not even need tools! Most units make it easy to take out the old filter and insert a new one by hand.

    AC Coils

    The Coils are Leaking Refrigerant

    Although this is a less common reason, it's also potentially more serious. Refrigerant needs to be constantly pumped through the coils of your AC unit so that they are cold enough to do their job.

    The greater the workload on your unit, the more refrigerant must be pumped through the coils. Old units and AC units that are used very heavily are prone to developing refrigerant leaks.

    Even new units that have defective coils can develop leaks. If you open up your unit and notice that liquid is leaking off of the coils, call a professional immediately. There's a good chance that the coils need to be replaced. This is a fairly complicated job that's best left to licensed professionals.

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    Old style thermostat

    Faulty Thermostat

    There's a chance that the problem isn't the AC unit's fault at all. Sometimes the culprit is actually the thermostat. If the thermostat is faulty, it could be telling the AC unit to maintain a colder temperature than the one you set.

    To test this, set the thermostat at a relatively high temperature and get a thermometer. If the thermometer reads several degrees below the setting on the thermostat, you've found the problem.

    The thermostat will need to be replaced by a professional unless you have considerable mechanical skill, and feel comfortable taking on the job yourself.

    Repairman cleaning home ductwork

    Leaking Ducts

    This is another issue that doesn't actually originate with the AC unit itself. If your AC unit is constantly running in a vain attempt to maintain a cool temperature, the problem could be the result of leaky ducts.

    Cool air may be leaking from your ducts before it reaches the register. Although, it's possible to check this issue yourself, it can be a little tricky as you'll likely need to crawl around your attic looking for holes within the air ducts.

    For those living in an apartment or condo without an attic, contacting a professional to do the inspection is a must. However, if you do look yourself, take an especially close look at the areas where two ducts meet or the ducts enter the walls. These are the most common sites of air duct leaks.

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    Outside HVAC unit

    Dirty/Clogged Condenser Coil

    There's one fairly common issue that occurs within the condenser unit. Since the condenser unit is commonly located outside near the house, it's exposed to the elements. It's not unheard of for condenser coils to clog. 

    When a condenser unit does get clogged up, the most common culprit is a buildup of sticks and leaves. However, keep in mind that it could be a dead animal or something else.

    Whatever it may be, it's fairly easy for the homeowner to unclog their condenser unit themselves without having to call a repairman. Just be on the look out for any damage to the condenser's mechanical parts that may have occured. If there is damage, you're best choice is to call a professional to do the repairs.  

    Fan on top of HVAC unit

    Malfunctioning Fan

    A malfunctioning fan could also cause your AC unit to constantly run. Or, it could simply be that the fan is on too low of a setting to achieve your desired temperature.

    Before assuming that the fan isn't functioning as it should, first check that the fan setting isn't too low. If the fan's setting is fine, next check and see if the fan's blades are dirty and grimy.

    Dirty and grimy fan blades can impede optimal operation. But, don't worry, it's an easy fix. All you need to do is wipe off the fan blades in much the same way you would clean the AC coils.

    If after cleaning your blades the fan is still not functioning properly, there may be an electrical problem. At this point, you should call a professional. 

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