Few things are as satisfying as a cool air-conditioned breeze on a hot summer day.
One thing that’s worse is an air conditioner that never stops running.
An AC that runs constantly will experience more wear and tear from its round-the-clock operation. It will also drive up your electricity bill.
In this article, I’ll go over the top causes of an AC that runs constantly. I’ll also go over how to fix an AC that runs constantly, and how to know if your AC is undersized for your home.
Causes of an AC that runs constantly
A dirty air filter, dirty condenser coil, or blocked air vents are the top causes of an AC that runs constantly.
An AC that runs constantly is usually due to an inhibition in the cooling capacity of the AC.
For example, a restriction in airflow will reduce the cooling capacity of your AC and cause it to run constantly.
Here are the top causes of an AC that runs constantly:
- The air filter is dirty
- The condenser coil is dirty
- Air vents are blocked
- Air is leaking from ducts or air handler
- Refrigerant is leaking or restricted
- AC is undersized for your home
I’ll go over these causes below.
The air filter is dirty
The top cause of an AC that runs constantly is a dirty air filter.
Why does a dirty air filter cause your AC to run constantly?
It’s all due to airflow.
If your AC’s air filter is dirty, then airflow through your system will be restricted. The airflow restriction makes it harder for your AC to cool your home.
The reduced airflow leads to your AC running constantly as it tries to keep your home cool.
If your AC’s air filter is dirty, you need to swap it out for a new, clean filter.
I recommend replacing your AC’s air filter every 1-2 months.
The condenser coil is dirty
If your AC’s condenser coil is dirty, your AC will run constantly since it will have a hard time removing heat from your home.
The condenser coil’s job is to reject heat from your home. If the condenser coil gets dirty, then it will have a hard time moving heat from your home to the outside.
A dirty condenser coil will lead to your AC working overtime as works harder to remove heat from your home.
Keep your AC condenser coil clean by spraying it down with water from your garden hose.
Don’t use a pressure washer or a high-pressure sprayer—it will damage the fins on your condenser coil.
If your AC’s condenser coil is excessively dirty I recommend using a coil cleaning spray to dislodge dirt and debris from the interior of the coil.
Air vents are blocked
If any of your air vents are blocked, your AC will run constantly as it tries to cool your home.
Some folks think that blocking off air vents in unused areas of their home makes it easier for their AC to keep their home cool.
In actuality, blocking off your air vents does more harm than good.
By blocking off air vents, the parts in your AC system will experience more wear and tear since you are effectively choking off its airflow.
Your AC also runs the risk of freezing up when you block off its air vents.
Blocking off your AC’s air vents also reduces its cooling capacity.
Basically, you’re not doing yourself any favors by blocking your air vents.
Keep all of your air vents open and unobstructed. And keep all furniture and objects at least 1 foot away from all air supply and return vents.
Air is leaking from ducts or air handler
If there are any air leaks in your AC system, your AC may run constantly.
As air leaks out of your AC system, your AC loses cooling capacity.
This means that your AC will have a harder time cooling your home and may run constantly if your AC system has air leaks.
Take a look around your AC’s air handler for any obvious signs of air leaks—such as holes, cracks, or gaps in the ductwork.
If you find any small air leaks, use some aluminum foil tape to patch the holes and keep the air flowing through your AC system.
For larger air leaks or gaps, you may need to use mastic to patch the hole.
Check out my article here for guides on how to use aluminum tape and mastic:
Refrigerant is leaking or restricted
If your AC unit has a refrigerant leak or refrigerant restriction, your AC will run constantly since its cooling capacity is reduced.
If your AC has a refrigerant leak or restriction, the first thing you’ll usually notice is that your AC is blowing warm air.
Your AC will stay running constantly as it tries to cool your home with no success.
Eventually, your AC will shut down when its refrigerant pressures get out of whack.
If you suspect that your AC’s refrigerant is leaking or restricted, you need to get an HVAC professional to run a diagnosis on your unit.
AC is undersized for your home
If your AC unit is undersized, it will run constantly as it tries to keep your home cool.
Simply put, some ACs are just not big enough to do the job.
If your AC is undersized, it will likely be an ongoing problem, especially during the hottest days of the year.
Keep in mind that most cooling load calculations don’t take into account massive deviations in yearly temperatures.
This means that if a record-setting heat wave comes into your area, your AC might not be able to keep your home cool—and that’s by design.
Let me put it this way—if your AC was sized to cool your home during a massive heat wave, then it would be oversized for every other day of the year. And an oversized AC is just as bad as an undersized one.
That being said, if your AC is running properly but still can’t keep your home cool on a normal summer day, then it might be undersized.
Get in touch with an HVAC professional to do a load calculation if you suspect that your AC is undersized for your home.