7 Reasons Your AC Runs All the Time

Becca Stokes
Written by Becca Stokes
Updated August 11, 2015
A young woman adjusting the temperature of the house by using a thermostat
Photo: Monkey Business / Adobe Stock


  • If your AC is running constantly, it’s a sign it’s time to troubleshoot 

  • The AC can’t work properly with a dirty filters, frozen coils, or closed vents 

  • Some AC issues that prohibit cooling can be handled at home, while others require a pro

  • Shorten the run cycle by keeping doors and windows closed and avoid big swings in temperature 

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Nothing takes the edge off a hot summer day like the hum of your AC kicking in. But when it never stops, that sweet sound can become a concern. Sometimes a constantly cycling air conditioner can be a sign that the unit isn’t working as efficiently as it could be. Let’s break down how air conditioners work, so you can understand what’s causing your AC to run constantly and how to fix it. 

How Do Air Conditioners Actually Work? 

Air conditioners rely on a gas called a refrigerant. Turning on your air conditioner activates the refrigerant responsible for cooling your home. 

In addition to the refrigerant, there are three other components that make your air conditioner operate: the external compressor, external coil, and internal evaporator coil. When you turn your AC on, the external compressor pulls the heat out of the refrigerant. Once the refrigerant is appropriately chilly, it is pulled over the evaporator coil. All the warm air in your home is pulled over that coil and chilled, and any water pulled from the cold air is sent out of the home through the AC discharge tube. 

Common Problems That Cause Air Conditioners to Run Constantly

A man relaxing in the sofa while listening to music
Photo: cherryandbees / Adobe Stock

There are a few different factors that can cause this common air conditioner problem

1. Air Conditioner Size

If your air conditioner isn’t cooling your home, it’s running constantly, and you can feel cool air coming out of it, you may have a too-small AC. Consult a local HVAC company to help you find the right size AC for your family based on your home’s square footage and insulation type. 

2. Closed Vents

Your air condition might be running constantly if too many vents are closed. While it’s intuitive to close your air conditioner vents in rooms that aren’t in use, too many closed vents can leave all that cold air with nowhere to go Thankfully, it’s a quick (and free) fix: simply check each room, and make sure the vents are open. 

3. Blocked Return Vents

The return vent is the grill in your home through which the hot air is sucked in to be cooled. If the unit can’t pull enough air in, it’s likely to run constantly while trying to do so. If your air conditioner is cycling constantly, check that your return vent isn’t being obstructed by boxes, furniture, or dust and debris. 

4. Dirty Filter 

If your air conditioner is running all the time, check your HVAC filter. Depending on the type of filter you have, these should be changed every one to 12 months. If your filter is dirty, it blocks the flow of air which leads to your system constantly working to try and produce the required flow of cool air. The fix? Swap out your dirty filter for a fresh one and let the air flow.

5. Dirty Evaporator and Condenser Coils

If you notice warm air coming from your air conditioner or a funky mold-like aroma in your home, it’s time to peep the condenser coils. Your condenser coils are located outside of your home, so it makes sense that they can easily become dirty thanks to landscaping debris and the changing weather (falling leaves, anyone?). 

If they get clogged, heat becomes trapped and the machine will constantly run. If you suspect your condenser coils are dirty, go take a look outside. You can usually tell with a quick visual assessment. 

If dirt is coating your evaporator coils—which are responsible for cooling your home’s air—they can’t do their job as effectively. They will need to be cleaned before your air conditioner is back in shipshape. 

If you suspect an issuer with your evaporator or condenser coils, you should call an HVAC professional in your area for an evaluation. According to HomeAdvisor, it costs between $100 and $400 to have your AC coils cleaned. 

6. Frozen Coils 

There are a few factors that can lead to frozen air conditioner coils and prevent the machine from producing cool air. These include a dirty air filter (mentioned above); broken fans that keep air from moving; and clogged condensation tubes (that take the moisture out of your home).

If you suspect frozen coils are to blame for your air conditioner running constantly, take the following steps: turn off the unit, melt the ice on your air conditioner, and contact an HVAC professional. 

7. Refrigerant Leak

If your AC is making an odd hissing-like sound in addition to not cooling your home, you might have low refrigerant levels. If you suspect a refrigerant leak, contact a local HVAC technician who can diagnose the issue and perform any necessary repairs. Once your home is cool again, you can get back to your oasis from the heat. 

How Can I Shorten My Air Conditioner’s Run Cycle?

While your air conditioner needs time to operate, it shouldn’t be running constantly. Here are some tips to follow to help keep your air conditioner’s cycles as short as possible:

  • Keep doors and windows closed. Otherwise, you’re adding to the air your AC needs to cool. 

  • Keep your blinds and drapes closed. Direct midday sun beaming into your home will raise the temperature of the air inside. 

  • Reduce how often you use the stove and oven. Consider this permission to order takeout.

  • Set your thermostat at 75 degrees instead of a lower temp. This will keep you cool without taxing your HVAC system.

  • Take control of the settings by avoiding the “auto” option. Use the “on” and “off” settings instead. 

  • Adjust your fan settings. Running fans in your home helps lower temperatures so your AC doesn’t have to work as hard to cool things down. 

  • Avoid big swings. It takes an air conditioner up to three hours to lower a medium-sized home’s temperature from 80 to 72 degrees Fahrenheit, and even longer if it’s larger.

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