Is your central air conditioner is running constantly? This leads to a big energy bill and can even damage your cooling system! Below, the heating-and-cooling experts at Home Service Plus® (HSP) share the most common reasons why a central AC unit may run continuously. Starting with the easiest-to-fix problems, let's explore why your air conditioning doesn't stop running.

Troubleshoot a central air conditioner that runs continuously

Don't skip past easy-to-fix reasons why your air conditioner is running continuously. If you're lucky, your air conditioning is constantly running because of a simple matter – not broken AC equipment!

Simple reasons why your AC may run constantly:

  • Windows open or external doors left ajar (check your children's rooms!)
  • Thermostat settings (more on that below)
  • HVAC blowerfan is constantly running – not your AC unit

Is There Truly a Problem? 

The higher the temperature, the harder your AC is going to have to work to keep you cool. Even a seemingly small increase in the outside air temperature can cause your central air conditioner to run longer. In other words, expect your AC to run longer cycles when it's 90 degrees outside, compared to a temperature of 85.

#1 Filter issues

Dirty, clogged or overly restrictive filters may be the cause of many heating-and-cooling problems, including a constantly running AC system.

What you can do:

  1. Turn your air conditioner off.
  2. Remove and inspect your HVAC filter. Does your filter appear dirty? It may be jammed up with so many particles that it's restricting your AC air flow!
  3. Ensure your filter isn't too restrictive and meets manufacturer recommendations.
  4. Clean/replace dirty or clogged filters as necessary.  
  5. Install or reinstall new filter (ensure you install it to face the correct direction).
  6. Turn your AC back on.

Home Service Plus customers in Minnesota can get special discounts and FREE shipping on the largest online selection of name-brand filters through our partnership with the Discount Filter Store.

#2 Air flow problem

If a home's air flow is compromised, it may make the air conditioner run constantly.

Troubleshoot AC air flow problems by checking for:

  • Closed/blocked vents
  • Leaky air ducts and other ductwork problems
  • Worn out blower motor

Your HVAC system was designed to deliver cool air throughout your entire ductwork. Your AC may actually work harder if you restrict/block where the air can flow. Do not try to save money on cooling bills by blocking vents in rarely-used areas of your home, unless you have consulted a heating ventilation and air conditioning (HVAC) contractor who says it's okay to do it!

What you can do:

  1. Check your vents and air returns to ensure they aren't obstructed by furniture, drapes, etc.
  2. If you have dampers, make sure they are fully open.
  3. You may also inspect your ductwork while air is flowing through. Can you feel any air leaks? Air duct leaks are more likely to occur at joints (where separate pieces of ductwork meet).

An HVAC contractor has tools to digitally measure pressure and help diagnose air flow problems. From a bad blower motor to leaky ductwork, an expert can help diagnose and fix causes of weak AC air flow.

Note: If you live in the Minneapolis/St. Paul metro area, or greater Minnesota (see Cities We Serve), you can contact HSP 24/7 to arrange an AC tune-up or repair service. We've been helping MN homeowners with cooling and heating for 80+ years.

#3 Thermostat needs to be replaced

A bad thermostat can cause a variety of heating and cooling problems. Is your AC running continuously and your indoor air temperature cooler than what the thermostat is set to? That may indicate a faulty thermostat.

What you can do:

  • Check your thermostats settings, including its set point (the desired temperature you set).
  • If it's a programmable thermostat, ensure you haven't accidentally programmed set points that are too low (too cool).
  • If your digital thermostat has a reset option, give it a try and see if it helps.
  • You can also explore our pro tips for using your thermostat.

A heating-and-cooling expert will help diagnose the reason why your air conditioner won't turn off. If the thermostat is the cause, an AC repair service should be able to replace your failing thermostat.

#4 Evaporator coil is dirty or froze up

A dirty evaporator coil will weaken your central AC's ability to effectively cool your home. The decrease in efficiency will make it work harder and run longer to achieve your desired indoor temperature.

What you can do:

  • Contact your Home Service Plus experts to schedule service – most modern AC units have tightly sealed evaporator coils and require professional servicing (coil cleaning is part of a quality central AC tune-up).

A frozen evaporator coil can also make your AC unit run constantly, potentially causing equipment damage and exposing your home to water damage. Reduced air flow is one possible cause of a frozen evaporator coil.

What you can do:

  1. Turn off your AC via the thermostat and put it in "fan only" mode.
  2. Follow the steps mentioned in Filter Issues (above).
  3. Follow the steps in Air Flow Problem (above).
  4. Get absorbent towels ready (in case ice thaws in your unit and creates excess water).
  5. Call our HSP HVAC expert to inspect your AC unit to help avoid a repeat of the issue.

Available 24/7/365, you can contact HSP's customer service representatives to schedule AC repair service.

Diagram of how a home central AC system works, transferring heat from inside to outside the house, lowering inside temperatures.

Source: U.S. Department of Energy

#5 Refrigerant is low or leaking

Refrigerant is an important part of your air conditioner. If your AC refrigerant is undercharged or overcharged, it will decrease its ability to cool your home (and shut off). An AC technician will be able to check the refrigerant level with special gauges to see if it's low (undercharged) or too full (overcharged).

What you can do:

  1. Look for ice accumulating on the lines between your home and outdoor AC unit.
  2. Look for puddles or pooling water (from melting ice) near the outdoor AC unit.
  3. Call your HSP repair technician if you believe your AC may be leaking refrigerant.

If your outdoor AC unit is leaking refrigerant, call an AC repair service immediately! Do NOT try to keep your leaky AC unit operating by regularly refilling its refrigerant.

Note: Refrigerant is sometimes still referred to as Freon, a brand name for R-22. Freon is an environmentally hazardous substance being phased out by the U.S. Environmental Protection Agency (EPA). Learn more by reading FAQs about Home Air Conditioners that Could Contain Freon at the EPA's website.  

#6 Improperly-sized AC unit

Is your AC system relatively new? If it seems to be running much more often than your old system, it may (or may not) be because your central air conditioner is undersized. Or, your AC seems to be running continuously because your previous unit was oversized.

Sometimes a central air conditioning unit in your home will be slightly oversized or undersized by design (on purpose). If you had the choice between a slightly oversized or undersized AC, the HVAC contractor should have assessed your cooling needs, efficiency of your home, and your local climate to give you a recommendation on which of the two options is best for you. 

An undersized AC may run a bit more often than you'd like, but could still be the right choice versus an oversized central air conditioner. An oversized AC may make your home uncomfortably cold during a cooling cycle (creating wide, in-home temperature fluctuations) and inflate your energy bills, despite running shorter cycles.

What you can do:

  • Schedule our HSP central air conditioning service professionals to inspect your AC unit and ductwork.  

At HSP, we offer FREE in-home consultations to homeowners considering a new central AC system. This ensures your new equipment will be the correct size for your home and lifestyle. The free consultation also gives you the chance to review all your options and ask us questions.   

Need Repair of a Constantly-Running Central Air Conditioning Unit?

Home Service Plus has 80+ years of experience meeting Minnesota homeowners' needs for heating and cooling. You can benefit from the state's largest staff of certified, licensed and pre-screened technicians by choosing HSP.

Our AC service area includes:

  • Minneapolis
  • St. Paul
  • Twin Cities metro area
  • Much of greater Minnesota

Schedule service online or call Home Service Plus at 800-333-9365.