4 common AC problems (and how to troubleshoot them).


By Claire Blystra

Unexpected AC problems can be annoying and even dangerous during the hot, humid summer months. Although you may be able to fix some common AC issues, others will likely require a professional’s expertise. 

Check out these AC troubleshooting tips for four common central AC problems. We’ll help you figure out what’s wrong with your AC — and when it’s time to call in a pro for backup.

Troubleshooting air conditioner problems can help you determine whether you can fix the issue from home or if you need to consult a professional. If your AC isn’t working right, you’re probably facing one of these common problems.

Problem #1: Air conditioner not blowing cold air but running.

You can hear your AC running, but the air coming out isn’t exactly cold. Sound familiar? Your AC may not be blowing out cool air for a few reasons. Check to see if:

You have a faulty or incorrectly set thermostat. Is your thermostat turned on? If so, check the temperature it’s set to. If that looks correct, check your thermostat settings to make sure the fan on your thermostat is set to “auto,” not “on.” If it’s set to “on,” your AC will push out room temperature air even when your home feels comfortable.

You need to change your air filter. Every AC is equipped with an air filter, which pulls dust and dirt from the surrounding air before the air gets drawn into the unit. This keeps your AC unit clean and maintains your home’s air quality. Air filters should be cleaned or changed every one to two months during the summer. If they get too dirty, air filters restrict the amount of air that gets treated by your AC unit.

Your refrigerant levels may be too low. If you have low refrigerant levels, your unit won’t be able to absorb as much heat from the air, so the air treated by your AC will feel room temperature instead of cold. You might be able to tell that your refrigerant is leaking if you see drainage around your unit or notice you have a frozen evaporator coil. 

Bill Fortner, co-owner of Blue Label Services in Cypress, Texas, says that there’s one very important thing to keep in mind if your AC isn’t cooling properly due to low Freon levels: don’t turn your thermostat down further. “Some think turning the thermostat down even more will make it cool better, but this is not the case … this could cause the indoor coil to freeze up.”

Refrigerant is a toxic pollutant, and it should only be handled by a professional. If you suspect a leak, contact a technician as soon as possible.

Other possible reasons your AC is running but not cooling include:

  • Your capacitor may need repairs.
  • The condensation drain is blocked.
  • Condenser or evaporator coils are dirty.
  • The evaporator coil is frozen.
  • Something is blocking the condenser unit.
  • Your AC compressor is going bad. 

Main takeaway: You can replace air filters and reset your thermostat yourself, but refrigeration leaks and capacitor problems should be handled by a professional.

Related: How much is AC service near you?

Problem #2: AC runs constantly.

“An air conditioner can run all day long and have no ill effects except aging and wear and tear,” says Fortner. However, if it runs all day long, “there is an issue with the operation, assuming it was sized correctly to begin with. It should run two to three times per hour and satisfy the setting on your thermostat.”

If your AC continuously runs, there are several possible reasons. For example:

Your thermostat might be set incorrectly. Start by checking your thermostat settings to make sure your fan is turned to “auto,” not “on.” Next, check what temperature your thermostat is set to — if it’s accidentally been set too low, your AC might be struggling to adequately cool your home, which will make it run continuously.

Your AC unit is dirty. If your air filters are clogged, change them. If your evaporator coil is dirty, clean it. The evaporator coil is where heat exchange occurs. A dirty coil might prevent your air from being cooled, which could cause your AC to run constantly and waste energy. 

Your AC might be too small for your home. An AC unit that’s too small will not be able to adequately cool your home, but it will run continuously to try. A qualified technician should have sized your AC unit during installation by factoring in your home’s layout, insulation, windows/doors and square footage, among other factors.

Main takeaway: Check your thermostat, change your air filter and clean your evaporator coil first. If your AC continues to run constantly, it might be undersized. An HVAC professional with Thumbtack can help you correctly size a new unit.

Problem #3: AC turns on and off repeatedly (or short cycling).

This problem is so common it has its own name — short cycling. Short cycling is when your AC unit turns on, cools your air a little, then shuts off. Because your home’s air was not fully cooled, your AC turns on again quickly, starting the cycle all over again.

Troubleshooting AC short cycling is simple. Follow the steps below to find out why your AC is acting up:

Step 1: Change your air filter. Dirty air filters cause all sorts of problems, including short cycling. Pull it out and see if it looks dirty. If so, replace it with a clean filter.

Step 2: Check your evaporator coils. If they’re frozen or dirty, your system may overwork and shut off. Frozen evaporator coils may also be a sign that you have refrigerant issues. 

Step 3: Call for backup. If your unit continues to short cycle at this point, you’re probably going to need professional help to diagnose and fix the issues. That’s because it might mean a few things, such as: 

  • Your refrigerant levels are low.
  • Your AC unit has broken or failing parts.
  • Your thermostat is incorrectly placed.
  • Your AC is oversized.

If you need help troubleshooting air conditioner short cycling, get an HVAC professional to take a look.

Get a free estimate from a great HVAC technician near you.

Problem #4: AC won’t turn on.

Troubleshooting AC energy problems is fairly straightforward, but fixing them may not be. 

If your AC won’t turn on, start by checking the circuit breaker. Flip the switch for your AC, and see if it resolves the problem. If the circuit trips again immediately, don’t flip the switch again. Contact an electrician for help.

If the circuit is on but your AC still isn’t working, check your thermostat. Take out the batteries and replace them — or try resetting it if you have a reset button. Additionally, make sure your thermostat isn’t set too high.

Related: 5 signs your AC is on the fritz.

Tired of troubleshooting AC issues? Hire a pro.

The best way to keep your AC working well year after year is to perform regular maintenance. Maintenance keeps your AC unit clean, which helps it run efficiently. Scheduling annual maintenance also allows HVAC professionals to identify components that require repairs or replacement.

A properly running AC keeps your family safe and comfortable throughout the summer months. If your AC isn’t working quite right, you may be able to fix it yourself using some AC troubleshooting. For more complicated problems, find an AC professional on Thumbtack. 


How do I reset my air conditioning unit?

Consult your owner’s manual for complete instructions. In most cases, you can reset your central air conditioning system by turning your thermostat to the “off” position. Then, locate your circuit breaker, and switch the circuit to your air conditioner to “off.” Wait for 30 seconds before turning the circuit back on and returning your thermostat to the “auto” position.

Where is the AC reset button?

Some AC units are equipped with a reset button. To check if yours has a reset button, consult your owner’s manual.

What causes an AC to stop working?

There are many reasons a central air conditioning unit may stop working, including broken parts, clogged air filters and low refrigerant levels. If you’re having trouble identifying why your AC stopped working, connect with an HVAC professional on Thumbtack for support.

How do you know if your AC needs Freon?

If refrigerant levels are low, you might notice your AC is running continuously, your electric bill is unexpectedly high or there’s ice or leaking on or around your AC unit. Freon is a toxic pollutant, so if you suspect it’s low, contact a professional to help.

How can you tell if your AC compressor is bad?

If your AC unit is making strange noises, blowing warm air or repeatedly tripping the circuit breaker, there may be something wrong with your compressor. AC compressor problems should be handled by an HVAC professional.

How do you reset a thermostat?

To reset your thermostat, first check to see if it has a reset button. If it does, simply push and hold it for five seconds. If it doesn’t, shut off the circuit breaker supplying power to the thermostat for 30 seconds to reset it.

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