Why AC Is Not Cooling? 3 Troubleshooting Steps

Discovering on a hot day that your AC is not cooling is definitely one of the most unpleasant things out there.

Your air conditioner can stop operating correctly if the thermostat settings are wrong, the air filter is dirty, the outdoor unit is clogged, the evaporator coil is frozen, there is a refrigerant leak, the ducts are leaky, or if the compressor has gone bad. An undersized AC will also fail to cool your house efficiently.

Find out what caused your cooling unit to stop working and what you can do about it.

Why AC Is Not Cooling?

There might be quite a few reasons why your air conditioning unit is failing to cool the house:

Incorrect thermostat settings

The first thing that you need to do is check the thermostat. The device might be set to ‘heat’, for example, or the temperature setting might simply not be low enough for the AC to kick in. 

A dirty air filter

A clogged filter can block the airflow which, in its turn, will reduce the unit’s cooling capacity or make it shut down altogether.

The outdoor unit is clogged

If you have a regular air conditioner with an indoor and an outdoor unit, then you would have to check from time to time if the condenser (the outside part) is blocked with dirt and grass.

Read: Does Closing AC Vents Save Electricity?

A frozen evaporator coil

If the evaporator coil is frozen, the cooling capacity of the unit will be decreased as the air traveling over the coil won’t get cooled.

A refrigerant leak

Minor refrigerant leaks can cause your AC to stop blowing cool air. If the issue gets worse, the whole system will shut down or the compressor will get damaged. 

An undersized unit

It is extremely important to properly size your heating and cooling system. An undersized AC simply won’t be able to bring the temperature in the house to the desired setting as it’s not powerful enough.

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Leaky ducts

Finally, the problem might be not with the actual cooling unit, but with the ducts. If the ductwork has gaps and is not sealed correctly, then a huge portion of the cooled air wouldn’t be able to make it to your room. 

Read: Are HVAC Service Plans Worth It?

What Can Cause an AC to Stop Cooling?

Your air conditioner will not be cooling if it has no power. So, you might want to start the troubleshooting process by checking the circuit breaker and the AC’s on/off switch.

The AC will also stop cooling if the motor or the compressor goes bad. The former is responsible for the unit’s fan, while the latter, under normal circumstances, manages the flow of the refrigerant. 

Why Is My AC Running but Not Cooling?

  • There are issues with the thermostat
  • Something is blocking the airflow (a clogged filter, for example)
  • The evaporator coil is frozen
  • There is a refrigerant leak
  • The fan motor or the compressor is faulty
  • The AC unit is undersized
  • Your ductwork has a leak

Why My Split AC Is Not Cooling?

  • Your split air conditioner might be dirty. This includes clogged filters and a dirty outside component (it can get covered in debris).
  • The thermostat settings might be wrong. If you’re sure that the device is set to ‘cool’, then try lowering the temperature a bit more.
  • A broken or malfunctioning fan motor can cause your split air conditioner to stop cooling (faulty wiring or a short circuit can make the motor go bad).
  • Mini-splits won’t be able to function if they don’t have enough refrigerant in them. A leak will not only make your AC less efficient, but it can also be dangerous for your health, so calling a professional who knows how to handle such substances is the best decision.

Read: How To Do Air Balancing HVAC In A House?

Window AC Not Cooling

  1. First things first, make sure that your window air conditioner is getting power.
  2. The most common reason for a window unit to stop cooling is due to issues with the airflow. Make sure that the filter is clean and examine the part of the unit that is hanging from the window (it might be clogged with leaves and dirt).
  3. Check the thermostat settings and then check the thermistor for continuity. The element is generally located behind the air filter; once you cool the thermistor (by applying an ice cube, for example), the continuity should turn off. If that didn’t happen, then you would have to replace the component. 
  4. If nothing helped, then the chances are high that the control panel, the compressor, or the refrigerant level is to blame. All these issues should be tackled by an HVAC technician. 

Read: Is Closing Vents Bad For HVAC?

AC Stops Cooling After Some Time

If your air conditioner suddenly stops cooling after it has been operating just fine for a few minutes, check the system for the following issues:

  • Faulty thermostat wiring or improper thermostat placing – damaged or loose wires can make your cooling system stop before it reaches the set temperature. If the thermostat is located in direct sunlight or close to a heating source, then the device won’t be able to correctly read the indoor temperature and might end up forcing your AC to turn on and off when not needed.
  • The unit is overheating – the main things that can make your AC overheat include clogged filters and grime buildup on the coils.
  • The air conditioner is too big for your house – in such a case, the unit will be cooling your place too fast and the thermostat will shut the system down prematurely.

Should I Turn Off AC If It’s Not Cooling?

It is actually recommended to turn your AC off if you have found out that it’s not cooling.

One of the reasons why the air conditioner might not be working properly is because the evaporator coil is frozen. If you’re planning on calling an HVAC technician, then turning the system off will give the ice enough time to thaw before the specialist arrives (the technician might not be able to correctly diagnose the problem if the coil is left frozen).

If there is an issue with the compressor or the motor, forcing your AC to continue running can make the problem even worse. The unit might also not be cooling properly due to a refrigerant leak, and you certainly wouldn’t want to be running an air conditioner that is ‘emitting’ this dangerous substance.  

Read: How To Remove And Replace Attic Insulation That Fell Off?

How to Check If AC Is Cooling or Not?

  1. Make sure that the air filter is clean. Remove the vent covers.
  2. Locate the supply and return ducts and turn the AC on (don’t forget to set the thermostat below room temperature).
  3. Find the supply air duct closest to the indoor AC unit and tape a thermometer right inside it. Wait for around 10 minutes and write down the temperature.
  4. Test the closest return air duct in the same way.
  5. In a correctly operating system, the difference between the two readings should be between 16 and 22 degrees Fahrenheit. If it’s smaller, then your AC is not cooling properly.

How Do You Fix an AC That Is Not Cooling?

If your air conditioner is not cooling, then there might be something seriously wrong with the system, and calling a certified HVAC technician is definitely recommended.

With that being said, there are a few troubleshooting steps that you can attempt to take on your own.

  • Check the thermostat settings; make sure that the device is set to ‘cool’ and that the fan is set to ‘auto’
  • Replace the air filter, if it’s dirty
  • Clear the area around the outdoor unit
  • Inspect the ducts and seal any leaks
  • Clean the coils


There are quite a few reasons why your air conditioner might not be cooling. 

Improper thermostat settings, airflow issues, a frozen evaporator coil, leaky ducts, a refrigerant leak, a malfunctioning compressor or fan – the chances are high that one of these things has caused the issue.