Air Conditioner Not Cooling? Quick 13 Fixes to Try Now

Whenever the hot days come, your air conditioner sure gives you problems. If your air conditioner is not cooling but the fan is running, what’s the problem and how can you identify and fix it?

To start, the most common cause of air conditioner not cooling a wrong thermostat setting. Then, other common reasons why air conditioner not cooling is a fault capacity and compressor, dirty air filters and coils, electrical faulty and also, a refrigerant leak.

No matter what’s your air conditioner type (window, portable, central, mini split), the problem with air conditioner not cooling is more or less the same. So, try the following fixes.

  1. Set the temperature to 70°F
  2. Change to cool mode
  3. Replace the thermostat
  4. Spin the fan blade
  5. Fix the electrical
  6. Replace the capacitor
  7. Replace the contactor
  8. Unclog the drain line
  9. Clean the air filter
  10. Repair the fan motor
  11. Unblock the vents
  12. Top-up the refrigerant
  13. Upgrade the system

Most of the fixes you can do-it-yourself such as replacing a part and cleaning. However, for some of the items you might want to get a professional to help like compressor faulty and electrical issues. Nonetheless, here are some of the details on how to identify and perform the fix.

Wrong Thermostat Setting – Mode & Temperature

The most common cause of air conditioner not cooling is a wrong thermostat setting or a faulty thermostat / remote controller. This is the easiest way to troubleshoot your air conditioner right away.

  1. Check the temperature setting and set it to 70°F.
  2. Check if the air conditioner mode is set to cool mode or not.
  3. Press the mode button to change it to cool mode.
Cool Mode Symbols

Fan mode and dehumidify mode will not cool as much as cool mode. The thermostat or remote controller needs to be set to cool mode in order for the air conditioner to cool properly.

Wait for 5 minutes and see if your air conditioner is cooling now. If not, change the fan setting and see if the airflow has any difference. If your air conditioner is not responding to the setting, the thermostat or remote controller is probably broken. So, get it replaced and try again.

Faulty Condensing Unit – Airflow, Fan Motor & Capacitor

Another common cause of air conditioner not cooling is a faulty condensing unit or compressor. This is also very easy to check. The condensing unit is located outside your house.

  1. See if the condensing unit is running.
  2. Check if anything is blocking the airflow.
  3. Check if the fan is running and blowing hot air.
  4. Is the fan running oddly slow?
  5. Check if the compressor is running based on the compressor noise.
  6. Is there any abnormal noise?
  7. Take a closer look at the coil. It is very dirty?

Immediately, if you don’t see the fan spinning at all, try to use a stick to give the fan blade a push in both directions. If it won’t budge, check the disconnect switch and see if the fuse is burnt. Also, check your house’s AC circuit breaker to see if it is tripped.

AC Condensing Unit Disconnect Switch

If the fuse is burnt or the circuit breaker is tripped, a lot of things can go wrong and you should get a professional to check it out. It is not safe to DIY and force it to run now.

Next, the condensing unit must be well-ventilated. Anything blocking the airflow will result in not cooling. Also, the fan should be spinning very fast. If not, the capacitor may be broken or the fan motor is malfunctioning. In this case, you need to test it out and get it replaced.

AC Capacitor

If you don’t hear the compressor noise or don’t feel the hot air, that means the compressor is not running and thus, not cooling. So, open up the condensing unit and check for any loose wires. Then, check if the contactor can close. Else, get it replaced.

However, if the compressor doesn’t seem to operate no matter what. It is time to get a professional to check it out. Maybe you need to replace the compressor.

If you found the condenser coil and fan blade very dirty, clean it up and you should feel the air conditioner is cooling afterward.

Faulty Drain Line – Condensate Pump & Overflow Trip

If the condensing unit seems to be normal but the compressor just won’t start, try to check the air handler side and see if the condensate drain is clogged or overflowing.

  1. Check the condensate drain line at the air handler.
  2. Look for the condensate pump and check if it can work.
  3. Check if there is an overflow in the EZ trap.
  4. Clear the clog and see if the air conditioner is cooling now.

Some air conditioners have a condensate water overflow protection where the compressor will stop running if the condensate pump malfunction or the EZ trap is clogged. This can be fixed by replacing the condensate pump or clearing the clog in the drain line.

Dirty Air Filter & Coil – Low Airflow & Frozen Coil

If your air conditioner has a very dirty air filter, the evaporator coil can be very dirty as well. Consequently, the airflow will be lesser than before. So, your air conditioner won’t be cooling as much as before. In addition, you may find your refrigerant pipes freezing up. That’s a clear symptom of low evaporator airflow.

So, clean up the air filter and check if the evaporator coil needs cleaning as well. After that, see if the airflow is back to normal and your air conditioner starts cooling properly.

Weak Fan Motor – Spinning Slowly

A malfunctioning fan motor will spin slowly and thus, deliver less airflow. When there is not enough airflow, your air conditioner won’t be cooling as much as before.

If you’ve checked the air filter and evaporator coil and they seem to be just fine but the airflow is still less than before, then the evaporator fan motor may be weakening and needs to be repaired or replaced.

Airflow Obstruction – Dusty Duct & Blocked Registers

After many years, ducts can get very dusty inside. Some registers or vents can get completely blocked by dust and dirt. As a result, the airflow is lesser and so does the cooling.

Dirty Return Vent

If your air handler seems to be working just fine, you might want to check out the registers and vents to see if they’re blocked. Check the return air grille and see if it is dirty. If possible, climb up and check the condition of the flexible ducts. If they’re very dirty or torn, get them replaced.

Refrigerant Leak

It is possible that your air conditioner is low on refrigerant due to a minor leak somewhere in the pipeline. When your air conditioner is low on refrigerant, it won’t be cooling as much as possible despite having enough airflow.

So, check if the air coming out of the registers or vents are as cold as before. If you feel that it is significantly less cold than before, your air conditioner may be low on refrigerant.

Undersized Air Conditioner

An undersized air conditioner will not have sufficient cooling capacity to handle a big house. On normal days, the air conditioner can provide adequate cooling but during hot days, it won’t be cooling.

If you’ve checked everything and now suspect your air conditioner is undersized, try to use the rule of thumb to check. Take the cooling capacity of the air conditioner (BTU) and divide it by the total floor area of your house (square feet). Usually, you’ll end up with around 20-30 BTU per square foot. Otherwise, your air conditioner may be undersized.

However, before you conclude, try to remember if your air conditioner was working fine all the while and just got warmer recently. Maybe it is just too hot outside and your air conditioner is struggling. Even an adequately sized air conditioner can struggle during exceptionally hot days.

To improve the situation, make sure to close all windows and doors, and set the temperature to the lowest and fan to the highest. Wait it out and see if your house gets colder later.


When an air conditioner is not cooling but the fan is running, the most probable cause is a wrong thermostat setting followed by a fault capacity, a faulty compressor, dirty air filters and coils, electrical faults and even a refrigerant leak.

To prevent your air conditioner not cooling during the hottest period, make sure to conduct regular maintenance such as filter replacement, coil cleaning, fan blade cleaning and top-up refrigerant when necessary.

Many times, air conditioner not cooling is caused by simple problems and it can be fixed in no time with little to no money. Hope you get back to cooling asap!

Lastly, consider my Mini Split (eBook) if you want to know how can you use Mini Split in your house. If you still have doubt or not feeling confident enough, feel free to consult me.

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Ask me for HVAC advice such as brand selection, best model, benefits, features, placement, duct size, grille size, how to design, design check, verification and other HVAC related queries.

If you have anything to add (or ask) about this topic, leave a comment down below!

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