Why Is My Air Conditioner Not Cooling? [14 Reasons Included]

On hot summer days, many of us can’t live without a working air conditioner. When the sweltering heat constantly enters the room, it is extremely frustrating to see an AC not cooling the house.

So, why isn’t your air conditioner cooling? In this post, I’ve summarized 14 causes. While a faulty part could be to blame, a lack of maintenance can also have a significant impact.

In this post, I’ll go over each cause of an air conditioner not cooling and show you how to deal with it.

Without further ado, let’s get started!

1. Wrong thermostat setting

wrong thermostat setting

Sometimes, a very simple problem can result in an AC not cooling the house. For example, one of your family members may have turned off the “cool” on the thermostat at night without notifying you.

In this case, you just need to turn on the “cool” again and ensure the set temperature is below the ambient temperature. 

Occasionally, the thermostat can run out of power and can’t send the signal to your HVAC system. The problem can then be resolved by replacing the batteries.

2. Tripped circuit breaker 

Your air conditioning system may not activate if you feel warm air blowing out of the register. Examine the circuit breakers. When your air conditioner’s circuit breaker is turned off, it will not cool the room.

Turning it back on may cause your air conditioner to begin cooling your room again. If it trips again, you must contact a licensed electrician.

3. Dirty air filter

dirty ac air filter

The two causes I mentioned above will result in your air conditioner not turning on and, as a result, not cooling. However, in most cases, your air conditioner is turned on but is unable to cool the room.

The most common of these potential causes is a clogged air filter. The filter will accumulate dirt, dust, and debris over time, reducing airflow and producing less cold air as a result.

A dirty air filter may also cause an ac to freeze up, affecting the performance.

Replace it with a clean filter to see if the problem is solved.

4. Frozen evaporator coil

frozen evaporator coil

The evaporator coil requires air to warm up so that the refrigerant can circulate continuously between the coils.

Because less warm air can enter the machine, clogged air can cause the evaporator coil to freeze. Meanwhile, some grime may adhere to the coil itself, obstructing heat transfer and causing the coil to freeze.

When the evaporator coil freezes, the refrigerant cannot function properly, and your air conditioner may begin to blow warm air rather than cold air.

To allow the coil to thaw, use the “fan” feature or turn off the machine. When the coil is dry, remove the dirt and restart the machine to see if it will work again.

5. Refrigerant leak

If your ac has been used for years, it may utilize R-22 Freon as the refrigerant. Otherwise, the refrigerant is likely to be R-410A. 

Regardless of the refrigerant charged, it can leak. When there is less refrigerant in the coils, lines, and compressor, the pressure will decrease, causing the refrigerant to absorb more heat and the coil to ice up.

Again, whenever the evaporator coil ices up, you can expect your ac not to be able to cool the house as usual. Before fixing the leak, you should check the refrigerant level. Once you ensure the leak happens, ask a pro to locate where the leak is and fix it.

6. Dirty condenser coil

The condenser coil in the outdoor unit, like the evaporator coil, can become dirty over time. When it is obstructed, it can impede the process of transferring heat to the outside, resulting in a lack of cool air.

To remove the dirt and grime, you can use a brush or even a vacuum. It is also acceptable to rinse it with water.

7. Broken fan

The fan is in charge of drawing air into the ac. When it fails, your air conditioner cannot obtain proper airflow and thus cannot keep the room cool.

It’s possible that the fan motor has become clogged due to dirt and dust, but it could also be completely dead.

Because the fan is difficult to access, you should have it cleaned or replaced by an HVAC professional.

8. Vent blockage

You can easily understand why a blocked vent can cause this problem now that you know that limited air flow will cause an air conditioner not to cool.

If your home’s maintenance is neglected, airborne particles will clog the registers over time. You may also unintentionally place some furniture in front of it.

To address it, inspect each vent in your home and clean or remove any items that are blocking it.

9. Your AC is too small to cool your room

You may notice that the air is cold when you place your hand on the vent. However, the temperature in the room does not fall. On this particular occasion, your machine simply cannot cool such a large room.

If your air conditioner is portable, you can move it to another small room where it may work well. However, if you have a central air conditioner, replacing it with a new one may be a better option.

10. Broken compressor 

An air conditioning system’s core component is the compressor. When it fails, the refrigerant loses its ability to circulate and transfer heat. As a result, the air conditioner will not cool. It will instead emit warm air.

Unfortunately, repairing a compressor is expensive. Replacing it with a new one is always a better option.

11. Damaged heat pump 

A heat pump could be used as the outside unit. It functions similarly to a standard air conditioner in that it can both cool and heat the room.

When it fails, which could be due to a problem with the compressor or the coil, your air conditioner will stop cooling the house.

It is difficult to repair a heat pump. You could speak with a professional or the manufacturer.

12. Outside temperature is too high

Although air conditioners provide cool air on hot summer days, they cannot withstand extremely high temperatures.

When it gets too hot outside, the outdoor unit’s protection mode kicks in, preventing it from working.

You can turn it off for a while to see if the temperature will drop and it will start working again. Otherwise, you might have to consider purchasing a new model.

13. Damaged high voltage wire

High voltage wires determine whether or not the condenser located inside the outdoor unit can operate. The outdoor unit cannot function if it is damaged or faulty. The indoor unit, on the other hand, can activate, causing your AC to run, but it cannot cool.

If you lack the necessary skills, contacting an electrician can help.

14. Broken capacitor

broken ac capacitor

It is uncommon, but the capacity can fail. If something goes wrong, the outside unit will also not turn on. This is due to the fact that capacity stores electricity and the unit cannot produce cool air when it is out of power.

The capacitor can be replaced, but only by a qualified HVAC technician.


This post has covered the majority, if not all, of the causes of an air conditioner not cooling.

First, check the thermostat and circuit breaker because it could simply be a bad setting. If they are not the cause, inspect the air filter and coils to see if they are frozen or dirty.

Finally, even though electrical components such as wires and capacitors are not prone to failure, they should be examined.

About The Author

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested dozens of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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