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If your AC is running but you’re not getting that cooling experience, the problems can range from simple user controls to faulty internal equipment. It is best to take an organized approach to detect where the problem is.

This article features possible problems that can lead to an air conditioner not cooling along with some related solutions.

At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.

Possible reasons for your AC not cooling

1. Check the Thermostat Controller

One of the various reasons your air conditioner isn't cooling could be a problem with the thermostat controller. Most air conditioners, especially portable or split units, come equipped with remote controllers for added convenience. Air conditioners can also be hooked up with your home’s thermostat to synchronize them with HVAC systems’ operation.

The good part about a cooling malfunction related to a thermostat is that it's easily remedied. Here are some issues with the thermostat or the controller that can interfere with your AC's cooling: 

Temperature Sensor

Some air conditioners have a temperature sensor affixed in the controller as opposed to the unit. Dropping the remote too often, water spillage and other issues can dislodge or damage the sensor. 

Temperature sensors for your thermostat are also either built-in or fixed at particular points in your home. If they malfunction, the air conditioner won’t be able to maintain the desired temperature because it is, technically, running blind. 

You can compare your remote/thermostat’s reading with a digital temperature sensor to see if there's a discrepancy. If the readings don't match, you'll likely have to order a new remote to fix the cooling concern. 


If your AC is connected to a smart programmable thermostat, you’ll either have to manually program your schedule into it, or it’ll pick that up itself through learning mechanisms. Either way, this programming will decide when your AC needs to turn on/off, how high or low the temperature goes, etc.

If you haven’t programmed the thermostat properly, your AC will not cool according to your needs. Check the interface on the thermostat to see if that’s the case. The user manual will help you through the interface.


Drained batteries or the wrong polarity setting can also be a concern with temperature controllers. Flip the remote and open the battery compartment to see if the batteries are installed correctly

If that doesn't work either, change the batteries and try again. Dead batteries are a common issue for AC remotes. 


If you’ve connected your AC to an HVAC system, you probably have a thermostat to control it. Modern thermostats come with detailed wiring to control more complex and efficient systems, which is great for your energy bill and comfort, but the wiring needs more attention.
Check what kind of a thermostat you have and if all the wires are connected to the right terminals. You can seek help from the user guide, our wiring guides, or call a technician.

2. Check the Evaporator coils

At times, a problem with the air conditioner's evaporator coil can affect its cooling. Evaporator coils in air conditioners help absorb the heat from your indoor air space and are often located in the air handler's interior or are attached to the furnace. 

An air conditioner's evaporator coil includes evaporated refrigerant that helps the coils absorb heat when the blower fan passes air over them. 

Disadvantages of poorly maintained coils

 If the evaporator coils are dirty, this can interfere with the AC's ability to absorb heat from a given space, and that ends up affecting the unit's cooling. Three danger signs that your evaporator coils need cleaning include the AC not cooling, running for longer cycles, and frost developing on the coils during operation. 


You can choose to clean the evaporator coil in one of three ways: through compressed air, medium-bristled brush, or commercial cleaners. However, be sure to do proper research on how to go about cleaning the coils before settling on the cleaning method of choice. 

3. Check the Compressor

Remember how we said the air conditioner's evaporator coils help absorb heat? The coils can only absorb heat once the compressor compresses the refrigerant and pumps it through the system. That makes the compressor sort of like the brains of your AC – there's no cooling without it. 

That also means that a problem with the compressor will directly impact your air conditioner's ability to cool. What's more, when it comes to compressors, the quicker you can detect the problem, the better it is. That's because compressors can be costly to repair. 

Common Issues

Some of the most common concerns for compressor breakdowns are dirt on evaporator coils, blocked suction lines, inadequate refrigerant levels, contaminant build-up in the compressor, or electrical problems. Low levels of lubricant oil can also cause problems for a compressor. 


Unless you are a pro, it is not wise to DIY a compressor problem. The best course of action is to get in touch with a reputable HVAC firm to help you out.

4. Check the Air Filter

Air conditioners work by sucking out the heated air from a room, running it over coils with refrigerant, and blowing the chilled air back into the relevant space. 

Function of the air filter

An air conditioner relies on air filters to trap airborne particles and maintain indoor air quality. Air filters also help keep dust and grime from building up on the evaporator coils and blower fan. 

That's why dirty filters can affect the way your AC functions and end up reducing its cooling capacity because it has to work harder to push air through the dirty filters. 


Fortunately, most air conditioners have reusable and washable air filters that you can clean by vacuuming and washing. To do so, refer to your air conditioner's user manual to locate the filters. 

Make sure to turn off the AC's power supply before opening the indoor unit's flap to detach the filters. 

From then on, it's just a matter of cleaning the dirt built up on the filters, drying them, and placing them back in their location.

5. Check the Refrigerant

Another common culprit in air conditioners that don't cool is a refrigerant leak. If you're not aware of what refrigerant is – it's a chemical substance that's primarily found in a gaseous or liquid state. 


Refrigerant helps the copper coils of the AC absorb heat as it moves through the system as a low-pressure gas and then a high-pressure liquid. The compressor and evaporator coils send the refrigerant to the blower fan, where heat is extracted from the system. 

Once the refrigerant cools down and travels back as a low-pressure gas, it helps the cool coils blow chilled air inside a space via another fan. This cycle works continuously to keep your preferred indoor temperature maintained. 


Sometimes, the lines transporting the refrigerant can rank due to fluctuating temperatures and wear and tear. When this happens, the refrigerant starts to leak and ends up affecting the entire cooling cycle. Hissing sounds, frozen coils, and loss of cooling are three sure-shot signs of a refrigerant leak.

6. Check the Ducts

Ducts are responsible for transporting chilled air inside your room while at the same time expelling the warm air outside. They're another essential component of an air conditioning system and possible concern behind your air conditioner's cooling woes. 

Blocked air ducts mean that air that should enter or exit a room isn't being adequately expelled – adding pressure on your air conditioner to work harder to maintain your preferred temperature setting. 

Air ducts can become clogged over a period of time if they aren't cleaned or maintained. The best way to ensure your duct system is working as it should is to get in touch with a skilled HVAC technician and schedule a cleaning asap.

7. Is the Unit Size correct?

Buying an air conditioner that can't cool a particular space because of capacity is a mistake that's still pretty common. When you're buying an AC, getting the right size is crucial to ensure ample cooling. 

Cooling capacity and Size

By size, we're referring to the appliance's cooling capacity (measured in British Thermal Units or BTU) instead of its physical dimensions. Your air conditioner's cooling capacity has to match the area size it's intended to cool. If the AC is too large, you'll have high energy bills for the same amount of cooling. Conversely, if the unit is too small, it won't provide adequate cooling. 

To get a rough estimation of the cooling capacity required for your room, multiply the length and width of the given space. Then multiply that total with 25 BTU. For instance, if your room is 16 feet long and 13 feet wide, you'll end up multiplying 208 by 25, which equals 5200 BTU.

8. Central Air Conditioning Problems to consider

Central air conditioning works in steps to ensure uniform cooling throughout the building. The air handler and the condenser are a bit different than split systems or conventional ACs.

Air Handler

A central air conditioner utilizes an air handler or furnace to absorb warm air from your indoor environment via ducts. Then the air is moved past the evaporator coil (generally placed above a furnace in central ACs) filled with refrigerant to cool it down. 


Next, the refrigerant is pushed to the condenser – a component located outside the house that helps expel hot air into the environment. Once the refrigerant is cooled down, it's moved inside to help with blowing cool air inside the house. 


There are quite a few components that make up your central cooling system – but a problem with even one of these components can throw the system's cooling off. 

For example, a build-up of dirt on the condenser, evaporator coil, ducts, or compressor has the potential to affect your AC's cooling. Other problems also include tripped breakers, dirty filters, compressor breakdown, etc.

However, it is also equally possible that your air conditioning problems are related to minor concerns like faulty temperature sensors, wrong programming presets, or thermostat settings. 

 It is also extremely important that you have your system cleaned and maintained to avoid costly issues. When it comes to HVAC, the sooner a problem (no matter how minor) is taken care of, the better it is. 

Common Questions Relating to AC Not Cooling

Why is my air conditioner running but not cooling the house?

When it comes to an air conditioner that's not cooling, there's no such thing as a one-size-fits-all answer. That's because there are certain variables to consider. 

For example, the kind of unit you have, how often you get your air conditioner serviced, the size of the AC in comparison to the room it's cooling, etc. 

Then there's the fact that an air conditioner has quite a few running parts, and all of them are pretty important to cooling. 

So, a problem with controllers, compressors, evaporator coils, condensers, blower fans, suction lines, ducts, filters, etc., can all be possible reasons why your AC isn't cooling.

The Verdict

While AC maintenance and repairs can be tedious, it is best to not put them off. Ignoring a problem with HVAC equipment can snowball into a much bigger predicament. To stay on top of maintenance and get your AC regularly checked by a professional (ideally once a year).


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