air conditioner not cooling

Air Conditioner Not Cooling? Here’s Why (and How to Fix it)

The last thing you want during the summer is for your air conditioner breaking and not cooling properly. You would know right away that there’s something wrong with your air conditioning unit when it’s no longer giving you the right level of comfort. When this happens, it’s time to see if it’s something you can fix yourself or if it’s time to call an AC technician.

So why is my air conditioning not cooling? If your air conditioning is not cooling, it can be due to any of these common reasons:

  • Undersized unit
  • Dirty coils
  • Clogged air filter
  • Faulty compressor
  • Insufficient coolant
  • Ice buildup
  • Faulty thermostat
  • Clogged drain
  • Fan problems
  • Unit degradation due to age 

Some of these problems are easy to fix yourself, meaning you won’t need to call the dreaded AC repairman. However, how do you troubleshoot, how do you fix the problem on your own, and when is it time to throw in the towel and call a professional?

In this guide, I’m going to answer all of those questions and teach you how to handle the most common AC issues a homeowner might face.

Let’s get to it.

First Things First: Is Your Air Conditioning Unit the Right Size for Your House?

Before you go ahead and check the various parts of your HVAC unit, you need to make sure that it’s the right size for your house. Keep in mind that air conditioning isn’t a one-size-fits-all kind of thing where all you need to consider is your budget. Different sized homes and rooms require different AC sizes too. 

A unit that is too small may not have enough power to efficiently and effectively cool your home. Even if you try to crank it to its maximum setting, your AC still won’t be able to reach the temperature you need to fight off the summer heat. Likewise, an unnecessarily big unit will only translate into higher electric bills.

However, when we talk about AC sizes, we’re not only talking about the physical dimensions. The cooling capacity, which is measured in BTU (British Thermal Units per hour), is what actually matters most. To determine the BTU rating you need for your house, all you need to do is have tape measure handy and perform some basic math.

How to Determine the BTU Rating Your Home Requires

To determine the right HVAC size you need, determine your square footage. Once you know the square footage of the area you want to cool (either a room, set of rooms, or your whole house), use the following guidelines from the United States Department of Energy:

  • 100 – 300 sq. ft.: 5,000 to 7,000 BTU
  • 300 – 550 sq. ft.: 8,000 to 12,000 BTU
  • 550 – 1,000 sq. ft.: 14,000 to 18,000 BTU 
  • 1,000 – 1,200 sq. ft.: 21,000 to 24,000 BTU 
  • 1,500 – 2,000 sq. ft.: 30,000 BTU 
  • 2,000 – 2,500 sq. ft.: 34,000 BTU

You should also consider the height of your ceilings. These estimates above apply if you have standard 8-foot ceilings. If your ceiling height is more than 8 feet (for even just one of your rooms), you might want to make some adjustments to your estimated BTU level.

Sunlight is another factor to take note of. If your home gets extra sunny during the daytime, it’s probably a good idea to opt for an AC unit with a higher BTU level than the above estimates. Alternatively, if your house gets a lot of shade during the day, you can decrease the BTU level.

If your air conditioner has a significantly lower BTU rating than what your home requires, the only true way to properly cool your home is to switch to a higher-capacity AC unit. If this is your issue, feel free to stop reading and just buy a new air conditioner.

However, if your AC has the right cooling capacity (which most do) and it still doesn’t cool your home, keep on reading. It’s time to do some troubleshooting.

Dirty Coils

dirty condenser coils

Your AC has two coils: the condenser coil and the evaporator coil. Over time, these coils get dirtier and loaded with debris causing your AC to become less and less efficient at cooling your home. Your air conditioner will need to work harder to meet your cooling demands, but in time, without cleaning the coils, it won’t be able to catch up. 

Evaporator Coil

The evaporator coil extracts the heat from the indoor air and adds it to the refrigerant, which is a cold vapor circulating through copper tubes in the coil. After the heat energy is extracted by the evaporator coil and transferred through the chilled copper tubing, cooled airflow gets pushed into the supply ducts and is spread throughout the house.  

The evaporator coil is always exposed to airflow circulated by the AC’s blower, so it’s prone to the build up of dirt and dust. It’s normal for airborne dust and dirt particles to form a layer on the surface of the coil, and when this happens, the transfer of heat from the air to the refrigerant becomes less efficient. Not only will this result in poor cooling performance, but also higher operating costs since the system runs longer cycles to meet your temperature settings.

Mold contamination is also another thing you need to watch out for. Dormant airborne mold spores circulate through your AC airflow and once they touch the coil surfaces that are wet from condensation, moisture activates them, resulting in active mold growth. Mold growth on the evaporator coil surface also negatively affects the transfer of heat, and if you leave it to thrive, mold growth on the coil air passages will eventually block all airflow and shut down your AC system.

How to Clean

In most air conditioners, the evaporator coil is sealed in the indoor air handling unit, but it has an access panel you can remove to see the evaporator coil. You can clean the coil by using a brush, compressed air, commercial cleaners, or mild detergent. For first timers, using a brush is recommended as it’s quite effective and does away with the need for liquids and chemicals. 

Here’s what to do:

  1. Turn your AC off at the thermostat.
  2. Take off the access panel by removing the screws and other fasteners.
  3. Sweep dirt accumulation off using a soft-bristled brush. Scrub with the brush to loosen harder-to-remove dirt. 

These three simple steps just saved you at least $100, which is what an AC technician would charge to come out to take care of it for you. Depending on your DIY prowess, you might want to have your AC unit cleaned and maintained regularly by an HVAC technician though. Worth noting, the service would probably include coil inspection and cleaning too.

Now, if you found mold growth, you probably want to let the AC technician handle it. He or she will use EPA-approved biocides to disinfect your evaporator coil and the condensation drip pan under it.

Condenser Coil

A condenser coil is a long, coiled tube with metal fins on the outside. The condenser coil has a reverse function. If the evaporator coil takes the heat from the air inside of the house, the condenser coil releases heat to the air outside of your home. A condenser is like a radiator, it needs to be clean and free of blockage for it to release air outside.

Since the condenser is found outdoors, it’s exposed to the elements. The surface of the coil will accumulate dust, dirt blown by the wind, grime, and debris such as grass clippings and dry leaves. Good news though: condenser coils don’t generate condensation moisture, so mold won’t be an issue.

How to Clean

Before you start cleaning your condenser coil, take note that some look clean but actually need a thorough cleaning. As a general rule, your AC condenser coil needs to be cleaned twice per year.

Here’s how to do it:

  1. Inspect the coil.
  2. Remove the debris with a coil brush.
  3. Straighten the coil fins using a fin comb.
  4. Wet the coil and coat with coil cleaner.
  5. Wash away the coil cleaner with water.

Don’t have a coil brush, fin comb, or coil cleaner? No worries, you can find them on Amazon.

To keep your condenser coil clean, clear out an area of two feet around your condenser unit. Get rid of all debris and vegetation on all sides to ensure the free flow of air into the condenser coil intake vents. 

Also, turning off the electrical power to your condenser unit once a year and hosing down the coil can help maintain its efficiency. The upper fan grille should also be inspected for any damage caused by objects like fallen tree limbs.

Clogged Air Filter

dirty AC air filter

A clogged filter makes it difficult for an AC unit to facilitate adequate airflow. With reduced airflow, the AC would have a hard time circulating enough cool air to get your home to reach the temperature you set on your thermostat. This could also cause the evaporator coil to freeze up and block all the air. It would feel like your AC isn’t cooling anything down, especially during those hot summer months.

There are, however, air conditioners that feature a built-in mechanism that shuts the unit down in case the filter is clogged. This helps prevent overheating and damage to the motor. 

A good test to know whether your air filter is clogged is to pull it out then check if you can see through it. If you can’t, then it means you need to clean it before putting it back in or replace it altogether. 

If you have pets or if you turn your unit on really often, you may need to change your filter even more frequently. 

How to Clean

The location of your AC’s filter and how to remove it vary depending on your unit’s model. Be sure to consult your owner’s manual for specific instructions on how to find and remove the filter. It’s usually pretty straightforward though. Almost always, it’s located behind the front grille and it should have an access opening at the side or bottom.

Here are a few ways to do it:

  • Gently vacuum the filter using the brush attachment on your vacuum.
  • Wash it with warm water.
  • If the air filter is very dirty, use a mild detergent when you wash it with warm water.
  • Run a little water with baking soda over your filter to remove accumulated odor.

Remember to be very careful not to damage or tear your filter while cleaning it. You’d be surprised how often this happens. In case you damage it while cleaning, don’t put it back in! You’ll need to buy a replacement filter.

Here’s what NOT to do when cleaning your air filter:

  • Don’t clean your filter in the dishwasher. (That should be incredibly obvious, but again, you’d be surprised!)
  • Don’t reinstall your filter while it’s still wet or damp. Dry it out completely before putting it back in.
  • Don’t turn your air conditioner on until your filter is back in place.

Experts recommend cleaning the air filter in your air conditioner every month to ensure unrestricted airflow.

Faulty or Dirty Compressor

faulty or bad ac compressor

The compressor is an essential cooling component of your air conditioning system. It’s known as the heart of your AC unit. It compresses the refrigerant and circulates it through the evaporator coil and condenser coil.

If your AC isn’t cooling properly, the compressor is without a doubt one of the go-to components you must check. More specifically, you need to see whether your compressor requires cleaning or if it’s faulty.

What to Do With a Dirty Compressor

Cleaning the area around your AC’s compressor should be a part of your own regular AC maintenance. You should also make sure to cover it during the winter. Dirt, leaves, and other debris can collect and build up over the year, and these could stop the compressor from running properly. 

While some people clean their compressors themselves others prefer to hire someone to do the job and get the best results. Know yourself. Maybe you can do it, and maybe you can’t. Even if you can, maybe you’d rather pay for the convenience of having someone else do it for you. Either way, get it done.

What to Do With a Faulty Compressor

If your compressor is malfunctioning, the cooling cycle will get disrupted or it simply won’t start at all. If that happens, your air conditioner won’t be able to reach your desired temperature. If you suspect that your compressor is busted, you’ll want to replace it by purchasing a new one and installing it. Word to the wise: it’s simply way too much of a hassle to fix the broken one. Don’t waste your time and money on it, just buy a brand new compressor.

The fix: how to replace and install a new AC compressor:

If you’re brave enough to install your own compressor (which I only recommend for truly seasoned DIYers), here’s a video from HVAC School that will show you exactly how to do it.

I know what you’re thinking: “All of that’s great, but how will I know that there’s something wrong with my compressor in the first place?”

Don’t worry, I got you covered…

Look out for any or all of the following red flags:

1. Cabin temperature is higher than normal.

One of the first signs that there’s something wrong with your compressor is the air conditioner no longer blows cold air the way it used to. For instance, if you set your thermostat to 78 and it’s 88 in the house, your compressor could be the culprit. A busted compressor won’t be able to properly regulate the flow of refrigerant in the AC system, and your AC will not function properly as a result.

2. The compressor makes loud noises when the AC is on.

Another symptom of a faulty compressor is the loud noise it produces when the air conditioner is running. Just like the other parts of the AC that are driven by the engine’s belts, the compressor features a few interior components and has sealed internal bearings that it uses to turn. If any of these interior components break, or if the bearings seize or fail, it would make all sorts of noises. A worn-out, leaking, or seizing bearing gives out a grinding sound or a high-pitched squeal. Be on the lookout for this.

3. The compressor clutch doesn’t move.

If the compressor clutch isn’t moving, it may indicate a problem with your compressor. The clutch is another important component of the compressor as it allows the pulley to engage and disengage from the engine power so that the compressor turns only when it has to. If the clutch seizes, this would permanently keep the compressor activated. If it breaks, the compressor won’t be able to receive engine power. 

As I mentioned earlier, if your compressor really is broken, it’s far more efficient and cost-effective to replace it rather than trying to repair it.

Insufficient Coolant

refrigerant leak in ac unit

If your air conditioner is still not cooling after you’ve checked the filter, compressor, and coils, it could be because it has low refrigerant levels.

Refrigerants or coolants don’t normally get depleted, so insufficient levels of coolant is indicative of a potential leak. Slow leaks can cause coolant levels to gradually drop. 

What to Do in Case of a Refrigerant Leak

Leaks would require a thorough check of the lines. Your AC system should also be recharged so it could start blowing cold air again. Even I’ll admit it on this one, it would be prudent to call an AC technician to do these things if you suspect a refrigerant leak. They understand the complex nature of cooling systems, how to find where the leak originated, and how to fix the leak far better than most of us. They also know about the chemicals involved to bring the coolant levels back to normal.  

Nevertheless, for those even braver than I am, here’s a great video from Goettl & Las Vegas Air Conditioning, Inc. that walks you through how to fix a refrigerant leak.

Repair or Replace?

Depending on how old your AC unit is and how extensive the work involved would be in fixing the leak, you might consider updating your system to a more reliable or more modern one. An AC technician might also recommend an upgrade over a very extensive repair job if, after assessing the problem, he or she believes it would be more cost-efficient and practical. 

Specifically, a system upgrade would be a better option and would make a wise investment in certain circumstances, such as:

  • Your AC system is more than a decade old.
  • Your AC always experiencing recurring problems.
  • Your AC needs fixing and doing it would cost more than you’re comfortable paying.

Ice Buildup

Sometimes, the evaporator coils behind the filter can get frozen and the air heats up as a result. The ice buildup in the coils could block the contact of the air present inside your house with the refrigerant. This will keep the air from getting cool and your AC will fail to dehumidify it. You can counter this by keeping your air conditioner off for 24 hours. 

When ice builds up in your AC, it could also be because you have dirty filters or coils with poor airflow. As such, you should check your filter and coils and try to clean them. Afterward, check if there’s an improvement in the airflow.

Additionally, if there’s ice buildup, you’ll need to run your AC unit with just the fan so that the ice has a chance to melt off. Now, if these don’t solve the ice problem and your air conditioning unit still doesn’t cool your home, the problem could be low refrigerant levels.

Faulty Thermostat

bad thermostat air conditioning not working

If you made sure your filter and coils are clean and everything is good on the power front yet your air conditioner is still not giving you cold air, the problem might be the thermostat not being set to the right temperature. The thermostat monitors the incoming air temperature and then turns the compressor on or off.

Normally, there’s a sensing bulb attached to the temperature control that checks out the air temperature and prompts the thermostat control to run the compressor when your desired temperature is lower than the air temperature of the house. The thermostat also cycles the compressor off when the AC has reached your desired temperature. 

If something is wrong with the temperature control or the thermostat, it may not turn the compressor on. As a result, cooling doesn’t take place. 

What to Do in Case of a Thermostat Issues

Check the sensing bulb for any signs of kink, rupture, or a sharp bend. If you found any, replace the control. But before you condemn the control, you should also make sure that the sensing bulb is correctly positioned in the airflow through the evaporator coils.

You should also inspect the continuity of the temperature control with a multi-meter by turning the dial all the way down to the lowest setting or by pushing the buttons to the lowest temperature. See if that prompts the compressor to run. Lastly, check and make sure all the wiring to the thermostat unit is connected correctly.

Clogged Drain

Air conditioners get rid of moisture from the air and the water normally drains out of a pipe or hose outside. The drainpipe is a safety feature that keeps water from backing up into your unit and from dripping inside the house. However, this drainpipe can get clogged with algae or worse over time. If you don’t clear this out, it’ll eventually cause your AC unit to malfunction and shut down. 

You can clean the pipe with a mild bleach solution and it’ll be good as new.

Fan Problems

air conditioner fan not working

Your air conditioner may have problems with the fan or fan motor if it’s not cooling properly. Normally, the fan draws air over the cold evaporator coils and recirculates it back into your house. However, if the circulating fan is running too slow or isn’t running at all, there will be little or no airflow. That will allow evaporator coils to become too cold, resulting in the formation of frost or ice. This, in turn, restricts the airflow even further.

Both the fan and fan motor are found inside your AC unit, so you need to remove the cabinet in order to check them. Make sure the fan motor can turn smoothly and check the fan blades for damage. If the fan blades are damaged, or if the fan motor is seized, you’ll have to replace them. 

Unit Degradation Due to Age

Let’s face it, air conditioners wear out over time. Just like any other appliance or piece of electrical equipment, your air conditioner’s performance will degrade throughout its usage. Its cooling ability will decrease over time and it’ll utilize more electricity.

In fact, according to the American Society of Heating, Refrigerating and Air Conditioning Engineers, during the first year of an AC unit, there’s a 7% reduction in its efficiency. During the second year, it’s 5%, and every year after that, it’s 2%. This reduced efficiency can peak between 20%-30% depending on the quality. This decline in efficiency can also go as high as 40% for AC units that are at least 20 years old.

If you’re having cooling issues and you have an extremely old air conditioner, it’s high time to replace it completely.

Other AC Cooling Problems

Aside from the issues I mentioned so far, there are other possible reasons why your air conditioner isn’t cooling like it’s supposed to. It could be other defective parts, high atmospheric pressure, a faulty remote control, a blown fuse, or a tipped circuit breaker, as well as other issues.

When troubleshooting, I highly recommend starting with the easiest parts to inspect and clean. If after cleaning and fixing one part and the problem persists, you can proceed to inspect and clean the next accessible part.

Keep in mind that you won’t be able to DIY your way into fixing your AC’s issues all the time. If you suspect something needs to be done other than what you honestly feel you can handle given your level of experience, go ahead and turn the job over to an AC technician. Doing this will save you the time and hassle while ensuring that the issue gets fixed correctly without messing anything else up along the way.

Final Thoughts

In this in-depth guide, I covered a great deal. If you read it carefully, you should now be armed with everything you need to know to: 1) troubleshoot why your air conditioner isn’t cooling, 2) tell the difference between issues you can fix on your own and those you should hand over to an AC technician, and 3) fix the bulk of the problems your air conditioner could be facing.

As always, wishing you much success as well as a cool and comfortable summer!

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