Air Conditioner Not Cooling House Below 80? Here Is How To Fix It

How frustrating! It is a sweat day, but your air conditioner won’t cool below 80. How could such a thing happen?

Calm down! This is a common problem and in most cases, you can troubleshoot and fix it yourself.

In this post, I’ll go over all of the possible causes, from simple to complex, as well as potential solutions.

Let’s jump right in!

1. Dying thermostat batteries

Sometimes, the reason why your air conditioner can’t get your house colder than 80 degrees is simple – your air conditioner doesn’t know it should work to achieve that temperature. 

When the thermostat’s batteries run out, it may be unable to send the correct signal to the machine, resulting in a higher temperature than you set.

What to do?

Easy peasy! Replace the batteries and modify the temperature setting to see if the room can get below 80 degrees. 

2. Malfunctioning thermostat 

Apart from dying batteries, other problems in the thermostat, like loose wiring, can also affect your AC’s cooling performance because your AC may not receive the right command. 

What to do?

If you don’t have the expertise, you should leave it to a technician. They will know whether it needs to be repaired or replaced.

3. Dirty filters

dirty ac filter

As an air conditioner owner for many years, I’ve discovered that dirty air filters can cause a variety of problems, including poor cooling performance.

This is because when the air filter becomes clogged, the airflow decreases. Reduced airflow is bad for any air conditioner because it causes the evaporator coil to freeze and the blower motor to overheat.

When this happens, your air conditioner will struggle to reach the desired temperature.

What to do?

Once the filter is cleaned, the problem will be resolved. Fortunately, it is quite simple. All you have to do is take it out, wash it, dry it, and put it back in. If you don’t want to bother, you can simply replace it with a new filter. After all, an air filter is the least expensive component of an air conditioner.

4. Clogged drain line

Just as an air filter will get clogged over time, so will a drain line. When there is too much buildup in the hose, the water flow is obstructed, causing the water to back up and shut off the machine.

The machine will return to work when the water level of the drip pan falls.

Since your AC is not able to work continuously, it won’t cool your house below 80 if the air outside is too hot. 

What to do?

Like cleaning an air filter, you must disconnect the line from your machine, dislodge the slime and gunk in the hose, and then put it back. A helpful tip is that you can pour some bleach or vinegar through the hose to ward off future growth of buildup.

5. Blocked condenser coils

Condenser coils are responsible for heat transfer. If the heat removed by your AC can’t be transferred outside properly, it will affect your AC’s functionality. 

Because the condenser is exposed to the elements, debris, like twigs and feathers, can get into it and block the fins. 

What to do?

Remove the large particles from the condenser after turning off the air conditioner. It is preferable to thoroughly clean the inside of the outdoor unit.

6. Refrigerant leak

Air conditioners work by making use of refrigerant. When the refrigerant level drops, the cooling performance will be impaired. 

Typically, the refrigerant will remain untouched in the coils and compressor. However, due to some reasons, it can leak.

What to do?

When refrigerant is leaking, you can often hear a hissing noise. However, because refrigerant is hazardous to our health and the environment, you cannot solve this problem on your own.

It means you should contact a certified HVAC professional.

7. It is too cold outside

cold outside

As you may know, air conditioners cannot function properly when it is too cold outside because the lubricant thickens and the evaporator ices up.

Running an air conditioner when the temperature is below 60 degrees is not recommended if it does not have a heat mode.

If you use the cool mode in such circumstances – for example, if your room becomes extremely hot for unknown reasons – your air conditioner will not be able to activate or function properly.

What to do?

There is simply nothing to fix. Just run your AC when the outside is warm. 

8. Your air conditioner is too small

Air conditioners are sized in tonnage. The larger the tonnage, the larger room it can cool down. 

That is to say, when the tonnage of your air conditioner is too small, it doesn’t have the capability to cool down your entire house. It will work continuously, but the room temperature will not fall below 80 degrees Fahrenheit.

What to do?

You should have a professional perform a manual J calculation to determine the size of AC required for your home. If your air conditioner is too small, you may need to replace it with a larger one, which can be costly.

9. Leaky ducts

The cooling performance is determined not only by the machine itself, but also by the ductwork it uses to send out the cool air.

When the ducts are leaky, the cool air can get into more spaces, like an attic or crawl spaces. Since an air conditioner can only release a certain amount of cool air in a timeframe, the cool air in your living spaces will decrease. 

What to do?

Leave it to a local contractor if you can’t locate the leak. 

10. Improper duct design 

If you are one of those who just moved into a house and your air conditioning system is new, the duct design could be to blame. 

When ductwork is poorly designed, it can result in a few hot and cold spots throughout the house, causing some rooms to be extremely cold and others to be extremely hot.

Perhaps your living room can reach 70 degrees, but your bedroom cannot fall below 80.

What to do?

Unfortunately, you need to contact a local contractor and ask them to redesign the ductwork. 

11. Your air conditioner reaches the end of its life

Air conditioners are long-lasting appliances, but they will break down at some point. If your air conditioner has worked for more than ten years, maybe it is time to replace it. 

When an air conditioner ages, its performance gradually deteriorates, preventing it from reaching the temperature you set.

What to do?

It’s time for a new air conditioner! While you will have to pay a lot up front, it will save you money on utility bills because models these days are much more efficient.

Sum up 

Until now, I have summarized 11 common causes of an air conditioner not cooling below 80. 

If you want to prevent this from happening again, your best bet is to commit to regular maintenance, making sure the filter and drain line is clean.

Check out this post if your AC can cool your house below 80 but not below 75.

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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 a lot 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.