Why Is My Air Conditioner Not Cooling Below 75? [10 Causes Included]

The air conditioner is the primary reason why we are no longer afraid of scorching summer days. But it could be very frustrating if you have one that isn’t pulling its weight and can’t cool your house below a certain temperature, like 75 degrees.

If you are facing the same issue, I have the answer. This post summarizes 10 common causes of an air conditioner not cooling below 75. More importantly, the solutions are also provided.

Simply put, dirty air filters and condenser coils are often to blame when your AC can’t get colder than 75. But low refrigerant levels or leaky ducts can also be the culprits. Of course, there are also other possible reasons.

You can use this article as a guide for troubleshooting your faulty air conditioner. Chances are, you can get your air conditioner to cool properly again very soon.

So let’s dive right in!

1. Dirty air filters

dirty ac filter

Although an air filter is a minor component of an air conditioner, it can cause a variety of HVAC issues. When I noticed my air conditioner wasn’t working properly, the first thing I did was clean the filter.

The air filter sits in front of the evaporator coil, which is in charge of removing contaminants in the air. Over time, it can get clogged and limit the airflow. 

When airflow is obstructed, it can cause a variety of problems, including a frozen evaporator coil and compressor overheating. These will impair your machine’s cooling performance, preventing it from cooling the house below 75 degrees.

How to fix it?

Luckily, it is easy to fix. All you need to do is remove the filter, rinse it under running water, and allow it to dry before putting it back. You can also choose to replace it with a new filter.

2. Filthy condenser coils

Air conditioners, as you may know, do not produce cool air. Instead, it lowers the temperature of the room by removing heat from the air. The condenser coil is the component responsible for transferring heat outside.

Because it is exposed to the elements, twigs, brushes, feathers, or debris may fall into it and obstruct the heat transfer process. If this occurs, your air conditioner will be unable to remove heat as effectively, as usual, making it more difficult to cool to the desired temperature.

How to fix it?

Take a look at the condenser coil in the outdoor unit. Remove any visible debris attached to it. 

3. Refrigerant leak 

refrigerant leak

Every air conditioner requires a certain level of refrigerant. Otherwise, the compressor will overheat and stop cooling the air.

When the refrigerant level drops, it frequently indicates a leak in the coil because the refrigerant remains untouched under normal conditions.

How to fix it?

I know you may attempt to fix it yourself, but it is not allowed. Because refrigerant is toxic, it should be handled by a certified HVAC technician. 

They will locate the leak, fix it, and recharge your machine.

4. Faulty thermostatic expansion valve

Occasionally, the low refrigerant level is not caused by a refrigerant leak but by a malfunctioning thermostatic expansion valve.

When this valve fails, less refrigerant enters the evaporator coil, reducing the cooling effect. As a result, the temperature in the room can’t fall below 75 degrees.

How to fix it?

As with the problem above, you should leave it to a certified HVAC professional. 

5. Undersized air conditioner

For those who just installed a new air conditioning system, the wrong size could be the reason why your AC won’t cool below 75. 

Because the hot air will continue to sneak into the space, the room temperature will not fall if the air conditioner can’t remove enough heat in a certain timeframe. 

That is to say, an undersized AC can’t cool down the room even if it works hard and long. 

How to fix it?

Frankly, your best bet is to get a larger AC. The HAVC experts should perform a Manual J calculation to decide the right size for your AC. 

If you are not in a position to purchase a new unit, you can try to turn on a ceiling fan or close the curtain to block the heat to some extent.

If you have a portable AC and it is not cooling properly, you can relocate it to a smaller room. 

6. Extreme weather 

Are you concerned about having to replace or repair your air conditioner? Maybe your air conditioner can cool the house properly again the next day.

When your local area is hit by the unheard-of heat weave, your air conditioner can’t keep up with the increased heat. So it will take much longer to reduce the temperature.

In other words, because of the high outdoor temperature, your system temporarily becomes undersized.

How to fix it?

You can wait until the extreme weather passes because these days are out of the norm. You can also use a ceiling fan and a dehumidifier to make your room feel cooler.

7. Leaky ductwork

As a central air conditioner owner, there are a few more things to consider. Except for the machine itself, the ductwork can also play a role in whether or not it can cool a room to 75 degrees or other set temperatures.

If the ducts are leaking, the cool air can enter more spaces, such as the attic or crawl space, reducing its ability to cool your room.

How to fix it?

You can try to seal the duct on your own if you can find the leak. If you lack the necessary experience, you should contact a professional. They can conduct a thorough examination and may discover additional problems.

8. Poor duct design

Apart from leaks, improper duct design can also affect the cooling performance. This will cause the cool air can’t disperse evenly to rooms, resulting in hot and cold spots in the house. That is to say, some areas will be below 75 degrees, but others are not. 

If you’ve recently moved into a new home, this is most likely the root cause you’re looking for.

How to fix it?

Unfortunately, you should contact the local contractor and ask them to redesign the duct system.

9. Malfunctioning thermostat

faulty thermostat

Picture this: you’ve set the thermostat to 74, but it reads 78. Meanwhile, you feel the room is not as cool as usual. 

While it is possible that the problem is with your air conditioner, it is also possible that something is wrong with the thermostat.

Your thermostat may require a recalibration so that the AC can reach the right temperature. Or its batteries are running low and can’t send the right signal to your system.

How to fix it?

First, you should change the batteries. When this solution doesn’t work, you may need to replace your thermostat.

10. Your air conditioner is too old

Like any electrical appliance, an air conditioner has a certain lifespan. When your air conditioner starts to age, its performance will decrease accordingly. 

If your air conditioner has served you for more than ten years, perhaps it just reaches the end of its life.

How to fix it?

Rather than paying money to repair it, you can get a new model. There is a high likelihood that it will save you more on electricity bills.

Sum up 

The whole point behind an air conditioner is cooler air. When it can’t cool your house to a certain temperature, you will be depressed.

If your air conditioner is not able to cool below 75, you should first clean your machine and then inspect the leaks. These are easy to fix. However, an undersized machine or improper ductwork design can also cause this issue, which should be solved by a professional.

Hopefully, this guide has helped you figure out why your AC can’t cool below 75 and what steps you should take next.

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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.