Portable air conditioners are a convenient and efficient way to keep any given space cool during the hot summer months or whenever you need a breath of fresh air. However, like any appliance, portable ACs can encounter problems from time to time.

We are going to explore some of the most common reasons why your portable air conditioner may not be blowing cold air as expected and provide practical solutions to get it up and running again.

So, join me below, and let’s discover the possible culprits behind your warm air woes, as we attempt to figure out why your portable air conditioner stopped cooling.

Why Is My Portable Air Conditioner Not Cooling?

If your portable air conditioner stops cooling there could be several reasons. Your portable AC may have low freon levels or a faulty thermostat sensor.

Additionally, using the wrong size unit for your space can hinder cooling efficiency. Another factor to consider is whether the room is properly sealed. Lastly, a dirty air filter can obstruct airflow and reduce cooling performance.

What To Check When Your Air Conditioner Stops Cooling

By tackling these potential issues, you’ll be able to troubleshoot and find solutions to the problem of your portable AC not cooling effectively. So, let’s take a deeper look.

Your AC Is Low On Freon

It’s not uncommon for portable air conditioners to stop cooling properly due to low levels of freon or refrigerant. When your AC is running low on freon, the hot air that enters the cooling chamber is released back out before it has a chance to cool down to the desired temperature.

While determining if your AC unit is low on refrigerant usually requires professional assistance, there are a few telltale signs you can watch out for.

Keep an eye out for the following:

  • Longer cooling cycles
  • Higher energy bills
  • Frost buildup on AC compressor, vent, or exhaust hose

If you notice these signs, it’s likely that your portable AC is indeed low on freon.


If your AC is low on freon, the quickest way to fix it is to perform a freon recharge.

It is important to note that the United States Environmental Protection Agency (EPA) regulations state that only certified professionals are allowed to handle the task of recharging freon in your portable air conditioner unit since only they have the necessary expertise and knowledge to safely and effectively perform the recharge.

The cost of recharging your ACs freon can vary depending on factors such as the type of freon used and the service provider you choose. It’s worth mentioning that if your AC unit uses R-22 freon, the cost may be significantly higher due to a more limited supply of this particular refrigerant.

In most cases, a freon recharge is necessary when there is a leak in the AC system. This means that it is crucial to address and repair the leak first to ensure your AC functions normally and efficiently once the freon has been recharged.

So, remember that hiring a certified professional is the best way to handle these tasks and get your air conditioner back to its optimal cooling performance.

Faulty Thermostat Sensor

Thermostat sensors are an essential component for the proper functioning of your AC unit. They are responsible for providing accurate temperature readings to the control board, allowing it to regulate the cooling process.

However, if the thermostat sensor is faulty, it can give incorrect temperature readings, leading to your air conditioner shutting off before your room reaches the desired coolness.

This can be frustrating, as it prevents your AC from effectively cooling your space. Therefore, ensuring that your thermostat sensor is functioning correctly is crucial for maintaining a comfortable indoor environment.


If a malfunctioning thermostat sensor could be the culprit, addressing the problem is crucial to restoring proper cooling capacity to your air conditioner. To begin troubleshooting, consult your AC’s owner manual for guidance on dealing with a faulty thermostat sensor.

In most cases, it’s recommended to seek assistance from a professional technician or repairman. Repairs involving thermostat sensors typically require expertise as they are located near the evaporator coils of your AC unit.

Only a qualified technician will be able to ascertain the severity of the issue and determine whether the thermostat can be repaired or if it will need to be replaced.

Make sure you have the right size air conditioner for the room

Wrong Size For The Room

If your portable AC doesn’t seem capable of cooling your room properly, it may be a result of improper sizing. Using an air conditioner that is too large for your room can lead to frequent on-and-off cycles, even when it hasn’t run for a sufficient duration. This can result in a humid and warm environment, leaving you feeling clammy and uncomfortable.

On the other hand, a portable air conditioner that is too small for your room will struggle to reach your desired temperature, working tirelessly but ultimately falling short.

It’s crucial to find the right-size AC unit that matches your room to ensure efficient and effective cooling, allowing you to enjoy a comfortable and refreshing atmosphere.


The cooling capacity of an AC unit is measured in a unit called BTU. If your AC’s BTU rating is either too large or too small for your room, it’s time to consider getting an appropriately sized unit.

To calculate the right BTU for your room, start by multiplying the length and width of the room to determine its square footage. Next, multiply the total square footage by 20 BTU. In other words, every square foot of your room should be allocated about 20 BTU.

To simplify the process, here’s a handy reference list of AC sizes recommended for various common room sizes:

Area to be Cooled (Square Feet)Capacity Needed (BTU per Hour)
100 – 1505,000
150 – 2506,000
250 – 3007,000
300 – 3508,000
350 – 4009,000
400 – 45010,000
450 – 55012,000
550 – 70014,000

For extra-large rooms, those that are 1,000+ square feet, consider getting multiple portable units or consult an HVAC professional for specific requirements.

Bad Air Sealing

Another highly common reason why portable air conditioners stop cooling properly is having improperly sealed rooms.

For example, when doors and windows are left open, they allow hot air from outside to enter your room, undermining the cooling effects of your AC unit. Additionally, this can lead to the escape of the cool air generated by your portable air conditioner.

To ensure maximum cooling efficiency, it is crucial to properly seal your room by closing all doors and windows. This helps to create a controlled environment where your AC can effectively cool the air and maintain a comfortable room temperature.

Keep in mind that even if your doors and windows are closed, bad weatherstripping will reduce the effectiveness of your AC unit.


To effectively address this issue, it is crucial to properly air seal your room. Remember that even small gaps can drastically reduce your AC’s ability to cool the room effectively. Not only can this result in energy wastage, but it will also lead to considerable discomfort for you and your family. 

Taking the time to thoroughly seal any gaps or openings in your room will ensure that cool air remains inside while keeping hot air out. By doing so, you can optimize your portable air conditioner’s cooling performance.

Check the filters on your portable ac unit

Dirty Air Filters

If your portable AC is failing to blow cool air, a likely culprit could be your air filter is dirty or clogged.  Even if your AC unit is operating normally, a clogged filter can hinder its efficiency and effectiveness by restricting airflow, and trapping dust, dirt, and other particles that can accumulate on the unit’s evaporator coils.

To troubleshoot this issue, locate the air filter in your AC unit and check if it requires cleaning. By doing so, you can ensure proper airflow and enhance the cooling performance of your portable AC unit.

Don’t overlook the significance of regularly cleaning or replacing your air filters as it plays a crucial role in maintaining an efficiently functioning portable air conditioner unit. 


Thankfully, while having dirty filters is one of the most common reasons why your AC stops getting cold, it is also one of the easiest fixes on this list.

To begin, remove the filter and use a brush or vacuum cleaner to gently remove any trapped dust and dirt. If your filter is washable, you should rinse it under lukewarm running water to remove any stubborn dirt.

Afterward, allow the filter to dry completely before reinstalling it back into your portable AC.

What If You Can’t Fix The Problem?

If your portable air conditioner unit is failing to provide adequate cooling, it’s worth taking the time to troubleshoot the issue before reaching out to a technician. In many cases, the solutions are straightforward and can be implemented without professional assistance.

However, it’s important to note that there are instances where repairing malfunctions in the internal circuitry or mechanical components of the portable AC units requires the expertise of a knowledgeable tech.

We hope today’s post has shed light on the primary factors that can hinder AC cooling efficiency. If you found this guide helpful, don’t hesitate to share it with a friend in need of troubleshooting tips for their portable air conditioner that has stopped cooling.