Portable Air Conditioner Not Cooling? 9 Causes + How to Fix

A portable air conditioner has its advantages: you can save on power by using it only when you need it and in the limited space of a room. But, these advantages can turn to naught if your room AC is not cooling and needs to be fixed. So, how do you fix a portable air conditioner that’s not cooling? 

You can fix a portable air conditioner that is not cooling by cleaning dirty air filters, correcting wrong settings on the thermostat, cleaning the condenser coils, defrosting the evaporator coils, clearing a blocked vent hose, or calling an HVAC expert to fix a malfunctioned fan among other fixes.

This article will discuss at length these non-cooling portable air conditioner fixes. Here’s a quick overview of the fixes in the order that you should carry them out:

• Check the portable AC for Wrong Thermostat Setting – Set thermostat setting to COOL.
• Check the Air Filters for Dirt and Clogging – Clean air filters.
• Check the Condenser Coils for Dirt – Clean the condenser coils.
• Check if the Evaporator Coil is Frozen – Allow the evaporator coil to defrost.
• Check the Fan for Malfunction or a LOW setting – Call an expert HVAC/set the Fan to HIGH.
• Check the Vent Hose for Obstruction or Exceeded Length – Adjust the vent hose.
• Check if you have a Full Condensate Tank – Empty the condensate tank.
• Check if the Portable AC is Correctly Sized for the Room – Get the right size Portable AC.
• Check for External Sources of Heat – Eliminate external sources of heat.

Let’s give you details about each of these fixes.

Check the Portable AC for Wrong Thermostat Setting

Portable air conditioners have a MODE option that allows you to choose between 3 thermostat settings: COOL, DRY, and FAN (Reverse cycle models also have an AUTO setting). 

As can be guessed, your portable AC has to be set on the COOL mode to blow cold air. So, if your AC is set on the DRY mode which is meant to control the humidity in your room, or on the FAN mode which allows you to set the speed of your AC fan (High/Mid/Low), then it will not cool.

To troubleshoot, simply press the MODE option on your AC until the green light beside the COOL option is lit. 

With the COOL option set, you can then choose how cool you want the air, which should be set at a level above the room temperature.

Check the Portable AC’s Air Filter(s) for Dirt and Clogging

If your portable AC is already set on the COOL mode but still does not blow cold air, proceed to check the air filters. 

Dirty air filters limit airflow and if not enough air is flowing into your room AC, the evaporator coil can frost over and your AC won’t cool.

If your assessment concludes that the air filters are dirty, clean the portable AC air filters following these steps:

1. Switch off your portable AC and wait a couple of minutes for it to cool.
2. Remove the cover on all the filters (portable ACs can have up to 4 filters depending on the model).
3. Remove the filters from the AC.
4. Wash each of the air filters with warm water and a bit of kitchen detergent. A vacuum cleaner attachment for blowing dirt can also be used if the filters are not too dirty. 
5. Allow the filters to dry completely.
6. Place the filters and covers back in their place and test to check if your portable AC starts cooling.

If your portable air conditioner does not cool, proceed to check other possible causes.

Note: Most portable air conditioners come with standard washable filters that can be reused. But you can opt to separately buy disposable carbon and antimicrobial filters for finer filtering.

Check Condenser Coils for Dirt

The condenser coils in a portable air conditioner are located behind the filters. Their job in the cooling process is to release the hot air from your AC’s cooling process to the outdoor. 

If the condenser coils are covered with dirt, the heat from the AC will not be expelled and will instead stay in the system longer than it should.

What follows is that the little cooling done by your portable AC will be lost in the hot surrounding air. Also, your cooling unit will have to work harder to maintain the required room temperature, which will also be difficult to achieve.

The solution for dirty condenser coils is to clean them. We always advise that you call an experienced AC technician to take care of your dirty condenser coils as doing so requires expert skill.

Also, condenser coils are a costly part of your AC, and once spoilt, the cheaper option is to buy a new cooling unit.

That said, we give you a step-by-step guide on how to clean dirty portable AC condenser coils, which is what the AC expert will do when you call them.

Cleaning condenser coils can be done in different ways, but the simplest and most economical way is to use available home materials as explained: 

1. Switch off the portable air conditioner and wait for it to cool. 
2. Remove the access panel to see and reach the evaporator coils.
3. Use a vacuum cleaner to remove all the dirt that’s stuck on the evaporator coil fins. See how to vacuum evaporator coil fins.
4. Mix a bit of kitchen detergent with warm water and pour it into a spray bottle. It could be the spray bottle you use in your laundry, a DIY option to a coil gun sprayer.
5. Spray the water-detergent solution onto the evaporator coils, leaving a few seconds to soak and loosen the dirt. Apply again as needed.
6. Scrub away the loose dirt with a fin brush or wipe it away with a soft cloth. Be always careful not to apply too much pressure on the fins and bend them as this could block part of the evaporator coils and compromise the airflow. 

If you do not want to use water and detergent, you can also opt to use a commercial product like the Nu-Calgon 4171-75 Evap Foam No Rinse Evaporator Coil Cleaner. This product does not require any rinsing and will protect your evaporator coil fins from corrosion.

If your condenser coils are clean and the portable AC still won’t cool, it’s time to check the evaporator coils.

Check if Evaporator Coil is Frozen

It’s easy to check the evaporator coil while you are checking the condenser coils. Simply assess the top of the compartment that holds the two parts and notice any ice.

During the heating process, the evaporator coil extracts heat from indoor air and delivers it to the refrigerant. If there’s bad airflow across the evaporator coil and the airflow is blocked, the evaporator coil will be frozen. 

A frozen evaporator coil won’t let in the air that needs to be cooled, which is why your AC won’t be blowing cold air.

If your portable AC has a frozen evaporator coil, leave it switched off for 24 hours to allow the coil to defrost. You may need to find an alternative way to stay cool in the meantime. You can, however, accelerate the defrosting process by letting the AC run on the FAN mode. 

Should you assess the condenser coils and the evaporator coil and they are in a good state or you have cleaned/defrosted the coils and still your portable AC won’t cool, your next possible culprits could be the fan or the vent hose.

Check the Fan for Malfunction or a LOW setting

Poor airflow can be caused by issues with a portable AC fan. If your AC fan is set on the LOW option, the cool air may not be sent to the room as fast as it should. 

Also, a portable AC fan may be blocked or damaged. Pointing a flashlight through the grills can help you check to see if the fan is moving and if there any blocks or dirt compromising the fan’s efficiency. 

The first thing you can do to troubleshoot a fan that seems not to work as it should is to ensure the AC fan is set on HIGH. Simply hold down the FAN button until the HIGH mode is selected. 

If your fan is running on high but seems not to blow air as required, have an AC expert work on the fan. Correcting a malfunctioning portable AC fan will require some disassembly, which is best done by a pro. 

You can let us help you connect with a reliable AC pro near you by filling out the form at the bottom of this article.

Check the Vent Hose for Obstruction or Exceeded Length

The cooling process of an AC produces heat that has to be vented to the outdoors. This explains the presence of a vent hose on your cooling unit.

Most portable ACs come with a vent hose that’s 4 to 5 feet long. If it’s longer than this, a vent hose can retain the heat for too long, which means more heat staying around your portable AC.

A bent or obstructed vent can also cause the same issue with retained heat. This heat is also dangerous for your AC’s compressor as it can cause it to overheat and stop cooling. 

To ensure an obstructed or extra-long vent is not making your portable AC not to cool, perform these troubleshooting options:

• Ensure the vent hose is short and straight to prevent heat from building up inside and finding its way back to the portable AC. Consider that a vent hose with bends is worse than a long one.
• Ensure the vent hose has no leaks as this will send some of the heat back to the room.
• Ensure the window bracket is well sealed with no leaks to prevent any of the heat from entering back to the room.

If your portable AC is still not cooling after optimizing the efficiency of the vent hose or the compressor seems to have been spoilt from overheating, call an AC expert to sort you out.

Check if You have a Full Condensate Tank

Most portable air conditioners will show an error code when the condensate tank is full. Since the error code may vary from model to model, you’ll need to check your AC’s user manual to decipher the error code.

Note that some portable ACs also have a hose to drain the condensate directly out of the AC. In such cases, you need to check that the drainpipe is clear and not clogged.

Also, the condensate in your portable AC is more often than not reabsorbed back into the condenser to help in discharging the heat. That means your AC’s condensate tank may not always have water, but if it does and it’s full, the portable AC can jam and fail to cool.

To ensure that your portable AC is not failing to cool due to a full condensate tank, you’ll have to empty the condensate tank then retest the cooling unit.

Here’s how to empty your portable AC’s condensate tank:

1. Switch off the AC and unplug.
2. Remove the vent hose. It will be easier to remove it from the AC’s end rather than the window end. Besides, most models simply require you to slightly turn the hose.
3. Wheel the AC out to a patio or place it on an elevated surface.
4. Open the cap on the spout and let the water run out of the tank by bending the AC backward. If you do it inside, you’ll need a bucket to collect the water.
5. Replace the cap and wheel the AC back to its original position.
6. Replace the vent hose and test if the AC starts cooling.

If your portable AC resumes cooling, great! If not, you are left with the option of trying other causes that may not be directly related to the AC itself but to the surrounding.

Check if your Portable AC is Correctly Sized for the Room

Portable ACs are supplemental cooling units meant to cool medium and small-sized rooms or make up for a cold air deficit from a central cooling system in a bedroom, study room, basement, or other rooms that need the extra cooling.

If your portable cooling unit is used alone to cool a space, it should have a cooling rating enough for the room’s square footage.

Also, as we tell you in the next non-cooling portable AC issue, if your room has plenty of heat from external sources, the cooling capacity of your portable AC will be compromised.

All these situations can make your portable AC appear as though it’s not really blowing cold air. To resolve the issue, ensure that your portable air condition is right-sized for the room.

To determine the right size of portable AC for a room:

1. Calculate the square footage of the room by multiplying its width and length. If you have a room with an extremely high ceiling, you’ll need to factor that too.
2. Use the resulting square footage to find the correct cooling capacity for your room size as indicated on this table by ENERGY STAR.

For example, if your room is 15ft by 35ft, then that is 525sq. ft. (15 x 35), which means your portable AC should have a 12,000 BTUs per hour rating.

Check for External Sources of Heat Affecting your Portable AC

Sometimes, the heat load in your room may be too high for the cool air from your AC to be felt. 

There are several external sources of heat that can render the cool air from your portable AC insufficient: 

• Poor insulation on windows and doors.
• Open doors and windows. 
• Exposure of your portable AC to direct sunlight.
• Other running home appliances that produce significant heat like the stove and oven.

To ensure the cool air from your AC makes a difference in cooling your room, reduce the amount of external heat coming to the room or to the portable AC by doing the following: 

• Insulate your windows and doors.
• Ensure your doors and windows are closed when the AC is on.
• Block direct sunlight from getting to your room using blinds or curtains.
• Go for an AC with a higher cooling rating if there are unavoidable sources of heat in the room.

Always remember that a trial and error approach in fixing a portable AC that is not cooling can be costly if you damage the cooling unit. To prevent this from happening, fill out the form below and we’ll connect you to a reliable pro any time your portable AC has issues to be fixed.

Nicole Sutton

Nicole Sutton is an enthusiastic writer and knowledgeable contributor to TemperatureMaster.com. She offers a plethora of knowledge to the platform, with a background in environmental science and a profound curiosity with all things connected to temperature regulation. Nicole’s interesting and informative writings assist readers in making informed decisions about home heating, cooling, and climate control.