Portable Air Conditioner Troubleshooting (6 Problems & Fixes)

On an unbearable, hot summer day, portable air conditioners can be a game-changer. You will want to troubleshoot the portable AC and get it working as soon as possible when it breaks down. Failing to do so, you will end up with a hefty repair bill and an ineffective cooling device that drains energy like no tomorrow. To prevent all that, this post will address the common issue facing a portable air conditioner and how to fix it promptly before setting a date with an air specialist.


Before we begin, we should acknowledge that portable air conditioners are designed specifically to cool small to medium-sized rooms such as the living room, bedroom, basement, lounge, kitchen, or home office. It may be compact, it holds all the components you will find in the refrigerant air conditioner that needs troubleshooting.

You have an air filter that blocks dust, dirt, and debris from passing through the coils. The aluminum fins evaporator coil with refrigerant fluid captures heat and cools the air. The condenser coil does the opposite by exhausting hot air outside. Stuck in between, the compressor motor compresses the refrigerant agent into a gaseous/ liquid state. A thermostat regulates the AC operational cycle based on ambient room temperature. A compressor fan and AC blower are located at the back. A bottom reservoir collects the excess moisture from the hot air. Lastly, a capacitor stores and transfers energy to the motor.

1. Portable AC Suddenly Stopped Working And Restart

The AC will stop working when the room temperature is reached and restart as the temperature in the room rises higher than the outside. However, there are other possibilities that why a portable would suddenly stop working and restart (short-cycling) prematurely:

  • An active timer stops the cooler from running once the interval time has reached. If that’s the case, just deactivate the timer, and things will be back to normal.
  • A dirty air filter/ evaporator/ condenser/ thermostat could also cause a portable AC to stop working and restart irregularly. Keep it clean from dust, debris, and mold from time to time. Be extra careful not to damage the filter components during the cleaning.
  • A poorly placed AC could be a triggering point for the frequent restart. Move the portable air conditioner to an obstruction-free location for constant airflow circulation. Ensure there are 2-4 feet of space between the AC ventilation and any objects, e.g. sofa, bed, or wall.
  • A wrong size portable air conditioner could also cause it to turn on and off frequently. For example, A small unit with low BTU ratings will struggle to keep a large room size cool. On the other hand, a large unit with high BTU ratings could be overkill in a small room.
  • The last but least known issue is a leaky refrigerant. The signs include a reducing cooling efficiency along with constant water dripping down. Hiring a certified HVAC specialist for refill and repair is your only option.

2. Portable AC Will Not Turn On

First thing first, check if the portable air conditioner is plugged in. You will be surprised that is the number 1 reason it can’t turn on. Next, check the power cord condition to see if it is damaged or frayed. You will need to replace it before continue using it. If there is still no power source, it could be due to a bad wall outlet or trip circuit breaker. Try plugging it into different wall outlets and see if the portable AC can be turned on. Alternatively, use a non-contact voltage tester or a digital multimeter for testing.

The last possibility could be a blown fuse or a damaged electric circuit board due to irregular voltage or amperage. Given the complexity, you will need a certified air specialist or send it back to the service center for repair.

3. Portable Air Conditioner Not Blowing Cold Air

The main reason why a portable AC is not cooling a room is due to the lack of airflow. You will need to restore the airflow delivery rate by fixing the root cause as such:

  • Dirty air filter – Take out the filter and gently vacuum away the trapped dust, hair, debris, and dirt. Let it air-dry completely before reinstalling the filter and resuming the operation. While you are at it, remove any obstacle clogging the air intake and outtake.
  • Closed all windows and doors – It prevents cool air from spacing and hot outdoor air from coming in. Runs at a higher speed for swifter quick air distribution.
  • Bent fins – Straighten it with a fin comb. Do not attempt using your hand.
  • Faulty compressor or capacitor – Open the panel and inspect for bulges, leakage, or cracks. You can also use a multimeter to check on the capacitor listed rating. Unless you are a certified technician, there’s no easy fix to this.
  • Low refrigerant – Get a qualified AC professional to refill or replace the refrigerant. That is the only option.

4. A Wrong Size Portable Air Conditioner

Incompatible room size and high ambient temperature can impact a portable air conditioner’s cooling efficiency. To resolve that, first, measure the room size to get the right size unit with sufficient cooling capacity. Multiply the width, length, and height of the room to get the cubic footage. Find an air conditioner that fits the bill with a matching British Thermal Unit (BTU).

You should also adjust the AC fan speed according to the ambient temperature. If the outside temperature is too hot, a small portable air conditioner will have a hard time cooling the room. We recommend keeping the AC thermostat not more than 10 degrees Fahrenheit lower than the outdoor temperature. Use it only in n enclosed space and keep the portable AC away from direct sunlight.

5. Strong Musty Odors Inside The Portable AC

The musty smell is a clear indication of mold, mildew, or bacteria infesting the AC compressor or coils. The dark and humid conditions promote the growth of microorganisms. It can cause many respiratory illnesses when it is not dealt with promptly. So the first thing to do is take apart the infested component and give it a thorough cleaning. Once done, the next step is to ensure mold and other pathogens will not return. Keep it in a dry place with humidity between 30-50 percent when you are not using it, particularly during the winter season.

If there is a distinctive burning smell with smoke coming out from the appliance, there could be a burned circuit board, capacitor, or compressor. Immediately shut it down, air out the smoke, and send it back for repair.

6. Overheating Issue

Some portable air conditioners are notorious for overheating issues when running all day. This could be due to poor internal design as the generated hot air cannot vent out properly. Check the hose position and remove any blockage that can impede heat from transferring out. Alternatively, leave the AC unit to cool down for 10-30 minutes after hours of running to let the heat exhaust gradually. If the overheating only occurs recently, there could be a leakage or malfunctioned compressor. Get a technician for servicing.

Final Thoughts

Once you have a grip on how the small appliance works, troubleshooting a portable air conditioner is not hard, and you can do it independently. However, prevention is always better than cure. Routinely check and maintain the portable AC, so there's no need to call the air technician. We recommend doing a complete clean-up when the season ends and just before fall starts with the device left dormant for months. Store it away from the sun, rain, and other external elements that could shorten its lifespan. If you play your cards right, you will have a healthy, cooling, portable air conditioner for years to come.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.