12 Reasons Your Portable AC Blows Hot Air (+ Fixes)

Last Updated on October 2, 2022

Portable Air Conditioner are great for mobile air conditioning i.e., conveniently movable. In case your portable air conditioner is delivering warm/hot air in summers there can be several reasons for that. It is not necessary that you have to replace your portable AC when it stops working.

It can be trivial problem that can be easily fixed by taking simple measures and convenient replacement. However, sometimes, you may have to call someone to fix it. If you cannot do it yourself, it is still important to know what is wrong with your portable AC so you can decide either to replace or repair.

The most probable reason for your portable AC to blow hot air is less refrigerant. They are hermetically sealed, so most probably low refrigerant is due to leakage in AC lines. Other reasons for warm air from portable AC include a faulty thermostat, leaked vent hose, incorrect AC mode, deprived refrigerant zones, or damaged electronic components.

There is a wide spectrum of issues that may prevent your portable AC to work in the appropriate way. Best is to first look for the issues that you can easily check and resolve and then go for others.

Below I have provided 11 reasons that could be causing your portable AC to blow hot air:

1. Your Portable AC Is Low on Refrigerant

If all of a sudden, your portable AC has started blowing hot air, then most probably it is low on refrigerant. Actually, less than sufficient freon will prevent necessary phase changes required for cooling.

An automobile belt driven air conditioning system reduces refrigerant level with time. Same is not true for portable air conditioners. They are hermetically sealed, and the refrigerant is supposed to stay inside for the lifetime of unit.

This means that if you have lack of refrigerant inside your portable air conditioner it is probably due to leakage. Before charging the portable AC, you will have to detect the leakage. It may or may not be easy to find.

If your portable AC got a hit someplace or you see a bend there it is very likely that there is leak in the same area.

Pro Tips

  • After detecting and fixing the leak slowly introduce refrigerant in small quantities to the suction line.
  • Make sure that you are using the same refrigerant that is compatible with your portable AC.
  • Give time between addition to stabilize the system. You can check out a detailed guide to charging your air conditioner.

2. Air Is Leaking from Vent Hose

Portable ACs reject hot air outdoors by using an exhaust or vent hose. This hose is a necessity for all portable AC, unlike the optional outdoor intake that is only present in dual hose portable AC.

You have to extend the vent hose from portable AC to a window or hole to exhaust. In case your portable AC is not cooling properly, it might be due to damaged exhaust hose. This may be causing warm air to leak inside the living space that is being cooled.

Leaking Air Vent Hose
Photo by: HVAC/R Training Institute


  • Check for leakages throughout the hose, especially at the spots where it is connected to portable AC and window.
  • You can get another vent hose, in case yours’s damaged. Select the one suitable for your portable AC, in terms of dimensions.
  • Also, for convenient installation and connection of hose with window, you may use a window kit. It makes the fixture very simple and easy. I have selected one for you. You can click here to view specifications.

3. Warm Air Is Being Obstructed at Exhaust

Vent hose is a necessity in portable AC, whether it is single hose or dual hose. By principle, hot air has to be rejected out from the air conditioning units, that run on vapor compression cycle. In portable ACs, though necessary, it is more convenient and flexible compared to other types.

Another reason why your portable AC may not be cooling is the blockage of warm air at exhaust. If exhaust hole to outdoors is covered or blocked, then warm air will not be able to reject outside.

As a result, refrigerant will not be cooled properly in condenser coils. This will affect the cooling performance of you portable AC. Air coming out of the portable would be comparatively warmer (not cool enough) if vent hose partially blocks warm air.

Portable AC Vent Hose

Pro Tips

  • Check vent hose of your portable AC from inside for any hindrance or solid objects.
  • Make sure that the open end of hose is not blocked by anything outside the window.

4. You Have Selected Wrong AC Mode

There is a possibility that your portable AC is blowing warm air due to wrong settings selected in the control panel. Give a check to settings on the control panel located on top or side of your portable AC.

In smart portable ACs, this can also be done by using wireless application on your mobile device. Give it a look just to make sure you are using the right settings.

There may be several modes in your portable AC. However, basic modes stay the same in all units. Normally the options are ‘cool’, ‘fan’ and ‘dehumidifier’ or ‘dry’.

In portable ACs that can use reverse refrigeration cycle there will be another option to act as heater.

Portable AC Controls
Photo by: Haier

Pro Tips

  • Make sure that your unit is running on cool mode.
  • Also check that temperature set is lower than ambient temperature. Generally, portable ACs aim to keep the temperature at about 26°C.
  • Also, if your portable AC is running on dehumidifier mode, it will only operate to remove humidity from room air. When you are running your portable AC in dehumidifier mode, it will exhaust heat in the same room.

5. Dirty or Clogged Filters

Another reason why your portable AC is not cooling properly may be a dirty filter. If your filter is clogged, then cool air is blocked. As a result, flow rate delivered by portable AC will be less than required and room will not cool properly.

Portable ACs are designed in a way that filters are easily extractable. The reason is the inconvenience that you will have if you have to open up the entire portable AC to get it out.

Many units have a filter reset indicator that tells you to clean your filter. Your portable AC will not run temporarily unless you do it. In many models, there is a fixed number of hours of operation after which filter reset light will turn ON.

How To Clean Portable AC Filter?

Portable AC filters are reusable and washable. You don’t have to replace it every time it is dusty. It is preferable to wash the filter with lukewarm soapy water. Take care not to damage it.

The way you extract filter out is almost the same in every model with little difference. It is easily doable. Here’s a video to assist you.

6. Portable AC Coils Are Clogged

With clogged condenser coils, refrigerant inside them not cool properly. The reason is that they require an active flow of air through them to expel heat. As a result, you will get lesser cooling from the portable AC.

Thereby, you should clean condenser coils at least once a year to keep the performance of your portable AC intact and maintain its life. Do this early and you will save yourself a lot of money and effort.

How To Clean Portable AC Coils?

Not every portable AC will give you access to the condenser coils. But in case it does you may clean them by using a soft brush. Clean the condenser coils with gentle upward and downward motion. Get rid of debris and dirt.

Clean carefully as the condenser coils are very fragile. In case you physically affect the condenser coils performance of portable AC will be compromised. Refrigerant may leak out and the only solution may be to change the condenser coils.

Pro Tips

  • Try to keep plants and foliage away from the portable AC. Keep them away from the intake hose in case of dual hose portable AC to prevent getting your condenser coils clogged.
  • In case condenser coils are not easily accessible, you may vacuum through the holes on top of the housing of condenser coils.

7. Your Portable AC Thermostat Is Not Working Properly

A thermostat in an AC is a device responsible for regulating the desired temperature in your living space.

When you select a value of temperature in the control panel, your thermostat will make sure to stop cooling operation after that temperature is achieved.

However, if you have a faulty thermostat, it will detect incorrect temperatures.

This can result in two situations: AC does not turn OFF at the selected temperature, or it turns OFF before reaching that temperature.

Warm air coming out of your portable AC would be an indication for the second situation i.e., the thermostat is turning off before the selected temperature is achieved.

If this diagnosis for your portable AC is correct, you can either calibrate the thermostat or replace it (more about it in the next section).

Pro Tips

Try selecting a temperature in the AC control panel lower than required. If your portable AC starts giving cool air, its thermostat might be sensing wrong temperature.

You can read the manual, or simply contact the manufacturer, to get information for calibration or replacement of your portable AC thermostat. Usually, in terms of design, they are pretty similar in portable units.

8. Blower Wheel or Wheel Motor is Faulty

Condenser blower wheel is the component of your portable AC that actually drives air over Portable AC coils. It is rotated by a motor to suck air from the environment. Heat is rejected to the air and delivered outdoors through vent hose.

If an object makes its way to the condenser blower wheel, it will shatter the blower wheel. As a result, despite the rotation, blower wheel will not be able to suck air and the refrigeration cycle will be compromised.

Condenser Blower Wheel
Condenser Blower Wheel | Photo by Jon HVAC

If you checked other components of portable AC and still can’t figure it out give blower wheel a check.

You can take off the vent hose and look at it. Start the unit and you will be able to see the rotation. Put your hand over the vent and notice the outwards flow of air.

Pro Tips

  • Check temperature at intake and vent. There must be a sufficient difference between them. If they are very close to each other, this means heat is not properly rejected by condenser coils. One reason for that could be faulty condenser blower wheel.
  • Estimate flow of air by keeping your hand in front of exhaust hose.
  • If the blower wheel is intact, but it is not rotating, it may be due to faulty motor that drives the blower. It is way easier and cheaper to get, compared to blower turbine.

9. Accumulated Refrigerant Due to Portable AC Laid on Back or Side

If the portable air conditioner was placed tilted on back or side in the storage it is more likely that it blows hot air. The reason is accumulation of refrigerant inside the portable AC. Operating an air conditioner in tilted position can damage the compressor and reduce life.

So, either you have taken your portable AC out after a season, or it has been placed in the tilted position for some time it is not right to operate it right away.

Pro Tips

  • Keep the unit upright for 1 hour after it is taken out of the storage from tilted position. This will allow the oil in the unit to resettle before it is used.
  • After moving, give air conditioner about 30 minutes before operating it.

10. Air is Blocked at Intake

Portable ACs are designed for convenient mobility. However, movability of Portable AC is still limited as they operate on same principle as other air conditioners i.e., by the application of refrigeration cycle.

Air has to be taken in from the surroundings of portable air conditioner and delivered after it has absorbed heat from the condenser coil. Then warm air is rejected outside with the vent hose.

If you do not provide sufficient space around portable AC for intake, keep it covered or place something in front of it, air cannot be sucked in and prevent the refrigerant from cooling properly in condenser coils.

As a result, efficiency as well as the cooling effectiveness of the portable AC will be affected.

There are two kinds of portable ACs in the market: Single Hose and Dual Hose. You will face this problem in single hose portable AC.

Single hose portable AC has only one hose coming out of it. Air is sucked from the portable AC inside the room. Warm air is then delivered outside after extracting heat from the coils.

In dual hose portable AC, this is not a problem. Air is taken in from outdoors by using another hose. But you should still give a check inside intake hose for obstruction, dirt or solid objects.

11. Inadequate Vent Hose Length and Orientation

You can extend the hose length according to requirement as they are extendable. In general, hose that comes with most portable ACs are extendable from 5-7 feet.

Using exhaust hose of greater length than that is recommended will reduce cooling effectiveness and operational efficiency of your portable AC.

If you want to buy longer portable AC hose you must avoid the the ones with length greater than 12 feet. It is highly recommended that you use the same hose that comes with your portable AC.

The reason is its maximum compatibility with your portable AC. In fact, try to extend the hose as less as you can to get maximum cooling.

Pro Tips

  • In case you damage your portable AC hose, it is highly recommended that you get one of the same dimensions and length as original.
  • Prevent bending the hose too much, as this will create obstruction for the warm air to pass. Especially prevent the hose to be bent at 90 degrees. If warm air is blocked, heat energy will not be rejected, and it will result in ineffective cooling.

12. Compressor Is Not Running: Faulty Relay or Capacitor or Lugs

There are rare situations in which your compressor is damaged. Normally when the compressor stops working the relay or capacitor is blown.

After you have assured that it is not one of the common problems mentioned above and there is no refrigeration leak check relay and capacitor. Below are provided the two cases in both of them compressor is not working. However, in one case the relay was damaged while in other case the compressor lugs were blown due to surge.

Compressor Not Working Due To Damaged Relay (Fixed)
Compressor Not Working Due to Damaged Lugs

In case compressor is not running due to damaged capacitor in most of the cases you will see a bulged capacitor on top. It is highly uncertain that despite the bulged body capacitor it is not the problem. In case of relay or capacitor damaged they are easily replaceable.

The video below is for diagnosis and replacement of capacitor in central air conditioning however procedure is the same in portable AC. Just make sure that you buy the relay or capacitor of the same specification required for your model.

Compressor Not Working Due to Faulty Capacitor