15 reasons the AC is running but not cooling (and how to fix it)

It’s summertime and time to revive units back to life. However, it’s when most homeowners realize their AC isn’t cooling as much as before. You’ll learn how to fix it. There can be several reasons for this, but we’re going to help. You need not break into a sweat, literally! Here are the top 15 reasons why the AC is running but not cooling your home as efficiently.

Cute girl next to a portable air conditioner

Why is my air conditioner running but not cooling the house?

Most common reasons 
Filter needs cleaningSunny spotThermostat settings
Improper placementRefrigerant needs refillingRefrigerant Leaking
Dirty outside unitA problem with the DuctsTripped circuit breaker
A faulty motorToo much ventilationSensor problems
Fan problemsClutter near the outside unitA fuse is blown

Let’s run through the most common problems of a non-functioning air conditioner.

  1. The filter needs cleaning.

Now here’s an important but very common problem. Here’s a likely scenario. It’s the first hot day after spring, and you’ve turned your AC on for the first time after a couple of months. It is only blowing wafts of hot air. Most likely, the filter is dirty from bits of dust accumulating over the winter. The clogged dirt is blocking proper airflow.

Luckily this is a problem you can repair at home within an hour. Turn it off, and remove the filter. Now remove the top attachment of your vacuum and run it over the filter to remove the dust. Head over to the bathtub and use a mild soap solution to wash your filter and scrub gently. Rinse and leave to dry. Reinstall once the filter is dried completely. You should notice the airflow is better and cooler.

If you want to skip this process entirely, you can go for disposable filters to save on time.

air duct
  1. Sunny spot

A window AC installation may seem easy but prove inefficient if the window is in a sunny spot. Direct sunlight can make it harder to cool your home in the long run. There is space around your window model that is letting hot air in or cold air out, making it difficult to bring down the inside temperature.

You can try finding a window in the shade and move your unit to fix this. If this isn’t possible, a simple curtain or shade can temporarily avoid overheating the unit.

  1. Thermostat settings

If you find yours is running but not lowering the temperature, the first thing to do is check the thermostat settings. Sometimes the mode might be incorrectly set to ‘Heat’ and not ‘cool.’

Get your remote control or touch panel on the AC checked if you cannot change the mode.

  1. Improper placement

You may be wondering why it isn’t cold despite installing a split model. This might be simply due to the improper placement of the unit in line with direct sunlight, as mentioned above. The other reason could be that it is only powerful enough to cool a medium-sized room. It would have to work twice as hard and take much longer to cool a large hall or living room. The heat will get in with frequent doors opening in such a room. Therefore, the room might not get cold as efficiently.

air conditioners outside

Consider getting a more powerful model for a larger room. If the room is between 200-300 square feet, consider getting a 1.25-1.5 Ton AC. For rooms even larger, you must go for at least 1.5 tons.

  1. Refrigerant needs refilling

Refrigerant is the liquid enabling the cooling aspect of the unit. Sometimes this will need refilling, and you will need to call a professional or learn how to refill it yourself. If you find that the refrigerant is low due to leakage in the pipes, you’ll need to fix the holes. Read the next point on how to deal with this.

  1. Refrigerant Leaking

This is common to old ‘units since the metal pipes can corrode over time from formaldehyde or formic acid. This will mean seeking professional help to replace the individual coils or the entire coil system. In some cases, experts resort to welding the individual leakage points. Check out these welding helmets if you’re looking to do this yourself.

Only after fixing all the holes in the coils should refrigerant be added again. Refrigerant leakage can cause environmental damage and thus should be monitored periodically.

  1. Dirty outside unit

You’ll find an outdoor counterpart in both split and window models. This outer part contains a condenser that turns the hot air into the cold. Since it is placed outside, it is prone to dust and weeds. You could also have issues with debris. You’ll need to get your cleaning tools out and work on cleaning the outside unit and its immediate surroundings. This can also be done with an expert’s help. If you’re looking for an outside electric socket, you might want to check out these extension cords by length.

  1. A problem with the Ducts

Ducts will need proper and timely maintenance in a central air conditioning model since ducts distribute the cold air throughout your home. Noise in the ducts will alert you of any leaky ducts or obstruction in their working. Pests or incorrect installation can also cause obstructions in the ducts. Seek expert help or learn how to clean the ducts yourself.

air conditioning units

Maybe you live in a neighborhood with frequent power outages but want a cool home all day long. You can check out the best watt generators.

  1. Tripped circuit breaker

If your air conditioner is not turning, it may be due to the tripped circuit breaker. It could be due to overload on the electric circuit. Reset the circuit breaker and consider getting an expert to check the total load on the circuit. Consider reducing the number of appliances on the circuit. Or you can learn more about single-phase and three-phase power.

  1. A faulty motor

If you find it stopped working, a faulty motor in the external component might be a possible cause. The motor functions to convert the hot air into cold air. If the air is blowing hot through your ac, it might be time to check the motor.

A faulty motor will need repairing or complete replacement with a new one. Check out these amp wire resources if you’re doing the repair work yourself or reinstalling a new one.

  1. Too much ventilation

Evaporators take the existing humid air and convert it to cold air, and circulate it in the room. However, suppose the room is filled with windows and doors that aren’t properly shut. The sticky stuff will continuously seep in and hamper the cooling process. It will be almost impossible to reach the desired room temperature if this problem is not addressed. It doesn’t matter how powerful your model is.

Portable air conditioner

If it isn’t possible to completely shut off outside air, consider curtains or drapes. Shades are also a great way to limit the outside air and sunlight exposure.

  1. Sensor problems

The sensor located behind the touch panel measures the temperature of the air going in. If the sensor malfunctions, the room temperature could be assessed incorrectly. This might cause the cooling to be off. Keep in mind the sensor should never touch the coils and other components. Consider checking its placement for any signs of damage or dislocation.

Here is a list of sensors in the AC system.

Air temperature sensor
Discharge side sensor
Humidity and temperature sensor
Clip-on temperature sensor on suction line
A clip-on sensor on the return bend
  1. Fan problems

If you find the AC is not cooling, you find that the fan isn’t working upon checking the outside. Press the reset or overload button. If the fan still doesn’t work upon resetting, turn the fan clockwise. If the fan blades have no turning issues, the capacitor needs to change. If the blades don’t move or move with resistance and noise, it’s the fan that needs replacing. Research good fan options for your unit or seek professional help.

Here is a list of the fans in a normal AC unit.

  • One in the indoor unit which is used to circulate the cool air inside the room
  • One on the outdoor unit which throws the hot air outside
Man repairing AC units
  1. Clutter

The outer part needs sufficient air to dehumidify and send through the indoor unit. The outdoor part needs to remain clutter-free and have no overhead structures or any objects or plants 4-5 feet below. Check out this conversion chart if you’re still confused between feet and meters.

The outdoor unit will not be placed in a storeroom or adjoining wall of an inside room. It can only be placed on the airy outdoors on an apartment balcony or porch.

Maybe it is not placed in any of these places indoors. Consider relocation and reinstallation for better functioning capacity and cooling. Consider this wood chipper resource if you want to trim the trees around the outside unit.

floor register
  1. A fuse is blown

Maybe you feel you’ve tried all aspects of troubleshooting and still can’t find the problem. It might be time to check your indoor and outdoor unit for any signs of a fuse that has been blown. If it isn’t turning on, check the electric panel and call a professional electrician to fix the problem.

Let’s examine all the ways you can avoid such problems in the future. You’ve now learned the several reasons and their solutions to fixing the cooling of your air.

To sum it up

  • Improper placement
  • Refrigerant needs refilling
  • Refrigerant leaking
  • A fuse is blown
  • Clutter in the system
  • Fan issues
  • Sensor issues
  • Too much ventilation
  • A faulty motor
  • CIrcuit breaker tripped
  • Duct issues
  • Dirty outside unit
  • Thermostat settings
  • Filter needs cleaning
  • Sunny spot placement
rooftop air conditioning units

Tips for maintaining it at home

Here’s what you can do at home to maintain the longevity of your air conditioner.

  • Clean the filter
  • Clean the drain system
  • Prepare it for the winter
  • Professional maintenance
  • CLean the evaporator
  • Comb the coil fins

How to maintain your AC unit so it cools when it’s running

  1. Clean the filter every month.

    Cleaning a clogged and dirty filter can lower your energy consumption by anywhere between 5-15% in a central air conditioning unit. You can find the filter located in the return ducts. Suppose you wish to do away with the hassle of cleaning the filter every month during the summer season. In that case, it’s best to switch to disposable filters.

  2. Clean the evaporator and condenser coils.

    Dirt enveloping the evaporator will reduce its ability to absorb heat. It’s essential to dust them off with a dry cloth once in two months in the summer season. The outdoor condenser is more prone to debris and dust. It sits outdoors with possible leaves and gusty winds. The outdoor coil must also be checked and cleaned with a dry cloth once in two months in the summer.

  3. Check the condensate drain system.

    Take a stiff wire to pass through the drain pipe occasionally to check for any signs of clogging. If the water isn’t draining properly, this can damage your unit or possibly leak from the outdoor part and stain nearby items.

  4. Comb coil fins.

    There are aluminum fins on the condenser and evaporator that can bend over time. This causes a reduction in airflow and thus slower cooling. To tackle this, you can buy a “fin comb.” It will bring the fins back to shape.

  5. Prepare it for winter.

    You must pack up your air conditioner unit when it’s no longer going to be in use for several months to come. Purchase a cover and use it to shield the condenser from dirt and debris. You can also remove it, pack and store it in your home. Ensure the storage space you choose is cool and dry, free of moisture and any pests.

  6. Regular professional maintenance.

    You can also hire a professional to check and service it at the beginning and end of the summer season. Make sure it’s working at its best. The professional will clean all the parts and check refrigerant levels and signs of leakage or broken fans. This may cost you some extra money but consider it an important investment in preserving it in the long run. Save all the money instead of buying a new one!

picture of an air conditioner

That’s all, folks! Keep up the maintenance to avoid any problems with your unit. Go through our 15 reasons to spot the problem you’re facing if AC isn’t cooling.


How do I fix my air conditioner that is not cooling?

One of the most common problems involves an unclean filter. You can clean this out. Also, check for electrical wiring issues. With a non-cooling air conditioner, the likely issue is refrigerant gas leakage. Get the holes welded, and you’re good to go.

Should I turn off AC if it’s not cooling?

Yes, certainly. It is most important in the repair process. This will anyway be required for the repair work to be done.

How long should it take AC to lower the temperature?

If your AC is the correct size for your home, it should only take around 15-20 minutes to cool the house. It could take longer if other issues like a clogged coil or filter or a possible leakage.

How do I fix my air conditioner that is not cooling?

There could be many factors for why the ac may not be cooling. Let’s look at them below.

1. Check your filter.
If your filter is dirty, it could block the cool air from distributing throughout the house. Take it out and clean it thoroughly using a soft detergent and small bristle brush. Rinse well and dry before installing again.

2. Check for leakages.
If the refrigerant gas leaks, it could cause a possible cooling issue. This would need welding and a gas refill to resume the cooling.

3. Check for duct malfunctions.
It could be that cool air can’t reach the surroundings because the duct is broken. If this is the issue, replace the duct or glue it using super glue to fix the problem.