8 Reasons Your Air Conditioner is Blowing Warm Air (And How To Fix It)

What’s going on with your air conditioner? Why is your AC blowing warm air all of a sudden? Is it something that you can fix yourself, or do you need a pro?


Well, in this article, we’ll highlight the common causes of AC blowing warm air, and a few crucial tips to troubleshoot and fix the problem.

Let’s jump right in;

1. Dirty Air Filter

The air filter is an essential part of your AC unit. Therefore, if your AC is blowing warm air, it might be because your air filter is dirty.

When dust and other air pollutants are stashed on your unit’s air filter, they reduce the airflow. As a result, the hot air will flow out through the grates and ducts.

Solution: Simply replace it with the best AC filter for airflow.

If you have a reusable filter, all you need to do is clean it.

2. Thermostat on Heat Mode

This may sound quite obvious, but if your AC is blowing warm air, it might be because you accidentally activated the heating mode in the thermostat settings. Now, the fan is blowing warm air through your home.

Solution:  Check if the thermostat is set to “cool” put it on “auto” (not “on”) so that the air conditioner knows when to blow cool air.

It’s a good idea to set the thermostat at about 78 degrees Fahrenheit when you are at home and some 10 degrees higher when you are away.

Lastly,  if you’re using a wireless AC, you may want to confirm if the thermostat’s batteries are still functioning.

3. Dirty Evaporator Coils

In case your AC is blowing warm air, aside from cleaning the air filter, you might have to clean the evaporative coils. It’s good to clean your air conditioner regularly to prevent dirty and warm air from escaping.

Solution:  Hire an HVAC professional to clean the evaporator coils or tackle it yourself.

4. Frozen Evaporator Coils

Your air conditioner’s inability to maintain the thermostat setting might be due to frozen evaporator coils. A dirty air filter can often cause the airflow in your HVAC air conditioning system to be disturbed.

As a result, the coils can’t evaporate the condensation produced during the cooling process. Without that airflow, the condensed air will get so cold that it will most likely freeze. At this point, it can no longer absorb the heat, and the AC blows warm air as a result.

Solution: Turn your AC unit off first so that the coils can thaw.

In case of moderate frost,  you can set your thermostat to fan mode. This way, the fan will blow warm air throughout the coil without hindering the cooling function. The wave of warm air coming and going through the unit should speed the thawing process.

You can then clean the dirty air filter or replace it.

5. Wiring Issues

You may have cut, frayed or damaged wires in your indoor or outdoor unit unknowingly. In these circumstances, your air conditioning system might end up performing poorly and eventually break down.

Besides, pets or mice are fond of chewing the internal unit’s wiring once they gain entry.

Solution: If you don’t have any coating,  seal the wires with electrical tape. And since sealing is a short-term fix, you may want to find a professional to change the wires.

6. Damaged Compressor

Because the compressor is a crucial part of your air conditioner system, its malfunctioning can cause the condenser unit to stop working altogether. As already probably know, the compressor is the heart of the AC. It pressurizes the refrigerant to absorb heat from the air and release it outside.

Here are the five common culprits of AC compressor failure;

  • Dirty condenser coils
  • Refrigerant leaks
  • Blocked refrigerant lines
  • Electrical complications
  • Insufficient oil lubricant
  • Manufacturing issues

Solution: Refrigerant leaks are most likely to be the problem, so you might need to top it up.

IMPORTANT! Sadly, you cannot fix the compressor yourself. So, whether you have a refrigerant leak problem or an electrical problem, please contact a professional.

7. Lack of Electricity to the Outside Unit

If you have a split AC system, then the problem might be caused by the lack of electricity to the outside unit.

If its power is interrupted, the indoor parts may be the only working ones, which can cause warm air to go through your HVAC system.

Solution: Check to ensure the unit has power. Inspect the breaker, as well as the ON/OFF button of the unit.

8. Condenser Coils (Outdoor Unit)

Finally, if everything else fails and your air conditioner is still blowing hot air, you need to check the outdoor unit’s condenser coils. Just like the evaporator coils require a good airflow, so do the condenser ones.

Most of the time, this is caused by a clog.

Solution:  Shut down the system and clean it to remove the debris.

The Bottom Line

As you’ve seen, if your AC is blowing hot air, the problem may be anything from the refrigerant to the filter or an electrical wiring problem. Most of the time, you can prevent this with proper maintenance.

In case your air conditioner keeps on blowing hot air after several fixes, you can buy a budget AC to use in the meantime. Check out our portable AC under $200 guide. 



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Ronald Watford, the owner of Quality Home Air Care, is a qualified HVACR technician and manages the team of expert writers on this site. He believes that educating homeowners about HVAC systems is one of the most impactful aspects of his job.