Air Conditioner Blowing Warm Air: 10 Causes & Solutions

Is Your Air Conditioner Blowing Warm Air? If so, you’re probably wondering what could be causing hot air to blow from my air conditioner.

To be honest, I have experienced this issue with my AC units, and as an air conditioner specialist, I have repaired many units that blow hot air. And the same tips I am going to tell you here. 

In this blog post, we will discuss 10 common reasons why your air conditioner blowing warm air, and provide you with solutions to get your air conditioner blowing cool air. Read on to learn more!

Why Is My Air Conditioner Blowing Hot Air? 10 Causes

Here are 10 common reasons why your air conditioner blows hot air. It’s important to identify the cause before taking any troubleshooting steps, so let’s cover that first.

#1 Thermostat issues (Most Common Cause of Air Conditioner Blowing Warm Air)

If your air conditioner is blowing warm air, the first thing you should do is check the thermostat. If the thermostat is set incorrectly or is malfunctioning.

Your thermostat may be reading the wrong temperature and sending the wrong signal to the air conditioning unit, resulting in hot air blowing from the unit instead of cool air.

We repaired over 1,000 air conditioning units last year, and over 30% of air conditioners that blow warm air have problems with the thermostat itself. 

Your thermostat should not be set higher than your room temperature, it should always be lower. You should also check and ensure that your thermostat is wired properly and also look at the battery, if it’s dead, replace it.

According to, you should replace it every year to avoid any problems with the thermostat. And beyond that, it’s important to make sure the thermostat is positioned away from any direct sources of heat, such as sunlight or radiators.

#2 Low Refrigerant Level

As you may already know, refrigerant is responsible for taking heat away from the room, and if it’s low, the air conditioner will blow out warm air instead of cool air. 

This is one of the most common causes of hot air from the air conditioner. You can check out these signs below to check for low refrigerant in your AC unit.

If you experience any of these symptoms, it may be that your unit has low refrigerant and needs to be refilled, and it is important to find out why your unit is getting low on refrigerant as well. 

One of the major reasons is leakage, inspect the unit and look for leaks, and if found, fix it as soon as possible. Learn: How to fix refrigerant leaks in ac units?

#3 Dirty Evaporator Coils

The evaporator coil is an important component of an air conditioner system. It is located inside your room. When air passes over it, it absorbs heat and cools the air. If the evaporator coils become dirty or clogged with dust and dirt, they are unable to absorb enough heat. This allows your air conditioner to blow hot air. 

To prevent the accumulation of dust and dirt on your air conditioner’s evaporator coils, it is important to clean them. This is a part of maintaining your air conditioner. 

And according to, dirty coils can increase energy use by more than 30%. This is a huge advantage. But how can you identify that your air conditioner coil is dirty, here are some signs by which you can identify a dirty coil:

  • Decreased cooling efficiency
  • Increased energy bills
  • Strange odors
  • Frozen coils
  • Loud operation of the AC

Cleaning the coils can be a daunting task if you have no experience, so it would be best to have an experienced person to help, by the way, if you are sure you can do it yourself by watching tutorials or reading how-tos then you can do it too.

Here are links to some great tutorials on cleaning evaporator coils:

#4 Clogged Condensate Line


A clogged condensate line often referred to as a drain line or drain pipe, is another common cause of hot air coming out of an air conditioner.

The drain line is the tube that drains the condensation away from the unit. If it gets blocked, water accumulates and can cause a variety of problems. 

These include water leaks, freezing in the evaporator coils, air not cooling properly before entering the home, and musty smell coming from the unit. 

To check for condensate lines, first, turn off the power to the unit. Then look for any evidence of standing water around the unit or any signs of overflow. 

If you see any of these, you’ll need to clean the drain line with a vacuum or other tools. It’s easy to do, and it won’t take long. So calling an HVAC technician for assistance will be a waste of money.

According to a 2019 survey by, 56% of HVAC technicians have seen clogged condensate lines due to air conditioners not blowing cool air.

#5 Fan Issues

A faulty or damaged fan motor can cause the air conditioner to blow hot air as the job of a fan is to move cool air throughout your home.

If your fan motor is not running properly, it will not be able to circulate cool air efficiently and effectively, resulting in hot air being forced out.

Apart from this, if the fan blades are bent or clogged, this can also reduce airflow and allow hot air to blow from the unit. And your air conditioner can make strange noises too. 

And as might be guessed, to avoid the issues you will need to inspect the fan and motor on a regular basis for any signs of damage and fix if anything is wrong, and to get the most mileage, make sure that the fan blades are not bent and free from dust and dirt.

According to, every year the fan motor should be inspected and replaced if necessary.

#6 Blocked Air Filter

A blocked air filter prevents airflow from fully circulating through your unit, causing your air conditioner to work much harder and longer. 

This can result in hot air coming out instead of cool air, plus the energy bill will shoot up to the roof. To prevent this from happening, you should check and clean your air filter regularly.


The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends cleaning or changing disposable filters every 30 days.

Cleaning your filter is super simple—just remove it from the system, vacuum any dust or debris off of it, and then place the filter back in the system, and you are good to go.

But the filter doesn’t need to be cleaned all the time, it also needs to be replaced and as a general rule, you should replace it every 3 to 4 months. 

Keeping the air filter clean at all times is a win-win situation. According to, an air conditioner with a clogged air filter can waste 5 to 15% of its energy output, so you can save 15% energy just by cleaning it.

#7 Malfunctioning compressor

The compressor is like the heart of your AC unit, if it is removed or damaged, yours AC will be out of business.

It is the main component of an air conditioning system, responsible for compressing and moving the refrigerant throughout the system.

If the compressor is faulty or not working properly, it will cause your AC to not cool down, resulting in hot air coming out of the vents.

According to the U.S. Department of Energy, a malfunctioning compressor can account for 30% of all air conditioning repairs. In order to determine if your compressor is bad, check for the signs below:

  • Noisiness
  • Overheating
  • Refrigerant leaks
  • Unit is not turning on
  • Tripped circuit breaker

You can also call a HVAC professional for help, it is recommended. If you find that the compressor is failing, it will need to be replaced in order to get your AC up and running properly again. 

#8 Incorrectly Sized Unit

For more than half the people who are buying AC units for the first time, the most common mistake they make is that they choose the wrong size unit to save money. Having a unit that is not suitable for the size of the room can cause your unit to blow hot air. 

For example, let’s say your room size is 700 square feet and you install a 6,000 BTU unit that is ideal for cooling a 250 square foot space, this will stress your unit, and will force it to work hard resulting in your unit blowing hot air.

Also, selecting a unit that is larger than the size of your room is also a no-no, as it will cool your room at lightning speed, but it will also result in frequent turning on and off of your unit, inadequate humidity control and causes a lot.

Here is a table of what size AC unit you need as per the size of your room.

Square FeetBTU’s
100-150 5,000

#9 Blocked Vents

Imagine what would happen if your air conditioner vents get clogged. Then your unit air has nowhere to go. This can cause pressure to build up in your HVAC system, forcing hot air through your registers.

To prevent it, make sure all your vents are open and unobstructed. You may need to move furniture away from vents or open curtains that are blocking them. If you have pets or small children, be sure they don’t accidentally knock any vents over.

Did you know? Blocked vents can reduce the energy efficiency of your air conditioning system by up to 20%.

#10 Dirty Condenser Coils

Dirty or clogged condenser coils can cause an air conditioner to blow hot air. It is responsible for removing heat from the air in your room before recirculating it back outside the room.

Over time, the coils can become clogged with dirt, dust and debris, causing the air conditioner to not operate properly. 

Condenser coils are easy to clean but can be tough if you are a beginner, but to help you do so, we have recently published a step-by-step guide about it which you can check out.

3 Tips to Prevent Your Air Conditioner from Blowing Warm Air

Now that you know why your air conditioner was blowing hot air, and you’ve resolved the issues, but what about the future, how can you prevent your air conditioner from blowing warm air in the future?

Well, here we will provide you 3 super actionable and easy tips to prevent warm air from the air conditioner. Keep reading.

1. Keep the air filter, unit and the area around your unit clean

If you want your AC to run properly and to keep blowing cold air, be sure to keep your AC unit, the filter, and the surrounding area as clean as possible.

A dirty filter will result in an AC running inefficiently and possibly blowing out warm air. To avoid it, clean the air filter every month. 

It is also extremely beneficial to keep the area around your unit free of debris such as leaves, grass clippings and sticks, as these can block air flow and prevent your unit from operating properly.

Apart from these, also keep in mind to clean the exterior of your air conditioner with a damp cloth every few months. This will help remove any dust or dirt that may have accumulated over time.

2. Inspect the unit yourself every 3 months

As we already know, the benefits of cleaning the air conditioner regularly, but it will be two times more beneficial if you inspect the unit yourself every 3 months. 

I know, it is recommended a technician is for inspection but here I am not talking about an annual tune-up, I am talking about 3 months inspection here. This inspections includes:

  • Check and cleaning the air filter, coils and the ducts
  • Checking and fixing leaks in the system
  • Checking and sealing leaks in the ductwork
  • Checking for low refrigerant and tefillin it needed
  • Checking and unclogging blocked vents
  • Checking and tightening electrical connections and loose bolts
  • Checking and fixing issues with the compressor, the fan and the motor.

Believe me, if you do this you will see an increase in energy efficiency, air quality and comfort, plus the chance of lasting your ac unit longer will skyrocket.

3. Give it an annual tune-up

It is also very important to give your unit an annual tune-up, and this should only be done by a professional HVAC technician because a professional technician is a professional and has more knowledge about tune-up than you. 

You will inspect your air tens of times but not find issues but once a professional will inspect they will find a lot of issues. An annual tune-up tasks such as:

  • Checking the air filter
  • Checking refrigerant levels
  • Testing electrical connections
  • Cleaning the condenser and evaporator coils
  • Cleaning the blower and fan
  • Inspecting the thermostat
  • Checking the ductwork
  • Verifying proper operation
  • Checking the compressor
  • Lubricating the moving parts
  • Checking the refrigerant lines
  • Testing the safety controls
  • Checking the condensate drain
  • Examining the insulation

Learn more: What Is An AC Tune-Up and Is It Worth It?

FAQ: Why is my air conditioner blowing warm air?

Here I will answer some of the most commonly asked questions about hot air coming from a unit, that people most likely to ask in online communities and in-person with our staff when they go in for a repair.

Q1. Can a bad compressor cause an air conditioner to blow warm air?

Ans: Yes, a bad compressor can cause an air conditioner to blow warm air. Since a bad compressor will not be able to circulate the refrigerant properly, this can result in hot air coming from the aircon.

Q2. How often should I perform a tune-up on my air conditioner?

Ans: Once a year, you should perform an annual tune-up on your air conditioner, but not yourself with the help of a professional technician.

Q3. Can regular maintenance prevent my air conditioner from blowing warm air?

Ans: Yes, regular maintenance keeps your air conditioner from blowing hot air, but only if you do it properly and with the right tools and equipment.

Q4. Can an air conditioner blowing warm air result in higher energy bills?

Ans: Yes, of course, air conditioners blowing warm air can result in higher energy bills. Because an AC unit that is not working properly has to work harder and run longer to cool your home, which can increase your energy consumption and result in higher utility bills.

My final thoughts on Air Conditioner Blowing Warm Air

An air conditioner not blowing warm air can be caused by a number of problems, some of the most common being thermostat issues, low refrigerant levels, and dirty coils.

It’s important to identify the problem because there’s no mean of having an AC unit if your unit is blowing hot air. Regular maintenance and tune-ups can help prevent these types of issues in the future and extend the lifespan of your AC unit.

We have a complete guide to air conditioner maintenance, check it out.

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David Jack

David Jack

David Jack is a veteran when it comes to air conditioners, he love helping people find solutions to their problems with AC units. His specialty is helping people find the right Air-Conditioner for their needs, whether that means replacing a broken unit or adding on to an existing system. He is also great at diagnosing problems and fixing them quickly. He learned this from my father Jack Smith who was an air conditioner repairer, he has 2 years of experience in this field.

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