Seven Common Problems In Your Home’s AC System That Would Cause It To Blow Warm Air (With Solutions)

Kenneth Wilson

Few things in life are as frustrating as your AC blowing warm air. When temperatures soar in the summer months, we turn to our home AC to keep us cool and are incredibly frustrated when we feel warm air gushing through the vents.

So, what causes home AC systems to blow warm air?

Frankly, there are many potential reasons why your AC might be blowing warm air, and many of them tend to be linked to a poorly maintained system.

To help you fix your home AC and prevent it from blowing warm air in the summer months, we introduce seven of the most common problems with home AC systems and emphasize just how important it is to keep your AC regularly maintained.

Maintaining Home AC Regularly

84% of homes in the United States have some type of air conditioning, and it's more common for US homes to have an AC unit than a dishwasher, dining room, or garage.

But despite this, less than half of US homeowners hire a professional to maintain their AC units regularly. AC units that are periodically maintained last on average 40% longer than those that aren't, and common issues tend to be diagnosed and solved before they become a significant issue.

If your AC is blowing warm air, it may be down to various factors, as we introduce in the following section. But one of the most glaring problems with AC units in the US is that they aren't often maintained by homeowners, as exemplified by the above statistics.

Experts recommend calling in professionals to maintain your AC at least once a year, as this will help keep your system fully functional and free from a range of issues. (Related: 9 Things To Know About The Air Conditioning System In A Florida Home And #9 May Be The Most Important!)

That being said, there are lots of potential reasons why your AC is blowing warm air, and you don't necessarily need to call in an expert to resolve the situation, as we introduce below.

Why is my AC Blowing Warm Air? Seven Potential Problems and Solutions

As you look for an escape from the burning heat outside, you're understandably excited about experiencing a draft of refreshing, cool air from your AC. But it never comes. Instead, you're treated to even more warm air, which makes you even more uncomfortable than you already are!

While this is incredibly frustrating, an AC blowing warm air is a fairly common occurrence for homeowners across the United States, so you're certainly not alone!

To help you diagnose and fix the problem, we introduce seven of the most common potential reasons why your AC is blowing warm air, with an explanation of how to hopefully fix your system and enjoy the cool breeze that you so desire!

1. Thermostat Issues

You'd be surprised at how often a thermostat gets tampered with. If you live in a busy home, you might find that someone has either unintentionally (or deliberately!) altered the thermostat settings, causing your AC to blow warm air instead of cold.

Perhaps your kids knocked it as they ran past, or maybe your elderly mother got tired of the relentless cold air circulating around her bedroom and forgot to change the setting back as the temperature increased. Either way, if your AC is blowing warm air, your first port of call should always be the thermostat.

  • Solution: Check the thermostat. Although every AC system works slightly differently, make sure the thermostat is set to 'COOL' and the fan is on 'AUTO.' You will also need to check that the temperature is lower than the air temperature. If the thermostat has been tampered with, a quick check and reprogramming will be enough to stop your AC from blowing warm air.

2. Clogged or Dirty Filter

If the airflow within your AC is reduced or impeded, it can restrict the cooling operation of the entire system. And the most common cause of reduced airflow within an AC is a clogged or dirty filter.

An AC system works by allowing warm air to pass over the coils, and the filter is there to remove dust, debris, and other air contaminants from the system. If your filter isn't regularly cleaned and maintained, it can easily become clogged, preventing air from flowing through the system and recirculating as cold air.

Instead, your AC's fan merely blows heat back into your home, as it is unable to pass through the dirty and clogged filter.

  • Solution: Clean or replace the filter. If you suspect that your AC is blowing warm air because of a dirty or clogged filter, the good news is that you can easily clean or replace the filter yourself. First, turn off your AC system and slide the filter from its slot. At this stage, hold the filter up to a light and inspect its condition.Should the filter be covered in dust and particles, you can vacuum each side and return it to the AC unit. If this doesn't seem to do the trick, your system's filters might have to be replaced. Remember that all sorts of environmental factors (such as pollution) can affect the quality of an AC's filter, so replacing the filter once in a while is certainly not a bad thing.

3. Blocked or Closed Return Vents

Because you can't feel air coming out of return vents, people often mistakenly think that it's okay to close or block them without affecting the system. Like filters, return vents also accumulate a lot of dust, dirt, and other air contaminants and should be regularly checked and cleaned.

If the return vents are closed or blocked by clothes or furniture (which is common in homes), the AC system can't function properly, and it can cause your AC to blow warm air instead of cold.

  • Solution: Check the return vents. The good news is that it's super easy to check if the return vents are closed or blocked. Simply go to the location of the vents and check that air is able to pass freely through the vents. If they're closed, open them, and if they're blocked, clear the obstruction.

4. Frozen Evaporator Coils

Evaporator coils are one of the most integral aspects of an air conditioning system. Their job is to extract heat from the air in your home to begin the cooling process. But an unavoidable by-product of this process is condensation, which tends to be collected in the system's drip pan.

However, in some instances, the condensation can freeze to the coils, preventing the heat transfer process. Instead of blowing out cold air, your AC will blow warm air as the evaporator coils cannot do their job correctly.

  • Solution: Thaw the coils. If the evaporator coils within your AC system have frozen, you will need to thaw them for your system to function as expected. After turning your AC off, you will then need to open the access door to the interior system to check the coils.A quick glance will be enough to see if the coils are frozen or covered in frost. If this is the case, you should allow them to thaw for at least 24 hours before turning the system back on again.You will need to check whether the coils freeze again in the coming days, as it's often a sign of a deeper root issue with your AC. Coils freeze and cause your AC to blow warm air due to poor airflow, refrigerant leaks, and other problems that may be difficult for you to identify. You should call a professional maintenance team if you’re unable to find the problem yourself.

5. Leaky Ducts

Another potential reason why your AC is blowing warm air is a result of leaky ducts. Leaky ducts can be caused by adverse weather, rodents, other pests, and general wear and tear on the system. Small holes or cracks in your ducts will affect the ability of your AC to circulate cold air.

You might even find that a duct has been completely disconnected without your knowledge, which means return air is unable to make it back to your AC unit.

  • Solution: Check your ducts for damage. As mentioned, leaky ducts may have been caused by a range of factors outside of your control. But the damage may also have resulted from recent construction work that has occurred at your home.Whatever the cause, if your ducts are positioned somewhere that you can inspect them yourself, take a look at their exterior and check for any holes, tears, or rips in the surface.If you're able to identify damage in your AC's ducts, you will need to contact a professional HVAC team to replace them.

6. Electricity Disruption

For homeowners who operate a split AC system with indoor and outdoor components, both aspects of the system must be working in order to deliver cool air to the interior of the property. If there's a loss of power to the outside unit, the system will not be able to cool sufficiently, and therefore your internal AC will blow warm air.

While a general power outage may have caused the electricity disruption, it can also result from a blown fuse or your outdoor unit tripping the circuit breaker.

  • Solution: Check the power supply of your outdoor system. Head outside and check that your outdoor AC system is currently supplied with power. At this point, you can also check whether the breaker has tripped and reset it if necessary. Finally, it's worth checking whether the emergency switch has been accidentally shut off, which can happen if your AC unit is located in a communal area.It's super important that you don't try and diagnose complex electrical issues with your AC unit yourself unless you're a qualified HVAC technician. If your outdoor AC unit has no power and you're unable to diagnose why, it's best to call in the help of a professional to stop your AC from blowing warm air.

7. Leaking Refrigerant

Refrigerant flows through your AC system and essentially makes the cooling happen. As you may be aware, you don't need to top up AC refrigerant, as it runs on a closed loop. But if your system has a leak and refrigerant escapes, your system can no longer create cool air, which means your AC blows warm air back into your home.

Leaking refrigerant often goes hand-in-hand with frozen coils and a hike in your electricity bills, so you may be able to diagnose the issue due to an accumulation of these factors.

  • Solution: Call a qualified HVAC technician. If your AC is blowing warm air because of leaking refrigerant, you will need to call a qualified HVAC technician to fix the issue for you. Not only will they need to fix the leak, but they will have to replace the refrigerant, and ensure the system is running smoothly.Leaking refrigerant tends to be an issue in older AC systems, but it can also occur in newer systems that are faulty or have been damaged. Whatever the cause, you should hire a professional to help you fix the problem.


Poorly maintained AC systems are much more likely to blow warm air than those that are regularly serviced. By checking your AC system every couple of months and cleaning the filters, you can ensure your AC system is constantly able to circulate clean, cold air into your home.

We also suggest hiring a qualified HVAC technician at least once every year, so they can diagnose any issues that may arise, and ensure your AC system is working when you need it the most!

The seven most common problems that cause an AC to blow warm air, as introduced above, can be largely avoided by taking care of your system and ensuring it's clean and well maintained, even when it's not in regular use.

Kenneth Wilson
September 1, 2021
Contractor Tips, HVAC

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

Ask The Author Your Questions In The Comments!

{"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

More From This Author