Why Is My Air Conditioner Blowing Hot Air? 11 Possible Causes and How to Fix Them

When your AC is blowing hot air on a scorching summer day, you’re going to want to find the cause of the problem—and fast. Not only will the hot air blowing inside the house make you break a sweat, but it could also mean there’s a serious problem with your cooling system. The faster you find the issue, the faster a pro can come in and make repairs, saving you from even more expensive repairs and cooling off your home in no time.

1. Incorrect Thermostat Settings 

It’s easy to set a thermostat to an incorrect setting, especially if you have a busy household. Before heating up at the thought of a broken AC, take some time to investigate the thermostat, which tells your AC to cool your home. 

How to Fix It 

When looking at your thermostat, ensure it’s on cool mode, not heat mode. 

There are many ways to accidentally bump a thermostat or change settings—children playing, a bump with a purse or backpack, or an accidental tap on a smart thermostat app. It’s also easy to forget to change the thermostat setting from heat to cool when the seasons change. If you’re nearing the first days of winter, be sure to check the setting. 

If your thermostat is on the cool setting, but your AC is still not blowing cold air, check the thermostat to ensure the fan setting is on auto. When it’s set to on, your air conditioner’s fan will blow air continually, even if it’s not cooling your house—meaning it will circulate warm air when your AC is not pumping cool air.

2. Dirty or Clogged Air Filters

A dirty or clogged air filter is a common reason your AC is not cooling properly. The air filter traps dirt, dust, and other foreign particles and prevents them from circulating in your home. This is great news for your air quality, but all of that yuck has to go somewhere. 

A dirty filter prevents free-flowing air from moving through your AC system. When the air cannot move freely, your AC has to work harder to cool down your home, making it feel warmer in the process. Remember that an air conditioner working double time will eventually break, which can be expensive to replace or repair. 

How to Fix It 

The air filter should be changed monthly, depending on several factors for your home. Things like the number of pets you have, the number of smokers in your household, and the square footage of your home all play an essential part in how soon you need to replace the filter. Changing your air filter before it gets too clogged will help keep your unit running smoothly. 

3. Dirty Evaporator Coils

The evaporator coils in an AC are often overlooked, but they’re an essential piece of the equation when keeping your home cool. Evaporator coils absorb the heat from your home. When dirty, these do not function properly and cannot work to help bring the temperature down. 

How to Fix It 

This common problem is easily fixed with routine air conditioner maintenance from an HVAC pro. You can clean your air conditioner coils yourself in just a few steps if you’d like to help maintain the life span and efficiency of your AC. 

4. Frozen Evaporator Coils

Evaporator coils are an important part of the AC system, as they hold refrigerant and allow it to cool incoming air that will then be dispersed throughout the home. But evaporator coils can freeze, often when airflow is limited. Airflow can be disrupted by dirty air filters, drain line clogs, or closed vents. Low refrigerant or a coolant leak can also cause evaporator coils to freeze.

It seems counterintuitive at first that frozen coils would lead to hot air, but if the coils are frozen, they aren’t able to turn the refrigerant from liquid to gas and back to liquid again. Why does this matter? This process is what cools the air for your home.

How to Fix It

It may be tempting to bring out a few tools and start digging out the ice, but you could accidentally puncture parts of the AC system if you try that. Instead, turn off the AC and hire a pro to take a look. If there’s a refrigerant leak, you’ll want a pro to find and fix it as soon as possible.

5. Your Outdoor Unit Lost Power

Air conditioners are multi-unit systems. The indoor unit blows the air around and through your home, while the outdoor unit is the actual structure that cools the air down. If you notice that your AC is blowing warm air, it could be because the outdoor unit has lost power and can’t cool down the air. 

How to Fix It 

Generally, this is due to a blown fuse or a tripped circuit breaker. You can check your circuit breaker box; if the breaker is flipped off, you can simply flip the breaker back into the on position. This should restore the outdoor unit's power to cool the air again. 

If the breaker in the box isn’t tripped, but the unit still doesn’t have power, a blown fuse might be the culprit. To ensure this problem is being corrected safely (and to diagnose why it’s blown in the first place), contact an HVAC professional to scope out the problem. 

6. Clogged Condensate Drain Line

Your AC is responsible for cooling your home and pulling the humidity out. The drain line moves water from the drain pan to the outside of the unit. If there is a clogged drain line, the water cannot flow freely and can cause several issues, from mold and mildew to the complete failure of your air conditioner. 

Besides your AC blowing warm air, other signs of a clogged condensate drain line include:

• A puddle of water near your indoor unit

• A moldy smell coming from your air vents

• Condensation on the AC unit

• Water damage near your indoor unit

• Your AC not starting

How to Fix It 

Drain lines should be cleaned every three months to ensure no clogs are forming. The great news is that you can clean an AC drain line yourself. Tackling this quick project can help keep your AC blowing cool air. Still, if the clog is too big to handle or repeated cleaning doesn’t help, a local air conditioning professional can help diagnose a more severe problem.

7. Refrigerant Leak 

Your AC's refrigerant is what keeps things cool. This liquid is responsible, in part, for absorbing heat and humidity in your home. If you have the correct thermostat setting and your coils are clean—but you’re still not getting cold air—your refrigerant levels might be low due to a leak. This leak will cause your AC to blow warm air, as it must work hard to reach the set temperature. 

It’s important to note that an AC refrigerant leak is not fatal but can cause health problems if left untreated. Some typical symptoms of refrigerant poisoning can include coughing, respiratory distress, dizziness, and headaches. 

How to Fix It 

If you suspect a refrigerant leak, turn off your AC unit and unplug the power source, if applicable. Fixing an AC refrigerant leak is best left to the pros, even if you can see a visible hole in one of the coils. An HVAC technician will assess the cause of the leak, often using special equipment. They can patch the cracked coil if the hole isn’t too big or replace the whole coil if it is too damaged. 

Hiring an HVAC tech can help find a problem that’s not related to a coil; these could include:

• A clogged air filter

• A cracked drain pan

• A clogged drain line

While it might be tempting to try to diagnose and fix the problem yourself, most refrigerant leak repairs require the tools and skill sets an HVAC pro would have. Plus, due to the hazardous nature of the refrigerant itself, it’s best left to the pros to tackle.

8. Air Duct Leaks

If you’re getting hot air when you run your AC, your air ducts might be to blame. Your ductwork delivers cool air throughout your home when you run the AC. When there is a big enough leak, the warm air that leaks in can mix with the cool air being pumped into your house, resulting in hotter air. 

How to Fix It

An HVAC pro can ensure your ductwork is clean and sealed correctly. Whether you’re having any issues or not, you’ll want to have your ducts cleaned and serviced about every three years to ensure everything works correctly and prevent future problems.

9. Malfunctioning Condenser Fan

Your AC’s condenser fan moves heat from the refrigerant system to the outdoors, keeping things from overheating. An overheated air conditioner can lead to full-system failure and could be costly to replace. An AC fan not working could be due to the following: 

• Fan blades not turning due to electrical issues or a broken motor

• Fan operates slower than required due to issues with a circuit board

• An obstruction where the fan blades turn

• Warped fan blades due to usage over time 

How to Fix It 

Because the condenser fan could have various problems, it’s best to leave the diagnosis and repair to a licensed HVAC technician. They will check the fan, blades, and all to ensure all parts are working properly. During routine air conditioning maintenance, your tech will inspect the condenser fan for proper upkeep. 

10. Damaged Compressor 

Your air conditioner’s compressor is the system that moves the refrigerant through the AC unit. If all of the above steps have checked out and aren’t seeming to be the problem, you might have a damaged compressor. If the compressor is damaged, it cannot move the refrigerant, meaning it cannot cool the air.

How to Fix It 

Fixing a damaged compressor can be expensive and does require a licensed technician to diagnose the issue correctly. The cost of an AC compressor can range between $800 to $2,800. Depending on the age of the compressor, it might be worth it to replace the whole air conditioner. 

Both air conditioners and their compressors last up to 15 years. If you're putting a new costly compressor into an old unit, you might find yourself replacing more parts down the road. 

11. Return Vents Blocked or Closed

Maybe a family member accidentally shut a return vent, or kids have piled up their toys in front of the vent. However, return vents need to be open and clear to keep a balanced air pressure in the ductwork. If you close a return vent in the hopes of redirecting the air, or if the vents get blocked by furniture, toys, or other household objects, air pressure can build up, causing air duct leaks.

Blocked or closed return vents also cause the system to work harder to push cooled air throughout the home, which will put more wear and tear on other parts of the system, like the fan and fan motor.

How to Fix It

Fortunately, you can fix a blocked or closed return vent without any special tools or expertise. All you need to do is check the return vent locations around your home for any obstructions. Then, move anything that may be blocking the vents. If the vents aren’t blocked, make sure they’re open. To open them, use the louver on the side of each vent.

Know When to Replace an Air Conditioner 

Sometimes, there is not one specific problem with your air conditioner; it could be too old to continue doing the job it once did. As stated above, air conditioners last between 15 and 20 years. There are times when the cost of buying an air conditioner is more cost-efficient than the HVAC repair prices you’ll need to pay to keep an older unit running. 

Of course, the best way to avoid replacing your air conditioner sooner than 15 years is to have your AC serviced at least once a year by a licensed HVAC technician to make sure it’s in tip-top shape to cool your home.