Don’t sweat. In this guide, we’ll help you troubleshoot an AC system that’s blowing warm air.
It’s a tale as old as HVAC systems. A summer heat wave hits and all you want to do is to retreat into your home, where it’s nice and cool. Well, that’s a no-go if your AC is not blowing cold air.
An air conditioner blowing warm air is not just uncomfortable. It can lead to muggy rooms, poor air quality, and high humidity in the house, which carries its own issues.
Why is your AC blowing warm air? The culprit could be anything from your thermostat settings to a refrigerant leak. No matter the cause, we’ve got some fail-safe solutions.
By the end of this article, you’ll know how to get your AC back into shape—and bring your home back to the comfortable space you love.
Here’s what we’ll cover:
- Reasons your AC is not blowing cold air
- Where to start when your AC stops blowing cold air
- How to stop your AC from blowing warm air
- Why sealing and insulating your home can help keep your air conditioner working well
- Frequently asked questions about ACs that blow warm air
Reasons your AC is not blowing cold air
One thing’s for sure: If your heating and cooling system is acting up, there’s a good reason for it.
No matter the cause, it’s important not to wait until the heat gets too tough to bear—there is nothing like being trapped in a hot, stuffy house with no signs of relief.
So without further ado, let’s dig into the nine most common reasons for an AC blowing warm air (in no particular order).
Reason 1: Your thermostat settings are wrong
Sometimes the reason why your AC is not blowing cold air starts and stops at your thermostat. If this is the case, there are a few things to consider.
First, you may notice your system set to ON (fan mode). Believe it or not, the thermostat’s constant fan setting can cause your AC to blow warm air. Instead of fan mode, switch to your automated cool setting or AUTO.
The AUTO setting will turn off your unit automatically when the temperature gets too high. You can also switch to a manual mode and set the AC to the temperature of your choice. (Check out What’s so smart about smart thermostats? to learn how smart thermostats can help cut energy waste.)
Need to power up? Some thermostats require batteries to work properly, so make sure your thermostat’s good to go.
U.S. Energy Information Administration
Did you know? More than half of energy use in homes is for heating and air conditioning.
Reason 2: You have a refrigerant leak
Thermostat working just fine? Give your refrigerant a listen. And by listen, we mean keep your ears perked for a distinct hissing noise. This is one of two clear signs of a refrigerant leak. The other is frosted-over evaporator coils on your AC unit, but you won’t spot these if your AC is not blowing cold air.
Coolant is the VIP when it comes to your AC unit’s cool air. It moves through the system’s indoor and outdoor coils, pulling heat and humidity from the air inside and sending it out. Without enough of this chemical coolant, also known as freon, your AC can’t produce cold air.
Coolant doesn’t run out unless there’s a leak! Freon leaks can be toxic and make people sick, so if you think there might be a problem here, turn off your AC and get this fixed ASAP!
Reason 3: Your coils need to be cleaned
Most AC units have two sets of coils:
- Evaporator coils are where the cold air comes from. They’re located near the indoor blower unit and work by using refrigerant to absorb heat.
- Condenser coils are on the outside part of an AC unit. They’re made up of several parts that work together to turn the refrigerant into a gas by putting pressure on it.
Over time, both the evaporator and condenser coils can get dirty or grow mold. Both of these coils should be cleaned well at least once a year. Learn the steps for cleaning AC coils.
Reason 4. Your air filters need to be replaced
While we’re on the subject of dirty AC components, let’s get to know air filters.
Air filters have a pretty dirty job. They trap dirt, dust, and other airborne particles before they reach your home’s airflow. No wonder most experts recommend changing filters at least every 90 days.
Keep in mind, your air filters have a bit more work to do depending on:
- Your home size
- The number of pets in the home
- If anyone in the home smokes
- If people in your home have allergies
If you tick any of the boxes above, you may want to replace your air filters even more often.
Reason 5: Your compressor malfunctioned
Without a working AC compressor, the gas from the condenser coils can’t turn into liquid, and then cool the air, which means the refrigerant can’t do its job, and—well, you see where this is going.
The compressor is like the heart of your AC unit—it controls all the other parts of your air conditioner. Some other signs of a broken compressor are shaky, noisy units, and moisture around your AC system.
Reason 6: Your outdoor AC unit is clogged
Branches, leaves, and shrubs—oh my! Your outdoor AC unit weathers every storm or gust of wind so there’s a chance the elements have caused a bit of build-up.
While a few twigs are usually harmless, debris on or around outdoor AC units can overwork your system, which can cause it to overheat and not work properly.
Reason 7: You’ve got a duct leak
Air goes on an epic journey through a series of air ducts before finally reaching the rooms in your house.
Let’s just say sometimes air ducts get a little… detached. Over time air ducts can slightly separate from your air vents, which causes two main issues:
- Hot air mixed with cooled air can make the air from your vents warmer than normal.
- It gets more and more difficult to keep your home cool.
Learn more about why proper air sealing and insulation (including sealing up air leaks caused by aging ductwork) help bring total comfort to your home.
According to Energy Star, 20–40% of conditioned air that moves through ductwork is lost due to duct leaks. That’s a lot of waste.Energystar.gov
Reason 8: You’ve got a tripped circuit breaker
Imagine an AC fix as easy as flipping a switch. Well, if your AC stopped blowing cold air because of a tripped circuit breaker, you’re in luck.
AC units usually use two circuit breakers, one inside and one outside. If your outside breaker is tripped, your AC may seem to work just fine—only your AC unit will blow warm air instead of cool. No problem. All you need is a quick breaker reset and you’ll be good to go.
Reason 9: AC unit needs to be replaced
We’ve reached the biggest reason of them all: You’re due for an AC unit upgrade. Some types of AC units can last up to 20 years or more with regular maintenance and sufficient insulation and air sealing to keep the unit from being overworked.
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Where to start when your AC stops blowing cold air
When an AC unit stops blowing cold air, sometimes it’s tough to know where to look first. Here’s a quick troubleshooting guide to help you pinpoint the root of the problem.
- First: Always start with your thermostat. Nothing like checking your settings to find all you needed to do was turn it on.
- Second: Check your filters. Not only do air filters keep the air in your home fresh and clean, dirty filters play a big role in your cool air flow problem.
- Third: Use your senses. Notice any vibrating from your outdoor unit? Any shaky, noisy units, weird smells, or moisture around your AC system? These are all signs of a faulty AC.
Still unsure? You may need an HVAC professional.
Got questions about your AC options? Call us—our expert team is here to help.
(If your home is eligible, you can get an energy-efficient heat pump heating and cooling system to replace your aging AC at no upfront cost—installed by a vetted local contractor you can trust. Learn more.)
How to stop your AC from blowing warm air
So now that you’re done troubleshooting your AC unit’s warm air problem, it’s time to decide if you’ll outsource your repair or try some fail-safe DIY fixes on your own.
Air conditioner repairs can range anywhere from the lower hundreds to over $1000, and that’s not including the cost of AC unit replacements—if you end up needing one.
Then there’s the time and effort of finding a contractor you can trust. To save time and money, start by troubleshooting yourself. (Remember: Keep safety in mind and refer to your AC’s user manual.)
Here’s a few things to try first:
- Reset. If troubleshooting led you to a tripped circuit breaker, all you have to do is a quick breaker reset!
- Check the power source. Is your AC a real energy zapper? Try setting your thermostat to AUTO instead of ON to use less energy.
- Clean up time. Your AC may only need cleaning, not repair. Check for debris on or around your outdoor unit, replace dirty air filters, and if you’re a skilled DIY-er, clean your condenser coils and fan blades (carefully!).
Sometimes the best approach is a professional one. If your journey down DIY road didn’t quite pan out, it’s probably time to call an HVAC pro.
Think it might be time to replace your HVAC system? Typically, you’ll need $5,000–15,000 upfront and out-of-pocket for your AC alone (and that doesn’t include any ductwork repair or a new heating system), but there are other options.
Heat pumps are the most efficient, best alternative to a traditional HVAC system. (Curious? Check out our complete heat pump guide).
But don’t let the name fool you. Heat pumps got their name because they remove indoor heat and transfer it outside. They cool your home in the summer months, and then, they heat your home in winter by reversing the process.
Plus, heat pumps dehumidify and purify your home’s air while using as little as ⅓ the energy of traditional HVAC systems—totally why we’ve dubbed them the Tesla of HVAC.
Find out if you qualify for a heat pump upgrade at no upfront cost.
Why sealing and insulating your home can help keep your air conditioner cool
Did you know AC units aren’t the only thing that keeps your home cool and comfortable?
There are two key upgrades that work together to keep your home feeling great year-round while also cutting energy waste: air sealing and insulation.
How do air sealing and insulation work to keep your house cool?
- Air sealing seals every nook and cranny in your house to stop a stuffy, hot in summer and drafts in the winter. A properly sealed home also improves your air quality and lowers humidity levels. Learn more about air sealing in our complete guide here.
- High-performance insulation protects your home against uneven temperatures, no matter the weather. Added bonus? It also keeps out unwanted noise. Make sure your insulation is up to the job with our total insulation guide.
And both of these important home upgrades actually reduce the work your air conditioner does, so its lifespan is longer and your home stays cooler on the hottest of days (with less energy used!).
Learn how to get the upfront costs covered to make your house more comfortable and efficient all year long.
49% of homeowners don’t know that most home energy waste is related to heating and air conditioning. (And air sealing and insulation can help stop it!)
—Sealed Wakefield Research US Homeowner Survey 2021
Frequently asked questions
Check out the list of FAQs below and use the links to jump ahead if needed.
Don’t see your question here? Talk to us. We’re here to help!
- Why is my AC running but not cooling?
- How do I fix my AC not getting cold?
- How do you know your AC has a cooling problem?
- How do I control the air in my AC?
- How do I get a new AC system at no upfront cost?
Why is my AC running but not cooling?
If your AC unit stopped blowing cold air, odds are it’s summertime. That means weeks of unbearable heat if you don’t troubleshoot the issue. So what’s causing it?
Here are 9 common causes of an air conditioner that’s running but not cooling:
- Thermostat settings aren’t set correctly
- There’s a refrigerant leak
- AC coils need to be cleaned
- Air filters need to be replaced
- A compressor malfunctioned
- Outdoor AC unit is clogged
- There’s a duct leak
- The circuit breaker is tripped
- Your AC unit is older and needs to be replaced
Is all the summer heat in your house traveling upstairs? Learn how to get rid of uneven temperatures in your house.
How do I fix my AC not getting cold?
There are two ways to go about fixing your AC: DIY or professional help. Once you’ve figured out the root cause of your AC unit’s warm-air problem, you may be able to fix it on your own.
You can try resetting your tripped circuit breaker, setting your thermostat to AUTO instead of ON, removing debris from your outdoor unit, or if you’re feeling extra crafty—clean your fan blades (carefully!).
However, sometimes it simply takes a professional touch. Want to learn more about getting a modern HVAC upgrade at no upfront cost? We can help.
How do you know your AC has a cooling problem?
Troubleshooting an AC cooling problem can be tough. Here are a few fail-safe ways to get started:
- Make sure your thermostat is set to AUTO
- Check your air filters. Do they need to be replaced?
- Look for signs of AC malfunctions like shaky or noisy outdoor units, or moisture around your AC system
If you still haven’t found the culprit, it may be time for help from an HVAC pro. Need help finding a trusted contractor? Give us a call.
How do I control the air in my AC?
Thermostat settings are often one of the main causes of an AC blowing warm air, and the issue isn’t just uncomfortable—it can waste tons of energy!
Change your thermostat settings to AUTO to stay in control of the air in your AC and help control energy waste at home.
Not for sure if your house and AC are actually wasting energy? Learn the signs of energy wastage.
Is your AC not blowing cold air? We’ve got the perfect fix.
Are you over summer heat? The Sealed team can help.
Your house may be eligible for an energy-efficient upgrade plan from our comfort and climate control experts, at no (or very little) upfront cost.
If you want to update your old HVAC system or simply make it feel great all year, our customized plans are tailored just for your home’s needs. Plus, our whole-house approach has been proven to cut a home’s energy use by up to 50%.
We take care of everything: creating your custom plan, hiring certified home performance contractors, and (most importantly) making sure the work gets done right.
Discover for yourself how amazing your house could feel after working with Sealed. It’s as simple as taking a two-minute quiz to see if your home qualifies.