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Why Is My AC Blowing Warm Air?

The warm and humid Minnesota summers require a reliable AC that keeps your home comfortable and cool.

But what about when your AC starts blowing warm air?

Most likely, the cause of the problem is one of these reasons:

Let’s take a closer look at each issue and which ones you can resolve on your own and which might require professional help.

Want a professional to inspect your air conditioner? MSP’s trustworthy technicians offer same-day AC repairs to get your system back up and running in no time.

You Accidentally Set Your Thermostat Incorrectly.

Check that your thermostat settings aren’t on HEAT.

Check that your thermostat settings aren’t on HEAT.

Before assuming your AC needs repairs, ensure you’ve set your thermostat to COOL mode and AUTO.

You may have accidentally switched your system to HEAT mode instead of COOL mode, or perhaps you forgot to adjust it after the seasons changed.

If the thermostat is already on COOL, but your air conditioner’s fan is blowing, and the air feels warm, check to see if the ON setting is activated. Your thermostat's ON setting means the fan will stay on all the time, even when your AC isn’t actually cooling your home. The ON setting continually circulates air throughout your home, even when the AC isn’t actively cooling the air. That might explain why you’re feeling warm air coming out of the vents sometimes.

To fix that, make sure to set your thermostat to AUTO to ensure that your AC’s blower fan only pushes air into your home during the cooling cycles instead of all the time.

Dirt Is Clogging the Filter.

Change out your air filter whenever it’s dirty.

Change out your air filter whenever it’s dirty.

A dirty filter will restrict airflow to your AC system and may cause the evaporator coil to freeze up, keeping it from cooling your air.

The evaporator coil is a part of your indoor AC unit. Its job is to release the heat absorbed by the refrigerant, a chemical agent within the coil, into the outdoor air. For this process to properly work, the refrigerant needs to absorb heat from the warm air flowing over it. But if the air filter is dirty, it won't be able to do so as effectively.


Your AC’s air filter protects your air conditioner by removing large dirt particles and debris from the air and allows filtered warm air to enter the system. But, if you leave a filter in there too long, it gets filled with dirt, restricting airflow to the system. A lack of warm air moving over the evaporator coil in your indoor unit can make the refrigerant inside it very cold, and it may eventually freeze over. As a result, your AC won’t be able to cool your home correctly.

If you think the cause of your AC problems might be a dirty filter, you should replace it with a new one right away. Then, let your air conditioner run for a bit and see if the air blowing out feels any cooler. If it doesn’t, it’s best to contact an HVAC technician. They can inspect your AC, diagnose the problem, and recommend any necessary repairs.

Your AC Is Low on Refrigerant.

If your AC is low on refrigerant, your AC won’t be able to blow cold air.

If your AC is low on refrigerant, your AC won’t be able to blow cold air.

Refrigerant is a liquid substance that removes the heat from your home’s air. If your AC is low on refrigerant, it will struggle to cool your home.

Additionally, refrigerant cycles through your AC system in a closed loop, so if your AC is suddenly low on refrigerant, there's a leak somewhere that a contractor needs to repair.

Other signs of a refrigerant leak include:

  • A hissing or bubbling sound
  • Water pooling around the indoor unit
  • Higher utility bills
  • Ice on the refrigerant line

An experienced HVAC technician in the Minneapolis area can inspect your AC to locate the leak, repair it, and recharge your AC with the correct amount of refrigerant.

The Evaporator Coil Is Dirty.

Evaporator coils help absorb heat from your indoor air.

Evaporator coils help absorb heat from your indoor air.

The evaporator coil inside your indoor AC unit contains refrigerant, which absorbs heat from the air that blows over the coil. If the evaporator coil gets covered in dirt, it will prevent the refrigerant from absorbing heat, causing the air coming out of your vents to feel warmer.

Extensive dirt buildup on the evaporator coil typically occurs when your AC isn’t regularly maintained and cleaned by an HVAC professional. Although you might want to clean the coils yourself, they are fragile and easily damaged if not handled properly. Plus, AC cleaning requires special tools, so we recommend hiring a well-trained technician to do it for you.

The Compressor Is Malfunctioning or Failing.

The compressor pumps refrigerant throughout your system.

The compressor pumps refrigerant throughout your system.

Issues with your compressor will inhibit the cooling process, resulting in warmer air coming out of your vents.

The compressor is inside your outdoor AC unit, and it pumps the refrigerant through your system. As your AC ages, the compressor may start to fail, and your system won’t cool your home as well as it used to.

Alternatively, if the compressor is malfunctioning in some way, the cooling process will still suffer, and it may cause additional wear and tear on other components of your AC. Aside from warm air coming out of your vents, other signs of a malfunctioning compressor are:

  • Loud noises coming from your outdoor AC unit
  • Weak airflow coming out of your vents
  • AC circuit breaker keeps tripping

It’s a good idea to hire an HVAC professional to determine whether the compressor is the cause of your AC problems. They will inspect the compressor to ensure that it’s working correctly. If it’s not, they may recommend replacing it. However, since the compressor is typically expensive to replace, it may be better to replace your air conditioner. A reliable technician can provide honest recommendations based on your budget and your AC’s current condition.

MSP AC technicians are ready to help you cool your home.

MSP AC technicians are ready to help you cool your home.

Need a Twin Cities Professional To Repair Your AC?

Minneapolis Saint Paul Plumbing Heating Air can help! We offer same-day AC repair service, and you can trust that we only hire professional and courteous technicians who clean up after themselves. With a reputation for honest, upfront pricing and ironclad satisfaction guarantees on our work, we’ve earned the loyalty of our customers for more than a century.