7 Common Reasons Why Your Home AC is Blowing Warm Air

Kenneth Wilson

Is your home's air conditioner blowing warm air intermittently? While this isn't a rare or uncommon AC problem, there are plenty of possible reasons why your AC unit is blowing hot air.

It usually suggests something's not quite right with your air conditioner. Let's dive right into some of the most common issues why your central air conditioning system is blowing warm air (and what you need to do).

7 Causes of an AC Unit Blowing Warm Air

Here are some of the most common reasons your air conditioner is blowing hot air intermittently (when it should not).

1. Thermostat is Incorrectly Set

Yes, you read that right. Sometimes, your thermostat may be set incorrectly, whether you're aware of it (or not). If your AC starts blowing warm air, you may want to double-check the thermostat to ensure it isn't on heat.

You may also want to see if the thermostat is set to either auto or ON. The fan will continuously blow even if the air conditioner isn't cooling if it's set to ON. Your AC blows out warm air into your home when the outside unit vents aren't running.

2. There is an Airflow Restriction

There may be insufficient air from the vents if there's an airflow restriction to and from the AC unit. As a result, your air conditioner cannot adequately cool your home. A restricted airflow may also lead to the outside unit's compressor freezing up.

Generally, airflow restriction is a result of the following:

  • A dirty air filter that hasn't been replaced in a long time
  • An AC unit that hasn't been appropriately serviced (dirty coils)

3. The Outside Unit is not Getting Power

Your AC system is composed of two main components: an outdoor and an indoor unit. The indoor unit holds the fan that blows air into the home, but it may only provide cold air if the outdoor unit is functioning well.  

Once warm air blows out of the vents– the circuit breaker may have tripped, or the fuse may have blown on the electric circuit that supplies power to the outdoor unit. That said, have the circuit breaker or fuse panel checked by a professional to ensure the circuit is supplying adequate power to your outdoor AC unit. This will help you avoid dealing with significant issues.

4. Obstructed Condenser Unit

If the outdoor condenser unit is blocked or obstructed by leaves (or other debris) in the fall, your AC may also intermittently provide warm air. The condenser unit is responsible for releasing and collecting heat, depending on how you use your HVAC system for the season.

Once you notice intermittent warm air from your air conditioner, ensure that there are no obstructions on your outdoor unit. When left overlooked, it may lead to more costly AC repairs, which means more significant expenses on your end.

5. Blocked Registers/Vents

On a related note, your AC may also give off fluctuating warm air if the cooled air cannot get through the registers or vents. Ensure that every opening of your home’s central AC system is clean and clear, not blocked by several pieces of furniture.

6. Clogged Filter

Are you struggling to remember the last time you changed the filter of your central AC system? If that's the case, it may be time to change it. A clogged air filter can be why your AC unit blows intermittent warm air, as the system may struggle to push cooled air through the obstruction.

7. Central AC is no longer Efficient

Intermittent warm air may suggest it's time that you install a new AC system. This is especially true when the unit exceeds its average life expectancy and requires frequent repairs.

If the AC unit wasn't correctly sized for your home needs in the first place, you'd be better off with an appropriately sized AC system that provides more consistent cooled air.

Other Causes of Intermittent Warm Air from Your AC Unit

Most homeowners dealing with fluctuating warm or hot air issues with their AC unit are likely to be dealing with a compressor or outside unit problems. In some cases, the issue points to an air conditioner low on refrigerant. Other possible causes include a broken or disconnected return duct, which pulls in unconditioned air. All these issues can be handled by an HVAC repair professional. (Related: Seven Common Problems In Your Home’s AC System That Would Cause It To Blow Warm Air (With Solutions))

When to Seek an AC Professional for Help

Here are some issues to be mindful of, which may require you to contact a local HVAC repair professional.

  • Low refrigerant (refrigerant leak): An AC unit with low refrigerant is almost always because of a leak in the refrigerant lines or coils. Keep in mind that only certified professionals must handle refrigerant as it is a potentially toxic substance. Exposure may lead to serious health problems for you and your family.
  • Dirty evaporator coil: If your evaporator coil is covered in dirt or grime, your refrigerant may be unable to absorb that much heat. You'll notice more warm air blowing right into your home. You should leave this issue to an HVAC professional as coils are very delicate. These will require specific tools to clean, and the last thing you want is to damage the AC system further.
  • Leaky or disconnected air ducts: Duct leaks are a common issue among homeowners in the country. A home may lose 20 to 30% of the air that circulates through the duct system due to leaks or any disconnected ductwork. You may want a professional's help to assess your ductwork and repair any leaks. They will be able to fix the problem even if it is located in hard-to-reach areas.
  • Liquid pools: Suppose you detect liquid leaking near your HVAC unit. In that case, best call a technician. This almost probably indicates a low level of freon, a refrigerant leak, or both. Leakage might also tell that your AC compressor is failing, which is one of the causes of the unit blowing hot air. Whatever the reason, this is a complex problem to solve since it involves chemicals.
  • A frozen air conditioner: Your AC unit can be freezing. In severe circumstances,  the evaporator coil might freeze solid. The coil prevents any cold air from entering your home when this happens, and the motor just blows hot air out. This is usually caused by setting the thermostat to the maximum setting and having the air conditioner go from completely off to ice-cold too fast. Still, it might also be a sign of severe thermostat problems. If your air conditioner starts blowing cold air but then shifts to warm after a short period, you have this problem. A professional AC specialist should check this one out.

Final Words

There are no good reasons for your air conditioner to break, but having it start blowing hot air when you least expect it on a hot summer day could be the worst.

Keep in mind that an AC unit is not supposed to blow warm air on an intermittent basis. Contact a local HVAC professional at once when you notice that your AC unit is not evenly circulating cool air (like it's supposed to).

Kenneth Wilson
May 5, 2022

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.

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