Why Is My AC Blowing Warm Air?

In some cases, a homeowner can comfortably handle inspecting the challenges that can cause an AC to dispense hot air. Other situations mandate that a trained technician fix the problem. Our list of top reasons your AC is distributing warm air begins inside the home. 

Thermostat setting

Let’s start simple. Double check that your thermostat is working properly and is set to the correct setting. To keep your home cool during the summer months, you’ll want the device set to “cool” and “auto” to create the most comfortable environment.

The “auto” function only makes use of the fan when the air in your home is being heated or cooled. The “on” setting means you’ll utilize the fan non-stop until you change the function. In this case, the sound of the fan running may lead you to believe the air is being cooled, but that’s not necessarily the case. When only the fan is operating, it circulates the air in your home without cooling it, which can make it feel like your AC unit is blowing hot air.

Pro tip: Go with a smart thermostat that can be programmed to adjust your home’s temperature based on the time of day. You’ll save energy, and the technology in some smart thermostats can sense a malfunction within the system, alerting you to the problem.

Power to the unit

Your home’s HVAC system requires a large amount of power to operate. When the unit tries to pull too much power, the circuit breaker may flip as a safety precaution. Head to your electrical panel to ensure the breaker is “on” and the unit is receiving electricity.

If warm air is blowing from your split air conditioner, ensure the outdoor unit is receiving power. When the indoor component is the only one working, the system can’t complete the cooling process and warm air will be distributed throughout your home.

If the breaker continues to flip “off” when the AC unit powers up, leave the unit off and call an HVAC technician for a professional fix.

Pro tip: Take a few minutes to label each circuit in your electrical panel. This will make it easier to check the power of your AC unit in the future.

Dirty air filter

The air filter in your home is tasked with catching dust, pollen, pet dander, germs, and other pollutants floating in the air. If the filter becomes clogged, air can’t move through the system as needed. The filter should be replaced every 60 to 90 days, depending on the manufacturer’s recommendations and your indoor air quality.

Low air flow means the outdoor unit can’t properly complete the cooling cycle. The result: an air conditioner blowing hot air into your space. Being uncomfortable isn’t the only problem caused by low air flow. The evaporator coil in the HVAC can freeze over, causing further damage to the system.

Pro tip: Use a marker to write the date on the filter when you change it. This will keep you on schedule to replace it regularly.

Frozen evaporator coil

The evaporator coil absorbs the heat energy from the air in your home. It’s housed in the outdoor unit and works with the condenser coil to return cool air into your space.

The coil depends on strong air flow for proper cooling operation. A dirty air filter or clogged evaporator coil will cause the component to freeze, blocking cool air from returning into your home. 

In severe cases, the outdoor unit may have frost visible from the outside. If you don’t notice signs of freezing, open the front panel of your outdoor HVAC unit. The evaporator coil may have a small amount of ice or frost or could be completely encased. 

If you just replaced a dirty air filter and feel it may have caused the frozen evaporator coil, allow the unit to thaw. The process could take up to 24 hours, depending on the severity. Once you’ve thawed the unit, turn the AC back on. If it begins freezing again, call in an HVAC technician.

Pro tip: Schedule seasonal maintenance to have the evaporator coil cleaned. This can help prevent the component from freezing in the future.

Low AC refrigerant

The HVAC system that cools your home uses refrigerant, or coolant, to complete the process. The chemical is responsible for transferring the hot energy from inside your home to the outdoor unit to be cooled. The refrigerant then delivers the cool air back indoors.

When refrigerant is low or there’s a leak in the system, it will feel as if your AC is blowing hot air. Consider the last time the HVAC unit was serviced. If it’s been a while, or if you just moved into a home, schedule a maintenance appointment to have the system evaluated and refrigerant level checked.

A refrigerant leak may be possible if your outdoor unit is making a hissing or whistling sound. The refrigerant will leak out, making it impossible for the AC to cool your home. A technician can replace the torn line, refill the refrigerant, and recharge (or pressurize) the system. The Environmental Protection Agency mandates that only a certified technician can recharge your home’s HVAC unit, so leave this repair to the pros.

Pro tip: Keep a calendar for your HVAC maintenance dates. This will help remind you every 6 to 12 months to have a tech come out and service your unit and check the refrigerant level.

Blocked condenser coils

Dirt, leaves, and other debris can build up around your outdoor HVAC unit. When those bits and pieces get lodged inside the condenser coils, your unit can’t complete its job. The condenser coils are those small wire holes that make up the outside shell of your outdoor unit. Keeping them clean allows for proper air flow and a cool home.

If it sounds like your outdoor unit is running, but the AC is blowing out hot air, start with cleaning the condenser coils. Remove any large pieces by hand, then rely on a home AC coil brush to clean out the debris stuck between the coils. 

Spray the coils with a water hose, clearing away the loose dirt and foliage. You can also use a coil cleaner on the unit to remove caked on grime. Let the solution sit for 5 to 10 minutes, then wash it away with the hose. If the AC continues to blow warm air, call an HVAC expert for help.

Pro tip: Remove foliage from around your HVAC unit when you perform yard work. This will prevent the debris from finding its way into the condenser coils.

Repair AC Blowing Warm Air

Tackle the small tasks first, checking your thermostat setting, filters, and power to the unit. The hot air blowing from your HVAC system may be a simple fix.

In the event that your unit needs to be repaired, consider if the repair cost is worth the investment or if it’s better to put that money toward replacing the unit. To help you decide, consider:

• Age of unit (12+ years is nearly max lifespan)
• Recent repairs
• Efficiency of unit
• Cost of repair vs. replacement

Schedule routine maintenance for your system to ensure it lasts for years to come.

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