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Why is my air conditioner blowing hot air?

May 07, 2019

Why is my AC blowing warm air?

air conditioner remote control

As the temperature rises outside, people across the Washington, D.C. metro area are cranking up the AC inside. This all works perfectly until you notice your AC blowing warm air, which is an annoyance many homeowners experience during the hottest months of the year.

Let’s explore some of the most common causes of insufficient cooling in your home: 

3 Reasons Why Your AC Is Blowing Warm Air

1. Incorrect Thermostat Setting

If you notice your AC blowing warm air, the first step is to check your thermostat. It seems obvious, but an incorrectly set thermostat is one of the most common reasons for insufficient cooling. 


Maybe your thermostat reset after a power outage, or perhaps you powered down the AC and opened a window for some fresh air, only to forget to turn the cooling back on after the window had been closed. It’s possible to find your AC blowing warm air instead of cooling your home properly because of a simple error with the thermostat, so it’s worth double-checking the settings to ensure the air conditioning is turned on.


You should also check whether the fan setting on your thermostat is set to “auto” or “on”. “Auto” means that the fan will kick on only when your system is heating or cooling. Once your home reaches the desired temperature, the fan shuts off. If your fan is set to “on,” it will continually blow air, even if your air conditioner isn’t actively cooling your home. This can result in your AC  blowing warm air through the vents. Homeowners interested in saving money on cooling should keep the fan set to “auto.”


Read more: 3 Ways to Save Money on Air Conditioning This Summer

2. Tripped Circuit Breaker

Another possible explanation for your AC trouble is a tripped circuit breaker. If your outdoor HVAC unit isn’t receiving electricity, it won’t be able to cool the air in your home. This results in warm air blowing from the indoor air conditioning unit.


Check your fuse box to make sure the circuit supplying electricity to your outdoor air conditioning unit hasn’t tripped. If the circuit did trip, flip the breaker back to the “on” position.


A tripped circuit breaker or a blown fuse is usually caused by a power overload. This could be indicative of a more serious electrical problem, so you’ll want to consult a licensed electrician to ensure the wiring in your home is up to code and can handle the draw of your AC system.

3. Air Conditioning Unit Damage or Malfunction

Your AC blowing warm air could also be caused by internal damage to your unit. While regular preventative maintenance can help you avoid these problems, sometimes age and prolonged use wear down your unit. 


One of these common air conditioning problems could be to blame:

Refrigerant Leak

A typical cause of air conditioning malfunction is a refrigerant leak, which inhibits the unit’s ability to properly condition the air circulating throughout your home. Refrigerant leaks are most likely to occur with heavy air conditioning use at the start of the cooling season, especially if your unit hasn’t been serviced since the previous spring or summer. We recommend scheduling an AC inspection with a qualified HVAC technician prior to turning on your cooling system for the season.

Frozen Evaporator Coil

Surprisingly, one of the most common reasons for your AC blowing warm air is actually a frozen air conditioner — specifically, a frozen evaporator coil.


Warm air from inside your home is drawn into your AC unit and passed over the refrigerant-filled evaporator coil, which removes the heat from the air. The result is cool, conditioned air that is then blown back into your home. As warm air passes over the evaporator coil, condensation forms that is intended to evaporate. However, it’s possible for condensation to build up and eventually freeze. This typically happens on hot days when the AC is cranked up to the highest setting.


This frozen condensation can block airflow through the AC unit and cause the motor to strain and overheat, which results in warm air entering your vents.


If your AC unit freezes up, turn it off and let it thaw. It should be safe to turn back on after an hour or so, but make sure to set the thermostat high and work your way down to a comfortable cooling level. If your unit continues to freeze, you’ll need to contact an AC repair company to run diagnostics.

Clogged Air Filters

Have you changed your air filters in the last few months? Most homeowners neglect to replace their air filters until something goes wrong, and that could be the reason behind your AC blowing warm air


Over time, air filters get clogged with dust and debris, which can reduce the efficiency of your air conditioning system. However, clogged air filters are not solely to blame for an air conditioner that’s blowing hot air.


If you’ve recently cleaned or replaced your air filters and are still experiencing cooling issues, contact an HVAC professional to inspect your system, as there is likely another contributing factor to insufficient cooling.

Damaged Compressor

The compressor is the heart of your air conditioning system. This pump is responsible for moving refrigerant between the evaporator and the condenser, which is critical to the cooling process. Without the compressor, the entire air conditioning unit fails to operate properly, causing the issue of your AC blowing warm air.


Common causes of compressor malfunction include:


  • Electrical failures
  • Refrigerant returning to the compressor
  • Overheating

Unfortunately, a broken compressor can be nearly impossible to repair. In the event that your AC compressor is damaged, you’ll have to replace the part, or replace your AC unit entirely for a newer, more efficient system.

Schedule an Air Conditioning Inspection

CroppMetcalfe offers air conditioning service and repairs across the DMV at manageable costs to homeowners. If your air conditioner isn’t performing adequately, call our 5-Star Technicians at 703-495-2486 or submit an HVAC service request online today.



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