Why is My Home’s AC Unit Blowing Hot Air?


Your home’s air conditioning system contains dozens of parts that must function properly in order to efficiently cool your home. When one part goes out, the whole unit could malfunction. So why might your home’s AC unit be blowing hot air?

This hot air is likely the result of a bad part or a refrigerant leak and will require an AC technician to repair it. Other problems can be repaired or corrected by the homeowner. Listed below are the main causes of hot air being blown from your home’s AC unit:

  1. Refrigerant Leak
  2. Frozen AC Unit
  3. Thermostat Settings
  4. Blown Breaker Switch
  5. Air Filters
  6. Bad Compressors
  7. Bad Wiring

Refrigerant Leak

A refrigerant leak is one of the most common causes for AC units to malfunction. Refrigerants can leak for a variety of reasons, but it’s highly unlikely you will be able to diagnosis the leak.

Unfortunately, there is never one exact reason for a refrigerant leak. Any number of cause can result in a leak such as poor construction from the manufacturer, normal wear and tear over a period of years, or a worn service valve. The leaks are generally random and unpredictable. Turning your AC unit on high after being off all winter can cause damage to the outside unit, causing a variety of wear-and-tear issues.

To prevent the unit from leaking in the future, keep your eye on it and have the unit serviced  by a professional technician before turning it on for the summer or soon after turning it on.

How to fix it: Refrigerants are dangerous and work in a highly pressurized system. Repairing refrigerant leaks should always be left to a professional. Contact a Bunn’s and Bennett air conditioning specialist if you have questions about your air conditioning system.

Frozen AC Unit

Air conditioning units can actually freeze. In fact, this is the most common cause of air conditioners to blow warm or hot air. The frozen part is the evaporator coil, which can block the cool air flowing into your home. Instead, the motor’s heat gives you warm air flow instead as long as the fan is not frozen as well.

Causes and how to prevent it from happening again: Inside of the unit, condensation can occur on the coils which is intended to evaporate. This condensation can build up and freeze if the temperatures at which the AC is trying to blow falls below 32ºF. Typically this happens on a hot day when homeowners turn their AC on the highest setting. To prevent this from happening, you should keep your thermostat on auto around 70 or 72ºF and keep an eye on the unit, inside and out.

How to fix it: First, turn it off and let it thaw. After about two hours, it should be safe to turn it on, but it may freeze again. If it does, then you’ll need to contact Bunn’s and Bennett Heating and Air Conditioning to take a look at it.

Thermostat Settings

Sometimes we forget to turn the thermostat to “cool” from “warm” in the winter. If you or someone in your family accidentally sets it to warm, the unit will start blowing warm air to maintain the temperature instead of cool air.

Make sure the unit’s temperature is not set too high on auto.

Causes and how to prevent it from happening: Often times, homes with young children means things get tampered with either intentionally or unintentionally, and your thermostat is no exception. Others merely forget to switch the setting over. We recommend making a note to yourself before summer comes to turn it on “cool” mode and stick it to the fridge or in your calendar when outside temperatures begin to get warmer.

How to fix it: Check your thermostat and see what mode it says it’s in. Also check the temperature and adjust it accordingly. Better yet, check into installing a programmable thermostat from Bunn’s and Bennett Heating and Air Conditioning.

Blown Breaker Switch

Your home’s outside AC unit has it’s own power supply. This power supply also has an on/off switch that can be tripped by a bad breaker. Without power, the unit simply won’t turn on. The external unit does not need power to circulate the air inside of your home; that’s up to your internal unit, which likely still has power.

Causes and how to prevent it from happening: Breakers may flip off for seemingly no reason at all, but it is usually a power overload. If your AC breaker has too much electrical current, it switches off on it’s own as a safety precaution. AC units require a lot of current from your home and can flip breakers. To prevent it from happening, consult an electrician as well as an AC repair company to ensure your breaker can handle that current draw.

How to fix it: To fix the problem, simply flip the breaker back to the “on” position. If that does not fix it, contact a Bunn’s and Bennett Heating and Air Conditioning.

Air Filters

When is the last time you changed or cleaned the air filter in your AC unit? Most people neglect to until something goes wrong. Air filters do get dirty and this blockage won’t clear up until you or a technician replaces it or cleans it. The filter alone will not cause warm air to blow, but it will contribute to the problem and reduce cooling effectiveness significantly.

Causes and how to prevent it from happening: Air filters are there to catch dirt and debris that may be flowing through your internal unit. If they are doing their job, they become dirty and need to be cleaned or replaced. You should check on it regularly.

How to fix it: Turn the unit off, install a new filter or clean it.


The AC compressor’s job is to take the refrigerant gases from the evaporator and convert it to a hot, high-pressure gas. The gas is then transferred to the condenser. Without the compressor, the whole unit will fail to operate properly, if at all. Unfortunately, the compressor is also one of the most commonly misdiagnosed problems with AC units. For this reason, we recommend calling a professional such as Bunn’s and Bennett to confirm that it is indeed the compressor causing the problem.

Causes and how to prevent it from happening: The compressor could go bad for a variety of reasons, but most common to blame is:

• Electrical failures

• Refrigerant coming back to the compressor

• Overheating

Unfortunately, there’s no way to prevent a compressor from going bad except lighter use. Compressors generally last at least 10 years and can work up to and past 20 years.

How to fix it: Compressors are not units that just anyone can fix, so you’ll have to call a professional to confirm that it is the problem and replace it. If the compressor is too expensive, it may be worth replacing the unit entirely with a new, more efficient system.


Miscellaneous electrical problems might also be the source of hot air blowing from your AC unit. There are numerous wires flowing in out and around the external and internal unit. If one of these wires is frayed, cut, or otherwise damaged, it could cause poor performance or even cause the unit to shut down entirely.

Causes and how to prevent it from happening: Wiring can be frayed if it gets burned by overheating. This is an extremely rare occurrence. Generally, wires are damaged by animals or by family pets. To prevent this from happening, you should make sure wires are concealed. It is recommended keeping both your external and internal units protected from animals with some sort of barrier.

How to fix it: If the wire is broken, you’ll have to contact an AC repair company such as Bunn’s and Bennett to replace the broken wires.

Bunn’s and Bennett is a licensed and insured heating and air conditioning company, serving Huntsville and the Tennessee Valley for more than thirty years. Our awards for service and reliability are numerous, and our goal is to make your home comfortable. Feel free to contact us with any questions at [email protected].

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