July 30, 2014

Home AC units have dozens of parts that must function properly in order to efficiently cool your home. When one part goes out, the whole unit could malfunction. One common problem many residents notice is that their air conditioner blows warm air. This warm air is likely the result of a bad part or a refrigerant leak and will require an AC repairman to look at it. Here is the FULL list of problems which may cause an AC to blow warm air:

Refrigerant Leak

Sitting at the top of the list is one common cause for AC units to malfunction. Refrigerants can leak for a variety of reasons, but you’re likely not outside to see the leak. If it leaked on Friday, then on Saturday when you are sitting around the house you won’t be able to see the leak outside because it will be empty.

Causes and how to prevent it from happening again: Unfortunately, there is never one exact reason for a refrigerant leak, but it could be that a joint came loose due to heavy use. New AC units may have been assembled poorly by the manufacturer, but this is a rare sight when buying any respected brand (we prefer Lennox and York). Lastly, a worn service valve could cause a leak. The leaks are generally random and unpredictable, but heavy use and turning the AC on high after being off all winter can cause damage to the outside unit, causing a variety of wear-and-tear damages. To prevent the unit from leaking in the future, keep your eye on it and have the unit serviced before turning it on for the summer or soon after turning it on.

How to fix it: Refrigerants are dangerous and should always be left to a professional. Contact your local AC repair company and explain the issue to them.

Frozen AC Unit

To many homeowners’ surprise, air conditioners can actually freeze. Yes, freeze solid inside into a block of ice. In fact, this is the most common cause of air conditioners to blow warm or hot air. The first thought when homeowners see the ice is “Why would it blow warm air if it’s frozen?” The frozen part is the evaporator coil, which can block the cool air flowing into your home. Instead, the motor’s heat gives you a nice (or not so nice in the summer) warm airflow instead, so 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 and 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. Have a service technician take a look at it at the beginning of the summer season as well.

How to fix it: First, turn it off and let it thaw. After about an hour or 2, it should be safe to turn it on, but it may still freeze. If it does, then you’ll need to contact an AC repair company to take a look at it.

Thermostat Settings

Put simply, some homeowners forget that they have to turn the thermostat to “cool” from “warm” in the winter. If you or your kids accidentally set it to warm, the unit will start blowing warm air to maintain the temperature instead of cool air. Also, make sure the unit’s temperature is not set too high on auto.

Causes and how to prevent it from happening: Generally, homes with kids mean things get messed up, 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 for the first day of summer.

How to fix it: Check your thermostat and see what mode it says it’s in. Also, check the temperature and adjust it accordingly.

Blown Breaker Switch

The outside unit has a power supply, as with any appliance that requires power. 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. But 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 that breaker has too much current, it switches off on its own as a safety precaution. AC units suck up 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 repairman. If the breaker is dead entirely, you will need to contact an electrician.

Air Filters

When is the last time you changed or cleaned the air filter in your AC? Most people never do until something goes wrong. Air filters do get dirty and this blockage won’t clear up until you or a technician takes it out and replaces 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, order a new filter or clean it, then reinstall it back to its original position.


By Juan de Vojníkov (Own work) [CC-BY-SA-3.0], via Wikimedia Commons
The AC compressor’s job is to take the refrigerant gases from the evaporator and convert it to a hot and high-pressure gas. The gas is then taken 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 to confirm that it is indeed the compressor that’s bad.

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 it from going bad except for lighter use. However, compressors generally last at least 10 years and can work up to and past 20 years.

How to fix it: Compressors are not parts that 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 could be the source as well. There are a ton of wires flowing in out and around the external unit and internal unit. If one of these wires is frayed, cut, or otherwise damaged, it could cause poor performance or even break the unit down entirely.

Causes and how to prevent it from happening: Wiring can be frayed if it gets burnt by overheating, but this is an extremely rare occurrence. Generally, wires are cut by family pets, such as cats and dogs. If the wire is exposed and they decide to chew on it, the unit will malfunction. To prevent this from happening, you should make sure wires are not sticking out. If they are and cannot be fixed, we recommend keeping both your external and internal units protected from animals with some sort of wall or fence around it.

How to fix it: If the wire is broken, you’ll have to contact an AC repair company to replace the broken wires.

For more heating and AC problems, check out our HVAC blog for more FAQs.

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