Common Causes of A/C Blowing Warm Air

Spring is here and warm weather is not far behind. Have you recently tried to turn on your air conditioning and noticed your vents are blowing warm or hot air? Many people set their thermostat to their desired temperature only to find out their house is not cooling down. When you rely on your cooling system to keep your home and your family comfortable, this can be an extremely frustrating situation. So let’s get down to it and answer the question – why is your A/C blowing warm air?

Your AC is blowing warm air because while the fan is operating, something is shutting down the cooling mechanism. Causes include simple things like thermostat settings and poor air flow, but also could be issues that can spell big trouble, like electrical problems or refrigerant leaks. We’ll provide solutions for simple steps to attempt to fix the problem yourself, however, if the problem persists, Michael & Son is here to take care of all of your heating & cooling needs 24/7 at 800-948-MIKE.

1. Thermostat Problems

The first thing to check should be your thermostat. In many households, settings get tampered with by children horseplaying, or someone turning it off because they are too cold. It is important to make sure the thermostat is set to COOL and the fan set to AUTO. Also, make sure that the set temperature is, in fact, lower than the ambient room temperature. If your thermostat still isn’t working after checking these simple fixes, you could have a larger issue such as improper wiring. Contact Michael & Son to properly diagnose the issue should you encounter further issues.

2. Return Vents Blocked or Closed

Many times, vents are closed during the winter. Take a moment to locate the vents around your home and make sure that all registers and returns are open and that there is no furniture blocking the vents that would obstruct the flow of air. If you open your vents and there is still weak or no air blowing through them, you may have a much larger problem with your system’s fan.

3. A Clogged HVAC Filter

Reduced air flow is a very common problem that impedes the cooling operation of your AC. You might be surprised to learn that your air conditioner needs warm air flowing over the coils in order to function properly. The AC filter is designed to remove dust and contaminants from the air flowing through the equipment. Therefore, a clogged air filter completely blocks air from entering the system. In this case, the coils can’t remove heat. In closing, your system’s fan will only be able to blow hot air until this is taken care of. If you haven’t had your system maintained in a while and your AC is blowing warm air, the next step is to check and change your air filter if possible. If the problem persists after a filter change, you may need to consider an A/C tune-up and coil cleaning.

4. Refrigerant Leak

Refrigerant is the liquid mixture that flows through your AC system and creates cooling. It’s a closed loop, therefore adding refrigerant is unnecessary unless there’s a leak in your refrigerant line or the coils. This causes your system to lose refrigerant charge and cooling power. Also, depending on the size of the leak, the cooling loss can happen very slowly or all at once, but your AC will eventually blow warm air.

Remember you can not add your own refrigerant. This will only create a bigger problem. Additionally, if your system uses the refrigerant Freon (which is likely if it’s older than 8 years or so) that refrigerant is being phased out as per the EPA January 1, 2020. That means it will get increasingly expensive to fix, and you will need to think about replacement in the near future.

5. Loss of Power to the Outdoor System

There are many AC units that have an indoor evaporator/air handler system and the outdoor condensing unit. The fan will still blow air into your space when it is working. Moreover, if the condenser unit is not working properly your AC will blow cool air. This also happens when your condenser unit loses power, often due to a blown fuse or tripped circuit breaker.


Never try to diagnose electrical issues yourself unless you are a trained electrician or HVAC expert. Live voltage is extremely dangerous and not something to toy with. You can check your emergency shutoff switch. At times this may accidentally shut off, cutting the power to your condenser unit and leading to your AC blowing warm air.

6. Disconnected or Leaky Ducts

If the ducts in your home have holes, cracks, or have become completely disconnected, return air may not be making it back to the unit. Additionally, cooled supply air may be getting pushed in your walls, attic or crawl space, resulting in your air conditioning blowing warm air through your home.

If your ducts are exposed or accessible, such as in your attic, crawlspace, or basement ceiling – visually inspect them to check for damage. It’s common for damage to occur during construction projects, or from birds or other animals getting into the ductwork. If you suspect there is an issue with your ducts, getting a professional to take a look at these ducts is highly recommended.

Call Michael & Son at 800-948-MIKE to have a professional assist with any of your HVAC needs. Be sure to check in with us weekly for more home improvement and safety tips. Also, like us on Facebook, follow us on Twitter and subscribe to our YouTube page to stay up to date on upcoming events, great savings and much more!