Air Conditioner Blowing Hot Air? 5 Common Causes & How to Fix It Fast


When you turn on your air conditioner, the last thing you expect it to do is start blowing out hot air. When temperatures are on the rise outside, that’s when you rely on your air conditioner to cool your house off the most. It’s also the busiest time of year for HVAC technicians. And, one of the most common calls we get is about AC units blowing hot air.  

Fortunately, an air conditioner blowing hot air is a common issue that you can often diagnose and resolve on your own - and even avoid a service call altogether! By following the tips in this guide, you could be having your air conditioning system blowing refreshing icy air again in no time.

Why is My Air Conditioner Blowing Hot Air?

Here are 5 reasons your air conditioner might be blowing warm or hot air and how to fix it:

1. Thermostat is set incorrectly

This may sound obvious, but you never know if someone didn’t accidentally set the thermostat settings to “heat.” So, that’s always the first thing you should check if your AC is not blowing cool air as expected. Additionally, make sure the fan is set to “auto” and not “on.” If it’s set to “on” it will blow air continuously, even when the air conditioner isn’t cooling the air, so it will blow non-cooled air through the vents, too.

2. Dirty air filter

After you’ve verified that your thermostat is correctly set, the next thing you should do is make sure your air filter is clean. When your air filter is dirty and clogged, air cannot properly move through the system. This can lead to your AC blowing out hot air, among other problems. If your air filter is very dirty, replacing it with a new one should restore normal airflow and fix the problem.

AC Blowing hot? Check your air filter

3. Clogged drain lines

Air conditioners work by taking humidity out of the air. That moisture is then sent through the air conditioner’s condensate drain lines. If they get clogged with dirt or dust, this moisture can eventually lead to excess moisture in the system which can cause it to shut down. Clogged drain lines are fairly simple to clean.  

4. Frozen evaporator coils

The evaporator coils in your air conditioner are responsible for extracting the heat from the air and are a crucial part of the cooling process. If moisture collects in the coils, either from dirt, dust, or debris, they may freeze. And, while ice sounds like it should help cool the air, it actually stops the air circulation and causes the AC unit to malfunction. 

Check your interior unit for frost or ice on the coils. You will usually find it just inside an access panel or door. If you find ice, the best option is to turn off your air conditioner and give the unit time to completely defrost. This can take anywhere from a few hours to 24 hours. Do not attempt to run your air conditioner until it is completely defrosted. For one, it will not blow cold air. And, you will run the risk of further damaging your AC unit. Once it defrosts, it should work properly again.

If you find that your evaporator coils are freezing, schedule a maintenance service with an HVAC technician to find out the cause. 

5. Dirty condenser coils (outdoor unit)

You’ve checked the thermostat, the filter is clean, all the breakers are on, and none of the interior coils appear to be frozen. Your next step is to go outside and check the outdoor condenser unit. Just like the evaporator coils inside need to have airflow, the coils outside do, too. So, make sure there’s nothing outside blocking airflow around your condenser. Check for damage to the coils and brush or debris on the outside unit. It should always have two feet of “breathing room” around the condenser to allow for constant air circulation. 

When to call the AC Repair Company 

If none of the above quick fixes have your air conditioning unit blowing cold again, you’ll need to call an HVAC technician to have a closer look at your system to diagnose the problem. It could be any one of these less common problems:

  • Refrigerant leak

  • Failed compressor

  • Fans not spinning

  • Other mechanical problems

For those of you living in Crestview, Choctaw Beach, Niceville, Valparaiso, or Laurel Hill, Florida, rely on the experts at AC by DC LLC. You'll find that our HVAC company can do it all, from AC system installation to duct cleaning. You'll appreciate that we guarantee the quality of our repair and maintenance services. But don’t take our word for it, listen to what your neighbors are saying!