AC Not Blowing Cold Air

Few things are more uncomfortable than when your central AC is not blowing cold air on a hot summer’s day. The humidity in your home rises as well when your AC isn’t working right. If your central AC is blowing hot air instead of cold, you’ve come to the right place.

The answer to the question “Why is my AC not cooling?” has several answers. Some of the most common reasons for an AC unit not blowing cold air include:

• Clogged air filter
• Clogged AC condensate drain line
• Dirty condenser coil
• Frozen evaporator coil
• Low refrigerant level
• Thermostat problems

You may be able to resolve a few of these problems on your own, but we recommend working with an HVAC professional for AC repair. This will help ensure that your central air conditioning system is thoroughly checked out and operating safely.

If your air conditioner is still under warranty, this is also the smart way to go, as DIY repairs could void the warranty.

A clogged or dirty air filter can cause reduced airflow or even block airflow. This can cause the AC unit to work harder trying to cool your home. This in turn can cause much bigger problems, such as a frozen evaporator coil. Check the filter and replace it if needed. Get into the habit of changing your filter regularly – generally every 1-3 months.

Refer to our HVAC filter maintenance guide for some tips.

When you ask yourself “Why is my AC not blowing cold air?” check your thermostat before you call for AC repairs.

• Make sure your thermostat is set to cool and didn’t get bumped to heat.
• Make sure the fan is set to AUTO, so the system only blows air when the AC is running. If the fan is set to ON, it will blow warm, unconditioned air even when the AC isn’t running.
• In addition, make sure the temperature you have set is lower than the current indoor temperature.  
• If your thermostat uses batteries, check to make sure they’re working. If the thermostat screen is blank, replace the batteries.

If none of these things resolve the issue, now is a good time to call your local HVAC company.

As your air conditioner cools your home, it also pulls humidity from the air. This water vapor/condensation drips into a condensate pan and then into a condensate drain line. Over time, dust, debris, spider webs, mold, or mildew from standing water can cause a blockage in the drain line.

Some indoor units have a drain pan condensate safety switch that will automatically shut down the indoor unit if the water level inside the drain pan begins to rise. This could be why your AC isn’t blowing cold air. Fixing the issue is best left to a trained HVAC technician.

Your outdoor unit houses the condenser coil, compressor, and other components. Over time, dirt, grass clippings, pollen, and other debris make their way inside the unit. A buildup of dirt and grime on the condenser coil can cause reduced airflow and even a system shutdown.

You can help prevent this by keeping debris off of the top of the unit and keeping plants at least two feet away from the sides of the unit. You may also be able to gently hose down the outdoor coil. For thorough maintenance, call an HVAC professional.

A frozen evaporator coil can also be the culprit if your AC is running but not cooling. The evaporator coil is the indoor coil, located next to your furnace. It is sometimes called the furnace coil or the “A” coil because of its shape.

The evaporator coil is a critical component in the refrigeration cycle. It absorbs the heat from inside your home and transfers it outside. The evaporator coil is also known as the cold coil in your air conditioning system. Air blows across the cold evaporator coil, cooling it before it enters the ductwork system.

Over time, dirt and debris collect on the evaporator coil, preventing proper air circulation. This can cause the coil to frost over, or freeze. A dirty filter can also cause a frozen evaporator coil. If you see visibly frozen coils, turn the system off and contact an HVAC service professional for help.

Another common reason for your AC not blowing cold air is it’s low on refrigerant. This can result from a refrigerant leak or improper charging at installation. In either case, you need an HVAC professional to assess the situation, fix the leak if possible, and recharge the unit if practicable.

Sign up for auto-delivery of air filters, pay attention to what your thermostat says about changing the filter, install the Trane Home App, set an alert in your phone – whatever it takes, do something so you will remember to change the filter.

Consider signing up for an HVAC service plan with your HVAC company. Standard HVAC maintenance plans include an AC tune-up in the spring and a furnace tune-up in the fall. You may also be eligible for certain perks as a valued customer. This regular maintenance can help catch problems while they’re still small and before they turn into big and costly problems.

If your house AC is not blowing cold air, call for AC repair now.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Mark Woodruff, Senior Product Manager, Ducted Outdoor

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