Why Is My Air Conditioner Blowing Warm Air?

Summer is in full swing. While barbecues and pool parties are great ways to enjoy the summer season, we all rely on the comfort of our homes to provide a much needed respite from the heat.

This is when we count on our air conditioners the most. This is also the busiest season for HVAC technicians. We receive calls concerning ACs blowing warm air every single day of the summer. Luckily, it’s a common HVAC malfunction that can sometimes be resolved by the homeowner.

If you’ve been asking yourself, “Why is my air conditioner blowing warm air?” Service Champions wants to help. If, however, it ends up being something you can’t diagnose or fix on your own, contact Service Champions for all of your air conditioning needs and questions.

How to Troubleshoot an Air Conditioner That Blows Warm Air


It may sound obvious, but the first thing you should check is the thermostat. If your AC is blowing hot air, the thermostat may have been accidentally set to “heat.” If this is the case, it’s easy to fix on your own. Simply flip the thermostat setting back to “cool” and see if the air conditioner begins to blow cool air again.

Additionally, you want to make sure that the batteries are working and that the temperature is not set too high. Remember, the “auto” function only utilizes the fan when air is being heated or cooled. The “on” function means the fan will run 24/7 to circulate the air, even if the AC or heater is off. We recommend using the “auto” function most of the time and only switching to “on” when needed.

The Fix: Check the thermostat and make sure it is set to “cool” and at the proper temperature. If it needs new batteries, replace them. During the cooling season, we recommend setting the thermostat to around 78 degrees Fahrenheit and 7-10 degrees higher while away from home. If the setback period is 8 hours long, you can save 10% on your annual heating and cooling costs (U.S. Dept. of Energy).

Do you need to upgrade your thermostat? Learn how to choose the right thermostat for your home.

Circuit Breaker

After checking the thermostat batteries and setting, make sure the HVAC system has power by checking the electrical panel. HVAC units require a lot of power to run. When there is too much power demand, the circuit breaker may shut off power automatically as a safety precaution.

The Fix: Locate your electrical panel and look for a tripped breaker or a blown fuse. To turn the power back on to the unit, flip the breaker completely off (opposite direction of all the other breakers), and then flip it to the “on” position. If you have a blown fuse, you will need to replace it. This may also be a good time to label all of your circuits for easy reference the next time there is an overloaded circuit.

If your breaker continues to trip for seemingly no reason, you will need to contact a professional HVAC technician or electrician.

Evaporator Coils and Air Filter

Although air filters have nothing to do with air temperature, a dirty air filter can lead to a dirty evaporator coil. When the evaporator coil gets clogged with dust and debris, there may not be enough free airflow to allow for proper cooling operation. A dirty air filter causes debris buildup which can lead to frozen evaporator coils. You may think that “frozen” equates to cool air, but the frozen coils actually impede the flow of cool air, which can lead to warm air flow from the running motor instead.

Air filter replacements should be completed by the owner every 30-60 days, depending on the climate, filter type, and household. We recommend setting a monthly reminder to check the condition of your air filter at the start of every month. If light barely passes through the filter when you hold it up to the light, you should replace it with a fresh one.

The Fix: If your evaporator coil is frozen, turn the unit off and change the air filter. Wait until the unit has thawed before turning it back on again. If the coils freeze up again, turn the unit off and immediately call a professional HVAC technician to troubleshoot the problem. You may have a refrigerant leak or a problem with the compressor – you will need professional assistance.

Condenser Coils (Outdoor Unit)

If you’ve checked the thermostat, breaker box, air filter, and indoor coils, it’s time to go outside to inspect the outdoor unit. Just as the indoor evaporator coils need free airflow, so do the outdoor evaporator coils. That’s why it’s recommended to maintain a minimum 2-foot clearance around the outdoor condenser unit at all times.

The Fix: If your outdoor unit is clogged, turn off the unit at the source. Then, remove the larger items with gloved hands and rinse off the smaller debris with your garden hose. Learn step-by-step how to clean your outdoor condenser unit.

Remember to schedule a professional air conditioning tune-up and cleaning at the start of every cooling season. Double-check that your HVAC company includes full indoor and outdoor coil cleanings as part of their regular tune-up. In addition to professional cleanings, it’s a good idea to periodically check the outdoor unit and clean it yourself when necessary.


One of the main causes of a malfunctioning air conditioner is low refrigerant. If you have a worn service valve, loose joints, or poor assembly, you could have undercharged or overcharged refrigerant.

The Fix: Refrigerant (aka coolant) is highly dangerous. Unless you are a qualified technician, you should never try fixing refrigerant problems yourself. The best way to prevent refrigerant leaks in the first place is to schedule annual air conditioning tune-ups before the cooling season begins. If you do notice your AC blowing warm air, hissing/gurgling noises, or ice on your refrigerant line, act quickly. The sooner you respond to under or overcharged refrigerant the better. Contact your local HVAC company as soon as possible.

Important Note: Do not trust a technician who simply adds refrigerant. Since refrigerant operates on a closed loop system, if you are lacking refrigerant, it means there’s a leak somewhere. Your HVAC technician should repair the leak before adding any refrigerant. If the leak isn’t repaired, you are simply delaying the problem, not fixing it.

Additional Summer Air Conditioning Tips:

  • Keep your thermostat at 78° while at home and 7-10 degrees higher while away.
  • Use your ceiling fan to feel around 4° cooler.
  • Prevent moisture problems with proper ventilation.
  • Sign up for a home maintenance plan so you never forget annual tune-up appointments.
  • Set reminders to check your air filter every 30 days.
  • Keep doors and windows closed when running the air conditioner.
  • Clean and dust your home regularly.

Get help from an AC Expert in Northern California

Service Champions is known for trustworthy, on-time home service throughout the East Bay, South Bay, and Sacramento areas including Pleasanton, San Jose, Concord and more.

For more information on taking care of your HVAC system this summer, contact us today.

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