When the sweltering summer heat hits, there’s nothing more frustrating than your air conditioner blowing warm air into your home. There are a few reasons why this happens, from incorrect settings to a more complex fault. Let’s explore each possible reason and learn some practical solutions to keep that refreshing cold air flowing.
Culprit #1: Fan Is Set to “On”
The most common reason your air conditioner starts cold but then blows warm air is because the fan setting on your thermostat is set to “On” instead of “Auto.” With this setting, the cooling cycle starts and stops as necessary, but the fans always stay running, potentially sending warm air through the vents.
Setting the fan to “On” is useful if you’re doing something that requires better air circulation and filtration, but it’s best to keep the setting to “Auto” in most cases. When the fan only runs during the cooling cycle, your AC won’t blow warm air.
Culprit #2: Incorrect Thermostat Settings and Malfunctions
Basic thermostats have auto, on, fan, cool, and heat settings. Newer thermostats allow you to schedule temperature settings in advance as the day progresses.
If you’re getting warm airflow from your air conditioner, check your thermostat settings. Change the batteries if they’re running low, and wipe the exterior so dust won’t collect inside. You can also check that the thermostat is properly connected. The back of the thermostat face has prongs, and if they’re missing or bent, they can interfere with normal operation.
If all else fails, ask your HVAC technician if a new thermostat may be necessary.
Culprit #3: Dirty or Missing Air Filters
When the air filters get clogged, your system can’t pull as much air into the air handler, putting more strain on the blower and other essential parts of the air conditioner. This could be one of the reasons why your AC runs constantly.
Missing filters are another significant concern, which can cause the evaporator coils to become clogged with dust, dirt, dander, and hair. Dirty coils can cause your air conditioner to malfunction or even freeze.
The EPA suggests that every homeowner change their air filters at least every three months. However, not every homeowner should wait that long. You should change your air filter as soon as you see that it is dirty.
Culprit #4: Low Refrigerant Levels
Refrigerant plays an important role in your air conditioner. If there’s a freon leak or you have low levels, your air conditioner will struggle to stay at the temperature you need it to.
You can prevent refrigerant issues by having your air conditioner inspected and tuned up a few times per year. Your technician should evaluate the condenser coils, outdoor and indoor units, ductwork, refrigerant levels, fan motors, and refrigerant lines.
Fixing refrigerant-related issues is not a DIY project due to the environmental and health risks involved. Instead, call an EPA Section 608-certified HVAC professional for the job.
Culprit #5: Dirty or Damaged Ductwork
Ductwork damage can cause hot air to blow out of your HVAC vents, decrease your air conditioner’s efficiency, and put more strain on the components.
To prevent ductwork issues, have your ducts professionally cleaned every few years or as needed. You should also consider sealing and insulating ducts if you haven’t already, especially in unconditioned spaces such as attics and crawl spaces.
Culprit #6: Evaporator Coil Problems
The evaporator coil absorbs heat from indoor air. Dirty coils won’t cool air efficiently, and frozen coils won’t cool air at all.
Look behind the air filter to check the coils for damage or ice. If you see any issues, turn your air conditioner off and call a professional for repairs. You should also schedule professional coil cleaning as part of annual AC maintenance.
Culprit #7: Electrical Problems
If one of the components in your air conditioner isn’t getting enough power, it could lead to warm air blowing out of the vents.
Check the circuit breaker by your outdoor AC unit, and reset it if it’s been tripped. Set the disconnect switch near the unit to the “On” position and see if that resolves the issue.
If problems persist, you could have a wiring issue or a faulty capacitor. At that point, there’s too much risk trying to fix the problem yourself, and you should call your HVAC company or a licensed electrician.
FAQs About Air Conditioners
How do I fix my AC that starts cold then gets warm?
First, check your thermostat’s fan setting and make sure it’s on “Auto.” If that doesn’t work, check your HVAC filter and replace it if it’s dirty. Otherwise, call an HVAC contractor for help.
Can a dirty filter cause AC to blow warm air?
Yes, a dirty air filter can restrict airflow, causing your AC to blow warm air and work harder to cool your home.
Is it normal for AC to blow warm air sometimes?
Yes, it’s normal for your AC to blow warm air briefly when it first starts up. However, if it continues to blow warm air, you likely have an underlying issue that should be addressed by an HVAC expert.
