Why Is My AC Blowing Warm Air? 

We know it’s frustrating to feel warm air coming from your AC on a hot and humid day. But don’t worry, we’re here to help you with explanations on why your AC may be blowing warm air.

If your AC is blowing warm air, it’s likely because of 1 of these 5 problems:

• Incorrect thermostat settings

• A dirty air filter

• A dirty evaporator coil

• Low refrigerant levels

• A faulty compressor

We’ll go into more detail about each of these problems to help you determine why your AC is blowing warm air.

Want a professional to repair your AC? Our technicians at Aiello are ready to help!

If your AC is blowing warm air, the first thing you should check is the thermostat and make sure it is set to COOL mode.

We know—this may sound obvious, but sometimes the thermostat accidentally gets switched to HEAT mode or some homeowners forget to switch the thermostat from HEAT to COOL as the seasons change. Both (very common) mistakes would explain why you’re feeling warm air coming from the vents.

You’ll also want to make sure the fan setting on the thermostat is set to AUTO instead of ON. If the thermostat is set to ON, the blower will push air into your home non-stop—even when the AC isn’t actively cooling any air. This could explain why you’re feeling warmer air coming out of the vents sometimes.

Conversely, setting the thermostat to AUTO will ensure that your AC blower fan only blows air during cooling cycles, which means it will only ever push cold air into your home.

Solution: Check that the thermostat is set to COOL, and that the dan is set to AUTO.

The next thing you’ll want to check is the air filter.

A dirty air filter prevents air from flowing into your AC to be cooled, which decreases the amount of cool air being blown throughout the home. While a dirty filter might not directly cause warm air, it will hinder your AC’s performance considerably.

A dirty air filter also leads to other issues such as:

• Higher energy bills
• Extra wear and tear on AC components
• Overheated AC parts, which cause the system to shut down

Solution: Check your air filter. If it is dirty, replace it with a new one. In the future, be sure to replace your air filter at least once every two months.

First, a quick explanation about what the evaporator coil is.

The evaporator coil is the part that actually cools your home’s air and is located in the indoor unit (see below). The evaporator coil contains refrigerant, which is a cold liquid substance that absorbs heat from air that passes over the coils, which is how your home’s air is cooled.

Here’s the problem: Dust and debris can settle on the evaporator coil. This debris prevents the refrigerant from absorbing as much heat, which makes the air coming out of your vents feel warmer than normal.

Solution: You should contact an HVAC professional to inspect your evaporator coil and clean it if it is dirty.

Above, we mentioned that refrigerant is the substance that removes heat from your home’s air.

That said, if your AC is low on refrigerant, the system cannot remove as much heat from your home’s air, which will make the air coming out of your vents feel warmer.

So how does an AC lose refrigerant?

The only way to have low refrigerant levels is if there is a leak somewhere in the system. Unlike gas in a car, refrigerant should never get “used up” during the lifespan of an AC. Instead, in normal operation, refrigerant cycles in a closed-loop throughout your AC system.

If you have a refrigerant leak, you may also notice signs such as:

• Ice on the refrigerant line or evaporator coil
• Bubbling or hissing sound coming from the AC
• A chemical smell
• Higher-than-normal energy bills

Solution: Contact an HVAC professional for help. A professional can find the source of the leak, repair it and then recharge the AC with the appropriate amount of refrigerant.

The compressor is the part of your air conditioner that circulates refrigerant throughout your AC system.

If the compressor is starting to go bad (which can happen as the AC ages), your air conditioner will struggle to cool your home, resulting in warmer air coming out of the vents.

Besides warm air coming from your vents, the following signs also point to a failing compressor:

• The AC keeps tripping the circuit breaker
• The outdoor unit makes loud noises
• The outdoor unit vibrates when the AC first turns on
• The airflow coming out of the vents is weaker

Solution: An HVAC professional will need to inspect the compressor and make sure it’s working properly. If the compressor is bad or on its last leg, it will need to be replaced. Because the compressor is such an expensive part, it may be better to purchase a new AC altogether rather than replace only the compressor.

The professional you hire will help you determine whether it’s best to replace the compressor or buy a new AC.