Why Is My AC Blowing Hot Air?

Worried about the warm air you feel coming from your vents? We’ll explain what problems cause your AC to blow hot air and how to fix them.

The most common problems that cause an air conditioner to blow hot air are:

• A dirty evaporator coil
• A refrigerant leak
• A malfunctioning outdoor unit

We’ll go into more detail about each of these problems below. But first, let’s look at a few things you should do before you call a professional.

The first thing you’ll want to do is make sure your thermostat is set to COOL and not HEAT. It may sound obvious, but sometimes the COOL setting accidentally gets switched to HEAT, which would explain why you’re feeling warm air.

While you’re at your thermostat, make sure the fan is set to AUTO instead of ON. If your thermostat is set to ON, the indoor AC fan will run non-stop—even when your air conditioner isn’t cooling any air. This means when the AC cooling cycle is off, the fan will still be working, pushing warm air through the vents. If you only feel warm air occasionally, this could be the problem.

On the other hand, when the AUTO fan setting is selected, the fan will only push air into your home during cooling cycles, which will ensure the air coming out of your vents is always cold.

Next, you should check your air filter to make sure it is clean. If your filter is dirty (like the one shown in the image below), replace it with a new one.

While a dirty air filter doesn’t directly cause hot air to come out of your vents, it hinders the performance of your air conditioner and can cause the system to struggle to reach your desired temperature.

After you change your dirty air filter, let your AC run for at least 30 minutes. If the warm-air problem persists, you’ll need to contact a professional to troubleshoot the problem.

Now let’s look at other possible problems that could explain why your AC is blowing hot air.

The evaporator coil is tucked inside the indoor AC unit and is the part that’s responsible for cooling your home’s air.

Inside the evaporator coil, a liquid substance called refrigerant absorbs heat from warm air that blows over the coil. However, if the evaporator coil is covered in dirt, then the refrigerant can’t absorb as much heat from the air, which means the air coming out of your vents will feel warmer.

Dirt buildup on the evaporator coil is very common—especially if your AC has not been maintained regularly by a professional. If your evaporator coil is very dirty, you may also notice a musty smell caused by mold buildup.

A trained HVAC professional can inspect your evaporator coil and clean it. We don’t recommend that you attempt to clean the evaporator coil yourself because the coils can be easily damaged if not handled properly.

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

Because refrigerant is essential to the cooling process, if your AC is low on refrigerant, your AC will struggle to cool your home’s air and you may feel warm air coming from the vents.

Here’s the thing: Almost always, if your AC is low on refrigerant, it means there’s a leak somewhere in your AC system.

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

• A sweet chemical scent
• A hissing sound
• Ice on the refrigerant lines
• Pools of water around the indoor unit
• Higher utility bills than normal

A professional will need to find the source of the leak and “recharge” the AC to make sure it has the correct amount of refrigerant.

Refrigerant can cause serious health issues if handled incorrectly, which is why we recommend having a certified professional repair any refrigerant-related problems.

The outdoor unit is responsible for dispersing the heat absorbed by refrigerant into the outside air. This allows the refrigerant to cool down and go back to the indoor unit to absorb more heat, continuing the cooling cycle.

However, if components in the outdoor unit are malfunctioning, your AC can’t disperse heat outside. This prevents the refrigerant from cooling down to the appropriate temperature, which results in your AC blowing warmer air than it should.

Components in the outdoor unit that commonly malfunction include:

• The compressor, which pumps refrigerant throughout the AC system
• The condenser coil, where heat is removed from refrigerant.
• The fins surrounding the outdoor unit, which help dissipate heat into the outdoor air.

If any of these components are malfunctioning, a professional will need to repair or replace the broken part.