Let’s start with the easy things to troubleshoot

Thermostat setting

The first thing you should do it is check your thermostat. Make sure your system is set to “COOL,” your fan is switched to “AUTO” and your temperature setting is well below what the room temperature reads on your thermostat (at least 5 degrees).

Dirty condenser unit

Take a look at your outside unit—also known as a “condenser unit”. Make sure there’s nothing visibly interfering with your system’s moving parts. Look for dirt, leaves, tall grass or debris. If you see a blockage, remove it (and remember the importance of regular air conditioning maintenance).

Dirty air filter

When was the last time you changed your air filter? It isn’t an urban myth; a clean air filter is very important.

Why? The air filter protects your AC’s inner workings from dust, dirt and debris and promotes proper airflow. For hot weather climates, you should check your air filter once a month.

Here’s some help identifying more complex causes

Low refrigerant leak

Low refrigerant is another common reason for an AC to blow warm air. Losing refrigerant means losing your cool. However, you’ll need a professional to figure out if this is the problem. Remember, refrigerant isn’t used up like gas. So if you’re low it means you have a leak and a professional needs to find and fix the leak before adding more refrigerant.

Leaky air ducts

It’s also possible you have a leak in an air duct that’s messing with your system’s cooling process. If your ducts are hidden in your walls, attic, or basement, you’ll need to contact a professional for help.