Why Is My AC Not Cooling?

Before assuming the worst, know this: the cheapest cause is also the most common. Work through these in order and you will either solve it yourself or walk into the contractor conversation knowing far more than most callers.

1. A Clogged Air Filter

A filter packed with dust chokes airflow across the indoor coil. The system runs longer, cools less, and can eventually freeze the coil solid. Pull the filter and hold it up to a light: if you cannot see light through it, replace it and give the system a few hours. This single check resolves a surprising share of "AC not cooling" calls.

2. A Dirty Outdoor Unit

The condenser outside dumps your home's heat into the air. When its fins are matted with cottonwood, grass clippings, and dust, that heat has nowhere to go. With the power off, you can gently rinse loose debris from the outside of the unit. Anything deeper belongs to a professional.

3. Thermostat Problems

It sounds obvious, but confirm the thermostat is set to cool, below room temperature, and has working batteries. A misreading or miscalibrated thermostat can imitate a dead system.

4. A Tripped Breaker or Failed Capacitor

If the indoor blower runs but the outdoor unit is silent, check the breaker panel. A breaker that trips once can be reset once; a breaker that trips again means a fault that needs diagnosis. A failed capacitor, the small component that starts the compressor and fan, shows the same symptom and is a routine professional repair.

5. Low Refrigerant

Refrigerant does not get used up; if it is low, it leaked. Symptoms include warm air, ice on the copper lines, and hissing sounds. Topping off without finding the leak is money spent twice. Refrigerant handling is licensed work, full stop.

6. A Failing Compressor

The compressor is the heart of the system and the most expensive component. Hard starting, loud operation, or an outdoor unit that hums but never quite starts can point here. On an older system, this diagnosis often triggers the repair vs. replacement conversation.

When to Call

Call after the filter, thermostat, and breaker checks, or immediately if you see ice on the lines (turn the system off first) or smell anything burning. Describe what you found when you tried the basics; it genuinely speeds up diagnosis. More detail lives on the AC repair page.