Why Isn't My AC Cooling the House?

Why isn't my AC cooling the house?

If your AC is running but the house won't cool, the most common culprits are a clogged air filter, low refrigerant from a leak, a dirty outdoor condenser coil, a frozen evaporator coil, or a thermostat problem. A few you can check yourself in five minutes, the rest need a licensed technician.

Reviewed by Matthew Palmieri, President Updated June 15, 2026

Interactive diagram

AC running but not cooling? Check these five, in order

Steps 1–4 are safe to check yourself. Step 5 means turn it off and call.

Cooled air (when everything works)Warm return air

Tap or click a numbered marker to see what each part does, or watch the animated flow to follow the cycle.

Start here: 5-minute checks you can do

Thermostat: set to Cool, and a few degrees below the room temperature. Try fresh batteries.
Air filter: a dirty filter chokes airflow and is the single most common cause. Replace it if it looks gray.
Breakers: the indoor and outdoor units often have separate breakers, reset any that tripped.
Vents & registers: make sure supply and return vents are open and unblocked.
Outdoor unit: confirm the fan is spinning and clear leaves, grass, and debris from around it.

Common causes that need a pro

Low refrigerant from a leak, the system can't absorb heat properly. Requires leak repair + recharge by an EPA-certified tech.
Frozen evaporator coil, caused by airflow or refrigerant problems; ice blocks cooling entirely.
Dirty condenser coil outside, traps heat and kills efficiency.
Failed capacitor or contactor, the compressor or fan won't start.
An aging or undersized system that simply can't keep up in a Missouri heat wave.

When it's an emergency

Call right away if you have no cooling during a heat advisory (especially with seniors, infants, or pets at home), smell something burning, or see ice on the refrigerant lines. We answer 24/7.

Preventing it next time

Most mid-summer breakdowns trace back to skipped maintenance. A spring tune-up cleans the coils, checks refrigerant, and tightens electrical connections before the heat hits, our USA Savings Club members get priority scheduling for exactly this reason. If a system keeps failing, our repair-or-replace guide can help you decide whether another fix is worth it.

Frequently asked

Why is my AC running but blowing warm air?

The most common reasons are a thermostat set to the wrong mode, a clogged filter restricting airflow, a tripped breaker on the outdoor unit, low refrigerant from a leak, or a frozen evaporator coil. Check the filter, thermostat, and breakers first; if those are fine, it's time for a technician.

Why does my AC keep freezing up?

Ice on the indoor coil or refrigerant lines usually means restricted airflow (dirty filter or blocked vents) or low refrigerant. Turn the system off so the ice can melt, replace the filter, and call for service, running a frozen system can damage the compressor.

Can I add refrigerant to my AC myself?

No. Low refrigerant means there's a leak, and adding more without finding it just wastes money and harms the environment. Refrigerant handling is federally regulated and requires EPA certification, a licensed technician should find and fix the leak, then recharge the system.