Why Is My AC Not Cooling? 8 Common Causes (and When a Warranty Pays)

The short version: when an AC runs but won't cool, the cause is usually one of eight things — and a few you can check yourself in five minutes. For the rest, a home warranty with air-conditioning coverage pays to repair or replace the failed part, up to your plan's terms.

First, the 2-minute checks

Before you call anyone, rule out the easy stuff:

Thermostat set to Cool and below room temperature?
Air filter clean? A clogged filter is the number-one cause of weak cooling.
Breaker tripped for the AC or furnace circuit?
Outdoor unit running and clear of leaves and debris?

A dirty filter or tripped breaker fixes a surprising share of AC-not-cooling calls for free.

8 common causes an AC isn't cooling

Dirty air filter — restricts airflow; swap it and give it an hour.
Low refrigerant or a leak — cools weakly, may ice up; needs a technician.
Frozen evaporator coil — turn the system off and let it thaw.
Failed capacitor — the compressor or fan won't start; a common, inexpensive part.
Bad compressor — the heart of the system; the costliest failure.
Dirty condenser coil — the outdoor unit can't dump heat.
Failed blower motor — little or no air at the vents.
Faulty thermostat — sends the wrong signal, or none at all.

When a home warranty covers it

Causes 2 and 4–7 are mechanical failures from normal wear and tear — exactly what a home warranty is for. If your plan includes air conditioning (usually a Total Plan or add-on), you file a claim, a licensed HVAC technician is dispatched, you pay one flat service fee, and your plan covers the covered repair — or replaces the unit when it can't be fixed, up to the plan's terms.

What a warranty won't cover: a problem that existed before your coverage started, or damage from skipped maintenance (like a coil that failed from a filter nobody changed). See our full HVAC & AC coverage page for the details.

Key takeaways

Check the thermostat, filter, breaker, and outdoor unit first — these fix many not-cooling cases for free.
The costly causes — compressor, capacitor, blower, refrigerant leak — are mechanical failures a home warranty with AC coverage pays for.
You pay one flat service fee; the plan covers the covered repair up to its terms.
Pre-existing problems and neglect aren't covered.

Worried your AC could go in the next heat wave? Get a free, no-obligation quote and we'll match you with a plan that covers it.

Frequently asked questions

Will a home warranty cover a bad AC compressor? Yes, if your plan includes air-conditioning coverage and the compressor failed from normal wear and tear. The plan repairs or replaces it up to your plan's terms, and you pay the service fee.

Why is my AC running but not blowing cold air? The most common causes are a dirty filter, low refrigerant, a frozen coil, or a failed capacitor. Check the filter and thermostat first; the rest need a technician.