AC running but not cooling? What's wrong and what to check first

Five checks before you call

1. Thermostat. Mode on Cool, fan on Auto, set point below the room temperature. Replace the batteries if the screen is dim or blank.
2. Filter. If it's gray or you can't remember changing it, replace it. A choked filter starves the coil of air.
3. Breakers. Most systems have two: one for the indoor air handler and one for the outdoor unit. Reset a tripped one once. If it trips again, stop.
4. Outdoor unit. Is the fan spinning? Clear leaves, grass and anything stored within two feet of it.
5. Ice. Look at the large copper line at the outdoor unit and, if you can, at the indoor coil. Ice means turn cooling off and let it thaw (see frozen AC coil).

The common causes, easiest first

Dirty filter or blocked return

Restricted airflow is the most common cause of weak cooling and frozen coils. The fix is the filter, and making sure furniture isn't blocking the return grille.

Failed capacitor

The capacitor gives the compressor and outdoor fan motor the kick they need to start. Heat and power surges wear them out. The sign is an outdoor unit that hums but the fan doesn't spin, or an indoor fan that blows while the outdoor unit sits silent. A common, quick repair, but it's high-voltage work for a technician.

Dirty outdoor coil

The outdoor coil sheds the heat taken out of your house. Coated in grass, dust or salt, it can't, and cooling fades on the hottest afternoons. Gently rinse it from the inside out with a garden hose, with the power off, or have it cleaned at a tune-up.

Clogged condensate drain

Most systems have a float switch that shuts cooling off when the drain backs up. If the AC stopped suddenly and there's water in the pan under the air handler, this is likely. See AC leaking water.

Low refrigerant

Refrigerant isn't consumed. If it's low, there's a leak. Signs: ice on the copper line, a hiss near the indoor unit, air that's cool but not cold. The right repair is to find and fix the leak, then charge the system. Topping it up every summer just pays for the same leak again. Only EPA 608-certified technicians may handle refrigerant (EPA Section 608).

Compressor or fan motor failure

Less common, and more serious. On an older system, especially one on R-22, this is where we'd talk honestly about repair versus replacement.

When to call

Call if the checks didn't fix it within half an hour, if a breaker trips twice, if you see ice, or if the system is running but the air from the vents is barely cooler than the room. Tell us the model number from the outdoor unit's label if you can see it. We diagnose, give you a flat written price, and only fix it once you approve.