AC running but not cooling? An Austin homeowner's checklist

First: what's normal in an Austin summer

Normal daily highs in Austin sit above 90° from late May to late September, and July and August average around 97°. A home AC is designed to cool roughly 15 to 20 degrees below the outdoor temperature. So at 104° outside, a house holding 78° to 80° in late afternoon may be doing its job, especially upstairs or in west-facing rooms.

What's not normal: the house is warmer than it was at noon and still climbing, the air from the vents feels the same as the room, or the system runs nonstop into the night and never catches up once the sun goes down.

Measure it: the temperature split

Put a kitchen thermometer in a supply vent near the indoor unit, then in the return grille, after the system has run 15 minutes. A healthy AC usually shows a 15 to 20 degree difference. Much less than that points to a refrigerant, compressor or airflow problem, and that's a call for a tech.

Five things to check yourself

These fix a surprising number of calls, and they're all safe to do.

• Thermostat: set to Cool, fan on Auto, a few degrees below room temperature, fresh batteries.
• Filter: if it's gray and matted, replace it. A clogged filter can freeze the coil.
• Breakers: check both the indoor unit and the outdoor (condenser) breaker. Reset a tripped one once. If it trips again, stop.
• Outdoor unit: is the big fan on top spinning? Clear grass, leaves and anything within two feet of the coil.
• Drain safety switch: many attic units have a float switch that kills the AC when the drain pan fills. Water in the pan means a clogged drain line.

Signs you need a technician

Call if you see ice on the copper lines or indoor coil (turn cooling off, run fan only, let it thaw), the outdoor fan isn't spinning while the unit hums, you hear buzzing or clicking without startup, or breakers keep tripping. Capacitor and contactor failures are the most common Austin-summer culprits, and they're quick fixes.

Help it keep up on the hottest days

Close blinds on west and south windows by early afternoon, avoid the oven and dryer between 3 and 7 pm, and don't crank the thermostat way down. Setting 65° doesn't cool faster, it just makes the system run longer. Pre-cooling the house in the late morning helps it coast through peak heat.