AC Blowing Warm Air? 7 Causes (And When to Call)

The most common summer call we get: “It’s running, but the air isn’t cold.” Here are the seven usual causes — three you can check yourself in five minutes, and four that mean it’s time to call.

Check these first (free, five minutes)

1. Thermostat settings. Genuinely the cause more often than anyone admits. Confirm it’s set to COOL (not HEAT or FAN), the setpoint is below room temperature, and — if it takes batteries — swap them.

2. The air filter. A filter choked with a Midlands spring’s worth of pollen and dust strangles airflow and can freeze the evaporator coil solid. If it’s gray and furry, replace it, then give the system an hour.

3. The breaker and disconnect. Find your electrical panel and check for a tripped AC breaker; check the outdoor disconnect box by the condenser too. A breaker that trips again immediately is telling you something — stop resetting it and call.

These mean call a pro

4. Frozen evaporator coil. Ice on the refrigerant lines or the indoor unit means airflow or refrigerant trouble. Turn the system OFF (fan can stay ON to thaw it) — running a frozen system can kill the compressor.

5. Refrigerant leak. Hissing, oily residue on fittings, or gradually weakening cooling over weeks. Refrigerant doesn’t wear out; if it’s low, it leaked, and topping off without finding the leak is money down a drain.

6. Failed capacitor or compressor. The outdoor unit hums but the fan doesn’t spin, or it clicks and gives up every few minutes. Capacitors are cheap ($150–$350); compressors are not. Diagnosis tells you which.

7. Duct failures. Some rooms cold, others warm, and weak airflow everywhere? In older Columbia homes, disconnected or collapsed attic ductwork is a frequent culprit — your cold air is cooling the attic.

One hard rule: if you see ice, turn the system off. Every minute a frozen system runs is a coin flip on a $2,000 compressor.

When in doubt

If the five-minute checks don’t solve it, you’re in “call a pro” territory — and in a Columbia summer, sooner beats later. A capacitor caught today is a cheap fix; the compressor it takes down next week is not.