You set the thermostat to 70°. The AC kicks on. Air comes out — but it’s warm. Or worse: room temperature. Here’s a Florence-area technician’s guide to the most common reasons your AC is running but not cooling.
Always check this first. Thermostat set to “Heat” instead of “Cool.” Fan set to “On” instead of “Auto” — meaning the fan blows even when the AC isn’t actively cooling, so warm air comes out between cooling cycles. Set to Cool, Auto, and your desired temp.
A heavily clogged filter restricts airflow so much that the indoor evaporator coil freezes. Once it’s frozen, no cooling happens — just warm air through ice. Check your filter monthly. If it’s gray and dusty, replace it. If your AC is already frozen, turn it OFF for several hours to thaw, replace the filter, and restart.
Walk outside and look at your AC unit. Is the big fan spinning? If not, the AC isn’t cooling — it’s just blowing room-temperature air through the ducts. Common causes: tripped breaker, blown capacitor, bad contactor, or an obstruction (leaves, branches, or a critter).
Refrigerant doesn’t “get used up” — if it’s low, there’s a leak. Symptoms: AC runs constantly, ice on the refrigerant lines, hissing sounds from the unit, electric bills climbing. Don’t just “top off” the refrigerant — that’s a bandaid. The leak needs to be found and fixed.
The outdoor unit needs airflow to release heat. If the fins are caked with dirt, grass clippings, or cottonwood fluff, it can’t shed heat efficiently. Result: unit runs constantly, struggles to cool. Easy DIY: spray the outdoor coil with a garden hose (don’t use a pressure washer — bends fins).
Capacitors are small cylindrical components that give the compressor and fan motors the “kick” they need to start. They fail in heat — usually mid-July. Sign of a failed capacitor: outdoor unit hums but fan doesn’t spin, or unit clicks but doesn’t start. This is a $200–$350 repair, usually same-day.
If you’ve been running the AC hard with restricted airflow (clogged filter, blocked vents, low refrigerant), the indoor coil can freeze into a block of ice. Once frozen, it can’t absorb heat — so warm air blows out. Solution: turn off the AC for 4–6 hours to thaw. Replace the filter. Then call a tech if it freezes again — there’s a deeper issue.
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