AC not cooling? Check these first
AC running but the air isn't cold? Start with what you can check yourself: the thermostat settings, the air filter, the breakers and the outdoor unit. A clogged filter or a dirty outdoor coil can make a working system seem broken. If those all check out, it's time for a technician. It's worth ten minutes of checking before you book a visit, since a lot of summer service calls end with a technician swapping a filter or flipping a breaker.
How central air works
Central air works by pulling heat out of your house and dumping it outside. The indoor part cools the air, and the outdoor unit, called the condenser, releases the heat through a big grid of metal fins while a fan blows across them. If air can't move through the filter inside, or through the fins outside, the whole system struggles. That's why the first fixes are all about airflow.
One warning sign to know: if you see ice on the copper lines or the indoor unit, turn the cooling off and let it thaw. Running a frozen system can damage the compressor, the most expensive part.
Why it isn't cooling
The first thing to check. Without enough airflow, the indoor coil can even freeze over.
Fan set to ON instead of AUTO blows room-temperature air between cooling cycles, which feels like the AC isn't working.
Dust, grass clippings and cottonwood fluff block the fins, so the unit can't get rid of heat.
A bad capacitor, a stopped fan, or a refrigerant leak needs a licensed technician.
| What you notice | Most likely | Try this |
|---|---|---|
| Nothing runs at all | Thermostat or power | Check the thermostat, breakers and outdoor disconnect. |
| Indoor fan runs, outdoor unit silent | Outdoor power or a failed part | Check and breaker. If they're on, call. |
| Both run, air isn't cold | Dirty filter or coils | Replace the filter, clean the outdoor unit. |
| Ice on the copper lines | Airflow or refrigerant | Turn it off to thaw, change the filter, then call if it returns. |
| Water around the indoor unit | Clogged | Shut it off and clear the drain line. |
Run through the checks
- Check the thermostatSet it to COOL, fan on AUTO, and a temperature at least 3 degrees below the room. Replace the batteries if the screen is dim or blank.
- Replace the air filterA clogged filter starves the system of air and can freeze the indoor coil. If yours is gray, swap it now.
- Check the breakers and the outdoor switchLook for a tripped breaker labeled AC or condenser, and make sure the disconnect box on the wall by the outdoor unit is on.
- Clean the outdoor unitTurn the power off at the disconnect. Clear leaves and weeds 2 feet back, then gently hose the fins from the outside in. Never use a pressure washer, which flattens the fins.
- Give it time and check the airTurn the power back on, wait 5 minutes, and run it for 30 minutes. Air from the vents should feel about 15 to 20 degrees cooler than room air.
Watch it done
- The thermostat is on COOL and the system starts
- The outdoor unit runs with its fan spinning
- After 30 minutes, vent air feels about 15 to 20 degrees cooler than the room
Outdoor unit hums but fan won't spin? Turn it off and call a technician.
If the house is still warm
If the outdoor unit hums but its fan isn't spinning, turn the power off right away. That's usually a failed capacitor, a quick repair for a technician, but running it that way can damage the compressor.
If the indoor unit runs but the outdoor unit is silent, check the outdoor disconnect and breaker again, and look at the thermostat wiring for anything chewed or loose.
What a pro typically charges (a rough estimate; prices vary by area): A typical AC service call runs $100–$300. A capacitor replacement usually costs $150–$400; refrigerant leak repairs can run $300–$1,500.
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