If your air conditioner is running and the house is still sitting at 80 degrees, the whole system usually hasn't failed at once. Something specific is stopping it from cooling: airflow, drainage, power to one half of the system, or refrigerant. A few of those you can check yourself in ten minutes with no tools. The rest need gauges and a license. Here is how we tell them apart.
It matters more here than in most places. From May through October in Sarasota and Manatee County, a system that stops cooling at 2pm can let a house climb into the high 80s by evening, and the humidity climbs with it. Check the easy things first, but know when to stop.
What “running but not cooling” usually means
A central air conditioner has two halves. The air handler inside blows air across a cold coil. The condenser outside gets rid of the heat that coil picked up. If you can hear the indoor blower and feel air at the vents, the inside half is working. That is usually what people mean when they say the A/C is running.
When the air from the vents is close to room temperature, the usual causes are a dirty filter that has let the indoor coil freeze, a thermostat that isn't actually calling for cooling, an outdoor unit that has lost power, a clogged condensate drain that has shut the system down through its float switch, or low refrigerant from a leak.
A quick test: hold your hand, or a kitchen thermometer, at a supply vent, then at the return grille. In a healthy system the supply air is roughly 15 to 20 degrees cooler than the air going into the return. If the difference is only a few degrees, the cooling side isn't doing its job. If the air is cold but barely moving, you have an airflow problem instead.
1. Check the air filter
More no-cool calls trace back to the filter than to anything else. A clogged filter starves the indoor coil of air, the coil gets colder than it should, the moisture on it freezes, and once there is ice on the coil almost no air gets through. The blower keeps running, so the system sounds normal.
Pull the filter out and hold it up to a light. If you can't see light through it, replace it. Between spring pollen, lovebug season, construction dust in newer neighborhoods and pets indoors all year, a standard one-inch filter here often needs changing every month through the summer, not every three months as the package says.
If you find ice on the copper lines or the indoor coil, set the thermostat to OFF and the fan to ON. That moves air across the coil without cooling it and melts the ice. It can take a few hours, so put a towel down, because that water has to go somewhere. Once it has thawed and a clean filter is in, run the system again. If it freezes a second time, turn it off and call. Repeated freezing almost always means low refrigerant or a blower problem, and running it that way can damage the compressor.
2. Check the thermostat
It sounds obvious, and it still trips people up. Make sure the thermostat is set to COOL, not HEAT, and not AUTO stuck in the wrong mode. Set the fan to AUTO, not ON. With the fan on ON, the blower runs nonstop, so you feel air at the vents between cooling cycles and it seems as if the system is running but not cooling. It also blows moisture off the coil back into the house, which makes the rooms feel clammy.
Set the temperature four or five degrees below the room temperature and listen for the outdoor unit to start. Many thermostats deliberately wait a few minutes before restarting the compressor, so give it five. If the screen is dim, blank or acting strangely, replace the batteries. A thermostat with weak batteries can keep its display lit and still fail to start the outdoor unit.
If the power has flickered, a WiFi thermostat may have come back on a schedule or a hold you didn't set. Check the schedule before assuming the equipment has failed.
3. Check the breakers
Most homes have two breakers for the A/C, one for the indoor air handler and one for the outdoor condenser, plus a disconnect box on the wall next to the outdoor unit. If only the outdoor breaker has tripped, you get exactly this symptom: the blower runs and nothing cools.
Reset it once. If it trips again, leave it off and call. A breaker that keeps tripping means something is drawing more current than it should, and resetting it over and over can turn a small repair into a big one.
4. Look at the outdoor unit
Stand next to the condenser while the thermostat is calling for cooling. You should hear the compressor running and see the fan on top spinning, with warm air blowing up out of it. If the unit hums but the fan isn't turning, or the fan spins but the air coming off it isn't warm, the problem is electrical or mechanical and it needs a technician. A failed capacitor is one of the most common causes, and it isn't a part to handle yourself, because it can hold a charge even with the power off.
Clear anything crowding the coil. Shrubs, vines, mulch piled against the base and grass clippings blown into the fins all cut the airflow the unit needs. Two feet of clear space on every side is a good target. With the power off at the disconnect, you can rinse the outside of the coil gently with a garden hose. Don't use a pressure washer, because the fins bend easily.
Ice on the larger copper line at the outdoor unit points back to the same freeze problem as inside: airflow or refrigerant.
5. Check the condensate drain and float switch
In our humidity, an indoor coil pulls gallons of water out of the air every day. That water runs out through a PVC drain line, which usually ends at a short pipe outside near the air handler or the foundation. Algae grows in that line, and when it blocks, the drain pan fills.
Most systems have a float switch on the pan or the drain line to stop the pan overflowing into your ceiling or hallway. When the water rises, it shuts the cooling off. Depending on how it is wired, the blower may keep running, which looks exactly like an A/C that runs but doesn't cool. If the system stopped cooling during a humid stretch with no warning noises, look for standing water in the pan or around the air handler.
Clearing a blocked line properly means vacuuming it out from the outside end, flushing it, and finding out why it blocked. If it keeps happening, it is often tied to duct and humidity problems in the rest of the house. Our ductwork and air quality page covers that side of it.
When to stop and call
Call a technician when:
- the filter is clean and the system still won't cool
- the coil freezes a second time
- a breaker trips twice
- the outdoor fan won't turn, or the unit hums without starting
- you smell burning or anything electrical
- water is coming out somewhere it shouldn't
Refrigerant is never a homeowner job. Handling it requires EPA certification, and a low charge means there is a leak that needs to be found, not just topped up.
We provide emergency service 24 hours a day, 7 days a week, so a failure at midnight in August doesn't have to wait until morning. When you call, tell us what the thermostat says, roughly how old the system is and what you've already checked. It speeds up the diagnosis.
Most of the causes above are preventable. A clean coil, a flushed drain line and a tested capacitor before summer starts are the difference between a system that coasts through the season and one that quits in the heat. That is what our A/C maintenance visits are built around.
If you've worked through these checks and the house still won't cool, our A/C repair team will come and find the problem.
Still not cooling?
We answer the phone 24/7, including nights, weekends and holidays. Upfront pricing before any work starts.