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Troubleshooting Guide · The Honest Answer First
Why does my AC run constantly?
Here’s the part most HVAC websites won’t lead with: in a Southwest Florida summer, your AC might be running constantly because it’s working exactly right. Sometimes it really is a problem. This guide shows you how to tell the difference before you pay anyone a dime.
Real person answers 24/7 · Naples, Cape Coral & Fort Myers
The Florida truth: constant running is often normal here
An air conditioner is sized to keep your house about 20° cooler than the air outside on a design-day afternoon. In July and August in Collier and Lee County, that design day shows up daily: mid-90s, heat index pushing 105, humidity the machine has to wring out of the air on top of the heat. To hold 75° inside against that, a correctly sized system has to run at or near full capacity — which means long cycles, sometimes nearly continuous, from early afternoon into the evening.
That’s not a defect. That’s the machine matched to the load. A system with huge spare capacity in August would be badly oversized for the other ten months, and oversized systems cause their own expensive problems (more on that paradox below).
So before you assume something’s broken, check what actually matters:
- Is the house holding the setpoint? Thermostat set to 75, house at 75 or 76 on a 95° afternoon, long runtimes — that’s a healthy Florida system doing a hard job.
- Does it cycle off at night? When the outdoor temp drops to the high 70s after dark, a healthy system gets breaks. Runtime should ease off noticeably.
- Is the air at the vents genuinely cold? Cold supply air plus a house that keeps up means the constant running is effort, not failure.
If you answered yes to those three, you can probably stop reading and go enjoy the lanai. Constant doesn’t mean broken. It means August.
Now the other half of the honest answer
When constant running IS a problem
The runtime itself isn’t the symptom. These are the symptoms:
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Still running flat-out at night — it’s 78° outside at 11pm and the system never cycles off. The easy overnight load should give it breaks.
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The house never reaches setpoint — thermostat says 75, house sits at 79 all afternoon and never closes the gap.
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Your FPL bill jumped — compare against the same month last year, not last month. Same weather, meaningfully higher bill: the system is burning extra hours to do the same job.
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Weak airflow or ice — vents barely breathing, or frost on the refrigerant lines. That’s a system running constantly because it physically can’t move enough cooling. See our frozen AC guide.
One or more of those alongside the constant running? Keep reading. The causes below are ranked in the order we actually find them.
Ranked by how often we actually find them
The real causes of a nonstop AC
1. Dirty filter or coil
The most common and cheapest cause. A clogged filter or grime-caked coil chokes airflow, so each hour of runtime delivers less cooling and the system compensates with more hours. Florida filters clog in 4–6 weeks, not the 90 days on the package.
2. Refrigerant leak
Low charge means the system moves less heat per hour, so it runs more hours and still loses ground. Salt air eats SWFL coil copper, so leaks are common here. This one needs gauges, a licensed tech, and a real leak repair — not a seasonal top-off.
3. Leaky ducts
The sneaky one. Supply ducts run through a 130° attic; if they leak, you’re paying to cool the attic while the thermostat waits for air that never fully arrives. Sealed, clean ducts fix runtime and air quality at once — see our duct cleaning service.
4. Failing compressor
A worn compressor pumps less refrigerant than it should, so the system limps along at partial capacity, running forever to deliver half the cooling. Usually shows up with rising amp draw and a rising bill on a 10-to-15-year-old unit.
5. Undersized system
If the system has never kept up on hot afternoons — even when new, even freshly serviced — it may simply be too small for the house. Common after additions, enclosed lanais, or a lowball install that skipped the load calculation.
6. Thermostat in a sun patch
A thermostat that catches afternoon sun through a window, or sits near a hot kitchen, reads the room hotter than the house really is — and drives the system nonstop to cool a hot spot. A two-foot relocation has ended more than one “broken AC” call.
One more quiet contributor: a thin attic. Florida attics hit 130°+ and radiate heat down through skimpy insulation all evening, adding load your AC has to fight hour after hour. If your system runs hard and the ceiling feels warm at 9pm, blown-in insulation is often the cheapest runtime fix on this whole list.
The paradox: a constantly running right-sized AC beats an oversized one
Here’s where a commission-driven company sees an opening: “It runs all the time? You need a bigger unit.” Please don’t buy that without the math.
An oversized system blasts the air to temperature in 10 minutes and shuts off. Sounds great — except cooling the air is only half the job in Florida. The other half is dehumidifying, and that only happens while the system runs and the coil stays cold. Short cycles pull the temperature down and leave the moisture behind. You get a house that’s 74° and clammy, sweating windows, musty closets, and a system beating itself to death with constant starts. We wrote a whole guide on that exact misery: why your house is humid with the AC running.
A right-sized system running long, steady cycles on a 95° afternoon is doing both jobs: temperature and humidity. Long runtimes with the house comfortable and dry are the sign of a good install, not a sales opportunity. Bigger is not better in SWFL. Correct is better.
Ten minutes, zero dollars
Quick self-checks before you call anyone
1
Filter test
Pull the filter and hold it up to a light. Can’t see through it? Replace it, give the system a day, and see if runtime eases. This alone resolves a surprising share of these calls.
2
Vent test
Feel the air at a supply vent. It should be genuinely cold — roughly 18–20° cooler than the room. Cool-ish or weak airflow points at the filter, coil, ducts, or refrigerant.
3
Night test
After 10pm, watch the outdoor unit. It should cycle off for stretches once outdoor temps fall to the high 70s. Nonstop overnight running is a real symptom, not August.
4
Bill test
Open your FPL account and compare this month against the same month last year. Similar weather, a bill that’s jumped, and longer runtimes — the system is losing efficiency somewhere.
Also worth a glance: ice or frost anywhere on the copper lines. If you see it, stop and read our frozen AC guide before running the system any further — running frozen is how compressors die.
What constant running does to your FPL bill
Honest numbers logic, no scare tactics. A typical 3-ton residential system draws roughly 3 to 3.5 kilowatts with the blower running. At FPL residential rates of around 15 cents per kilowatt-hour, that’s about 45 to 50 cents for every hour it runs.
Now the math that matters. In August, a healthy system might run 12–14 hours a day — call it roughly $6 a day, $180 a month for cooling. That’s normal Florida summer money, and no repair changes it much. But a system limping on a dirty coil, a low charge, or leaky attic ducts can burn 4 or more extra hours a day to hold the same temperature. Four extra hours at 50 cents is $2 a day — about $60 a month, every month, for nothing. Over a cooling season that’s several hundred dollars quietly leaving through a problem that’s often a modest one-time repair.
That’s why the bill test above compares year over year. The weather sets the baseline. The gap above the baseline is the problem — and it’s usually cheaper to fix than to keep paying for.
Failed a self-check, or just want a straight answer? Diagnosis first, written flat-rate quote second, your decision always. If the system’s fine, we’ll tell you it’s fine.
☎ Call (239) 977-2010 — Get the Honest Read
Or text your runtime question to the same number
Runtime questions, straight answers
Constantly running AC FAQs
Is it bad for my AC to run all day?
Not in a Florida summer. Compressors are happiest running long, steady cycles — starts and stops cause more wear than runtime does. A system holding setpoint through long afternoon cycles, then getting breaks overnight, is operating the way it was designed to.
How many hours a day should an AC run in Southwest Florida?
There’s no magic number, because it tracks the weather. On a 95° August afternoon, near-continuous running from midday into the evening is normal for a right-sized system. The healthy pattern is long daytime cycles with clear off-cycles overnight. The unhealthy pattern is nonstop running around the clock regardless of outdoor temperature.
Why does my AC run constantly but never cool the house?
Runtime without results means capacity is leaking away somewhere: restricted airflow from a dirty filter or coil, low refrigerant, duct leaks dumping cool air into the attic, or a compressor that’s wearing out. Do the ten-minute self-checks above; if the filter and vents check out, the rest takes a licensed tech with gauges. That’s a standard AC repair diagnosis, same-day across Collier and Lee County.
Will a constantly running AC raise my electric bill?
Runtime is exactly what you pay FPL for — roughly 45 to 50 cents per hour for a typical 3-ton system. Normal August runtime is normal August money. The red flag is a bill meaningfully higher than the same month last year, which means the system is burning extra hours to do the same job. Those extra hours can add $60 or more a month.
Should I buy a bigger AC so it doesn’t run all the time?
Almost never, and be wary of anyone who suggests it without a load calculation. An oversized system short-cycles: it cools the air fast and shuts off before it dehumidifies, leaving you with a cold, clammy, musty house and a compressor worn out by constant starts. In Florida, the right size runs longer and does the job better. Our guide on humidity with the AC running covers what oversizing does to a house.
How do I reduce my AC’s runtime without touching the equipment?
Cut the load it fights. Twice-a-year professional maintenance keeps the coil and charge at full capacity, fresh filters every 4–6 weeks keep airflow up, and topping up thin attic insulation blocks the 130° attic from radiating heat into the house all evening. Closing blinds on west-facing windows during the afternoon helps more than most gadgets.
Fine or failing — know for sure
Get a straight answer on your system
Maybe it’s August. Maybe it’s a $30 filter, a duct leak, or a compressor on its way out. We diagnose it honestly and put the price in writing before any work — and if the system is fine, that’s exactly what we’ll tell you. See how a visit runs on our AC repair page, or reach out now:
- Fastest: call (239) 977-2010 — 24/7 live answer
- Easiest: text your question or a photo to the same number
- Form: tell us the symptoms, we call you back
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