New to Florida: nine things people get wrong about running the AC

Air conditioning in a subtropical climate is a different machine doing a different job. Up north it removes heat and the dryness is a side effect nobody notices. Here it removes heat and water, roughly in that order of visibility and the reverse order of importance, and most newcomer mistakes come from managing the first while ignoring the second.

1. Setting it to 68 to cool the house faster

An air conditioner has one speed. Setting the thermostat to 68 when you want 76 does not make it work harder; it makes it run longer, past the point you wanted, until it either reaches 68 or gives up. On a hot afternoon it may never get there, in which case it simply runs continuously.

Set the temperature you want. If the house is not reaching it, that is information about the equipment or the building, and lowering the setpoint hides the information without solving anything.

2. Leaving the fan on ON

This is the most consequential setting in the house and the one people change without thinking. On AUTO, the blower runs only while the system is cooling. On ON, it runs continuously.

The problem is what happens between cooling cycles. The evaporator coil is wet, because that water is the humidity it just pulled out of the air. A blower running over a wet coil with no cooling happening evaporates that moisture and blows it straight back into the house. In a dry climate this is harmless. Here it can raise indoor humidity by several points and undo a meaningful share of the system's dehumidification.

Leave it on AUTO. If you want air movement, use a ceiling fan, which costs a fraction as much to run.

3. Turning it off when you leave for the day

Sensible advice in a dry climate. Here, a house left unconditioned in August absorbs heat into the structure and takes on moisture through every path available, and when you get home the system has to remove both. The recovery run is long, the house feels clammy for hours, and the saving is smaller than the discomfort suggests.

Set it back a few degrees rather than off. Somewhere around 78 to 80 °F while you are out keeps humidity under control and still cuts run time. The same logic applies to an empty house over the season, where switching the system off entirely is how mould problems begin.

4. Closing vents in rooms nobody uses

The intuition is that closing a vent stops paying to cool that room. What actually happens is that the blower keeps moving the same volume of air against a smaller opening, static pressure rises, airflow across the coil drops, and the coil runs colder than designed. Push it far enough and it freezes.

Duct systems are designed as a balanced whole. Closing more than one or two registers unbalances them, and in a house with leaky attic ductwork the increased pressure pushes more air out through the leaks rather than into the remaining rooms.

5. Judging comfort by temperature alone

A house at 78 °F and 48 percent relative humidity feels comfortable. The same house at 74 °F and 65 percent feels unpleasant and costs more to run. Moisture is what makes a room feel heavy, what makes the floor tacky, and what grows on the bathroom ceiling.

A cheap hygrometer settles more arguments about the air conditioning than anything else you can buy. Aim for 45 to 55 percent indoors. If temperature is holding but humidity sits above 60, the system is cooling without dehydrating properly, which usually means it is oversized, short cycling, or moving too much air across the coil.

6. Expecting a filter to last three months

Manufacturers' intervals assume a system running a fraction of the hours yours does. A one-inch filter in a Florida house through the summer is often loaded in a month, and a loaded filter starves the coil of airflow with the same consequences as closed vents.

Check monthly. Replace when it looks grey and packed, not when the calendar says so. Thicker media filters last longer, but only fit where the equipment was built for them, and forcing a high-restriction filter into a system designed for a cheap one trades dust for airflow.

7. Landscaping the outdoor unit into a corner

The condenser rejects the heat from your house into the air around it. Hedges planted tight to the cabinet, a fence built for looks, or a lattice screen recirculate that hot air back through the coil, and the system works against its own exhaust.

Give it a couple of feet of clearance on all sides and nothing overhanging within about five feet above. Keep grass clippings out of the coil; a mower throwing cuttings at the fins packs them in a way that is genuinely hard to reverse.

8. Ignoring the drain until it ignores you

The system produces gallons of condensate a day in summer and it all leaves through one small line. That line stays damp year round, which is ideal for the biological growth that eventually blocks it. A blocked line means a full pan, and a full pan means either a float switch shutting the system down or water on the ceiling.

Pour a cup of distilled vinegar into the drain access every month or two during cooling season. It is the cheapest preventive act available in the whole system.

9. Assuming a technician will be free in July

Service capacity in Southwest Florida is seasonal in a way newcomers underestimate. Book maintenance in March and October, when there is time to do it properly, and know who you would call before you need them. Local companies publish what they actually cover, and a service list such as https://acromanservice.com/ is a reasonable map of the work that gets called out here, from diagnostics through to ductless installations.

Storm season adds its own arithmetic. After a named storm the queue runs days deep, so an outdoor unit that was submerged, or a system that has been running on a generator not sized for its starting current, joins a long line at the worst moment.

Two beliefs that are half right

"A bigger unit will cool the house better." It will cool it faster and dehumidify it worse, and in this climate the second half dominates. Removing moisture happens gradually over a long run, so a system with too much capacity satisfies the thermostat in a short burst and shuts off before the coil has done much drying. The result is the cold, clammy house people describe as feeling like a basement. Oversizing also multiplies start cycles, and compressors wear through starts more than through hours. Capacity should come from a room-by-room load calculation, not from the assumption that more is safer.

"Closing the blinds is a gimmick." It is not. Solar gain through glass is one of the largest components of the cooling load in a Florida house, particularly on west-facing windows in the late afternoon, when the outdoor temperature is near its peak and the sun is low enough to shine straight in. Closing blinds on the sun side before the heat arrives, rather than after the room is already warm, measurably reduces run time. Exterior shading works better still, because it stops the energy before it passes through the glass, which is the logic behind the deep overhangs on older Florida houses.

Frequently asked questions

Do ceiling fans lower the room temperature?

No. They move air across skin, which speeds evaporation and makes a person feel cooler. In an empty room a ceiling fan adds a small amount of heat and no benefit, so turn them off when you leave.

Is a smart thermostat worth it here?

The scheduling matters less than in a climate with big daily swings, but the remote alerts are genuinely useful, particularly for a house that sits empty part of the year. Being told the indoor temperature is climbing while you are away is worth more than the algorithm.

Should I run a dehumidifier?

A correctly sized, well-maintained air conditioner should hold 45 to 55 percent on its own. Persistent high humidity is a symptom worth diagnosing rather than masking, though a whole-house dehumidifier is a legitimate solution in some houses once the equipment has been checked.

How low can I set the thermostat safely?

Below roughly 70 °F many residential systems begin to run the coil cold enough to ice, particularly at night when the load drops. If you want a colder house than the equipment will deliver without freezing, that is a sizing and airflow conversation, not a thermostat one.

Current as of September 2026.