Should you shut the AC off for the summer? No. Here's exactly what to set instead.

The answer, then the reasons

Leave it on. Set the cooling to roughly 78 to 82 depending on how long you’ll be gone and whether the house has humidity control, leave the fan on auto, and make sure someone or something can tell you if it stops. The system in an empty Gainesville house is not there to keep anyone comfortable. It’s there to pull water out of the air, and from May through September the air carries a lot of it.

What happens to a house with the system off

Gainesville’s summer dew point sits in the low to mid seventies for weeks. A closed house with no air movement and no dehumidification climbs to match it within a day or two, and once the indoor humidity is above about sixty-five percent for a sustained period, mold has what it needs. Closets go first, because they’re the stillest air in the house; leather, books and wooden furniture follow. Drywall behind furniture and the back of a closet against an exterior wall go next. By the time a student returns in August or a faculty family returns from a summer abroad, the house smells, the clothes are spotted, and the fix is remediation, not cleaning.

The air conditioner at 80 prevents all of this, because the problem was never temperature. It was moisture, and the only piece of equipment in the house that removes it is the coil.

Settings for different absences

Who’s leaving	How long	Cooling setpoint	Fan	Humidity target
Student, apartment, standard system	Summer term, roughly three months	About 80	Auto	Whatever the system holds at 80; check the lease
Faculty or family, single-family house	Three to ten weeks	78 to 80	Auto	Below 60 percent if a thermostat reports it
Lake house or weekend place near Waldo or Earleton	Months at a stretch	80 to 82 with a whole-house dehumidifier	Auto	55 to 60 percent via the dehumidifier
Landlord-owned unit between tenants	Two to twelve weeks	About 80	Auto	Same as above; add a drain float switch if there isn’t one

Two settings to avoid. “Off” for the reasons above. And “fan on” rather than auto: a fan running between cooling cycles blows the water off the wet coil back into the house and raises humidity, which is the opposite of the goal.

Call 866-266-5709

Before you lock the door

1. Change the filter. A filter loaded with the spring pollen season restricts airflow for three months with no one to notice the frozen coil.
2. Clear the condensate drain or have it cleared, and confirm the float switch works. A clogged drain in an empty house shuts the system off, and then the house is at the mercy of the humidity for however long nobody checks.
3. Set the thermostat per the table, and if it’s a smart model, confirm the app shows the house and sends alerts for temperature and humidity.
4. Close the blinds on the west and south windows to cut the load.
5. Leave interior doors and closet doors open so the air circulates through the stillest spaces.
6. Turn off the water heater or set it to vacation, and if you turn off the water supply, know that a condensate drain that relies on a trap primer may dry out.
7. Arrange a check. A neighbor who walks through every two weeks, a property manager, or a technician on a schedule. The failure that ruins a house is the one that goes unnoticed for a month.
8. Unplug what you can and consider a surge protector at the panel; summer lightning doesn’t take the summer off.

What a landlord or manager should do differently

A unit between tenants is the highest-risk case because no one lives there and no one is paying the electric bill with interest. Set it at about 80, confirm the drain and float switch, and put the unit on the turnover sweep list. A unit that sits in July with the system off is a unit that gets painted twice.

Storm season while you’re away

Gainesville is inland, but Helene in September 2024 left tens of thousands in the county without power, and the restart surge when power returns is hard on boards and thermostats. If you’re away during a named storm, a smart thermostat tells you whether the system came back. If it didn’t, a one-visit restart or a board replacement in the first week is a small job; the same failure discovered a month later is a remediation job. We can be the number a neighbor or manager calls.

When you get back

If the house smells musty despite the system running, the coil and drain pan probably grew what the humidity fed them. A coil cleaning and a drain treatment put it right, and a UV lamp at the coil is a reasonable addition for a house that’s empty every summer. If the house smells musty because the system wasn’t running, call 866-266-5709 and we’ll find out why, from the Palm Coast headquarters at 37 Fairmont Ln, about two hours out, at any hour and at the same price as any other day.