Auto mode lets the AC decide how to run. On mini splits and heat pump room units, it picks cooling, heating or fan only to hold your set temperature and controls the fan speed itself. On a central thermostat, Auto is usually the fan setting: the blower runs only while the system heats or cools.
Auto mode on an AC lets the unit decide how to run. On mini splits and heat pump room units, Auto picks cooling, heating or fan only to hold the temperature you set, and it controls the fan speed for you. On a central system thermostat, "Auto" usually means the fan setting: the blower runs only while the system is heating or cooling.
Two different settings called Auto
Most of the confusion comes from makers using one word for two features. Your remote or thermostat may have either one, or both. Our guide to every AC mode covers the rest of the buttons.
- Auto as an operating mode sits on the Mode button next to Cool, Dry, Heat and Fan. The unit chooses which of those to run.
- Auto as a fan speed sits on the Fan button next to Low, Med and High. You still pick Cool or Heat, and the unit only changes how fast the fan blows.
A central system adds a third use. The fan switch on the thermostat has Auto and On. Carrier's guide to AC thermostats says that in Auto the fan only runs when the compressor is actively cooling the air, while On runs the fan continuously.
| Brand | What "Auto" means | Where it is documented |
|---|---|---|
| Daikin (FTX30NVJU, FTX36NVJU) | A mode that selects Cool or Heat, plus an Auto airflow rate | Operation manual, pages 11 and 13 |
| Midea (MAW08V1WBK window inverter) | A mode that selects cooling, heating or fan only, plus an Auto fan speed | User manual, pages 22 and 23 |
| MrCool (DIY and Olympus remotes) | A mode that selects Cool, Fan or Heat | Remote control user manual, page 6 |
| Senville (RG66B6 remote) | A mode that selects Cool, Fan, Heat or Dry | Remote controller manual |
| Frigidaire room air conditioners | A fan speed on the Fan speed button | Frigidaire features and settings page |
| Central thermostats (Carrier) | The fan runs only while the system heats or cools | Carrier AC thermostat guide |
How Auto mode works
Every manual we opened describes the same basic idea: you set one temperature, and the unit compares it with the room and picks a mode. The makers differ on which modes Auto can choose.
Daikin's operation manual for its FTX30NVJU and FTX36NVJU says that in Auto the system selects Cool or Heat based on the indoor temperature, then reselects at a regular interval to bring the room to your setting. You can set Auto between 64 and 86°F. If you start a Daikin heat pump with the button on the indoor unit instead of the remote, it starts in Auto at 77°F with the fan on Auto.
Midea's user manual for its window inverter units says Auto selects cooling, heating or fan only, depending on the temperature you set and the room temperature. On cooling-only models, heating drops out of that list. MrCool's remote control user manual lists Cool, Fan or Heat. Senville's remote controller manual goes further and lists Cool, Fan, Heat or Dry.
Midea, MrCool and Senville all make the same point: you cannot set the fan speed in Auto mode. Midea says the fan starts at a speed chosen according to the room temperature. MrCool says fan speed cannot be set or adjusted by the user.
Not every unit has an Auto mode. Daikin's cooling-only models list only Dry, Cool and Fan on the Mode button, because there is no heat to switch to.
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Auto fan speed
Auto fan speed is a smaller change. You keep the mode you chose, and the unit adjusts the fan. Daikin lists Auto, indoor unit quiet and airflow rates 1 to 5 on its Fan button. Midea's window units offer Auto, Low, Med and High.
Frigidaire's room air conditioner features page says its Fan speed button cycles through Auto, HI, MED and LO, and that some cycles change the fan speed based on the unit's programming. So if your fan seems to speed up and slow down by itself, Auto fan is the likely reason.
ENERGY STAR's ductless heating and cooling page recommends the "auto fan" setting, or the lowest fan speed that still spreads the air far enough for your needs.
When to use Auto mode and when not to
Auto mode is a convenience feature. It suits a room where you want one temperature held and do not want to switch between Cool and Heat yourself.
On heat pumps, ENERGY STAR advises the opposite for everyday use. Its ductless page says to avoid Auto mode and set the heat pump to "heat" or "cool", so the system does not switch modes during unseasonably warm or cold days. If you see your mini split heating on a spring afternoon when you expected cooling, that is the switching ENERGY STAR is describing.
Auto is also not the setting for a sticky room. If the problem is humidity rather than heat, Dry mode is built for it; see our guide to dry mode on an AC. If you only want air moving without cooling, use fan mode instead.
If the room never gets comfortable in any mode, check the filter first. Daikin's manual says clogged filters cause inefficient operation and waste energy, and suggests cleaning them about every 2 weeks. After that, try our steps to reset your air conditioner.
How to turn on Auto mode
The steps are close to identical across brands that use a handheld remote:
- Press the Mode button until Auto shows on the remote screen.
- Set the temperature you want with the up and down buttons.
- Press On/Off to start the unit.
Those are MrCool's steps, and Senville's remote manual gives the same three. On a Daikin ARC466A37 remote, the Mode button steps through Auto, Dry, Cool, Heat and Fan. On a Midea window unit, the order is Auto, Cool, Dry, Heat and Fan. For Auto fan speed, press the Fan button instead until Auto shows.
On a central thermostat, the fan setting is usually a separate switch or menu marked Fan, with Auto and On. The DOE's Energy Saver guide says to set it to Auto unless an indoor air quality professional has set up your system to run continuously for health reasons.
Does Auto mode save energy?
None of the manuals we opened claims a saving for Auto mode itself, and we found no DOE or ENERGY STAR figure for it. What the government sources do say points in two directions:
- ENERGY STAR recommends the auto fan setting on ductless systems.
- ENERGY STAR recommends avoiding Auto mode on heat pumps.
- Carrier says a central fan left on On consumes extra electricity compared with Auto.
The setting that changes your bill most is the temperature, not the mode. Daikin recommends 78 to 82°F for cooling. Our guide to saving money on air conditioning covers the other habits that help.
Frequently asked questions
Is it better to leave my AC on Auto or Cool?
For a heat pump or mini split, ENERGY STAR recommends setting it to Heat or Cool rather than Auto, so it does not switch modes on unseasonably warm or cold days. Auto suits a room where you want one temperature held year round and accept the unit switching for you. On a cooling-only unit there may be no Auto mode at all.
Why can't I change the fan speed in Auto mode?
Because the unit controls it. Midea's window inverter manual says the fan starts at a speed set according to the room temperature, and MrCool's and Senville's remote manuals say fan speed cannot be set in Auto mode. If you want a fixed fan speed, choose Cool or Heat and set the fan yourself.
Should my thermostat fan be on Auto or On?
Auto, for most homes. The DOE's Energy Saver guide says to set the thermostat fan switch to Auto unless an indoor air quality professional has set up your system to run continuously for health reasons. Carrier notes that On runs the fan continuously and uses extra electricity.
Why did my AC start heating in Auto mode?
In Auto, the unit compares the room temperature with your setting and picks a mode. Daikin says its units reselect the mode at regular intervals, so a cool room below your set point can trigger heating on a heat pump. ENERGY STAR describes exactly this switching as the reason to avoid Auto on heat pumps.
Founder of Home Caprice. Ben started the site to simplify HVAC after dealing with the heating and cooling in his first apartment.