SHOULD I SET MY AC FAN TO ON OR AUTO?
March 26th, 2023
On your HVAC system’s thermostat, you will see a fan setting, which can be set to ON or AUTO.
The fan is the blower, which circulates cold (or hot) air throughout your home until the temperature on the thermostat is reached.
Central air conditioning works in cooling “cycles”. With an ON setting, the fan stays on all the time that the HVAC system is running. The AUTO setting automatically cuts out the fan when the desired temperature is reached—until the next cooling cycle kicks in.
Which is the correct setting? Should you set your AC fan to ON or AUTO for the most comfortable and efficient cooling performance?
Let’s find out…
Table of Contents
SET AC FAN TO ON OR AUTO?
There’s no “right” or “wrong” setting for your AC fan and your choice may come down to personal preference. However, an AUTO setting is more suitable for most homes as it balances efficient cooling and comfort with the protection of the essential blower motor parts, preventing them from overworking and requiring AC repairs or replacement parts.
There are some instances when an ON setting may be beneficial, however.
Let’s look at the main differences between the settings and the pros and cons of switching the thermostat’s fan setting to AUTO or ON so that you can see why AUTO is generally the favored option…
STAY COOL ALL YEAR ROUND WITH ONE WAY AIR…
The team at One Way Air installs, services, and repairs all types of air conditioning systems in Southwest Florida. Get in touch with us here for a quote or call 239-233-4356 in emergencies.
ON and AUTO AC fan settings: What’s the difference?
When you turn your air conditioning on, it runs constantly—but the active cooling cycles are intermittent.
The first cycle begins when the unit is turned on until the desired temperature specified on the thermostat is reached. The unit then “rests” until the temperature rises again and the next cooling cycle begins.
If your fan setting on the thermostat is ON, the blower motor runs all the time, even when the cooling cycle has ended and regardless of the inside temperature—until it is switched to AUTO or the AC unit is turned off.
When the setting is AUTO, the blower motor stops running when the cooling cycle stops.
The main differences between the ON and AUTO fan settings are the effects on comfort levels, electricity usage, air purity, and wear and tear on parts.
As mentioned, although the AUTO setting is generally preferable, there can be some benefits of leaving the fan on. But before we consider all the pros and cons of each setting, let’s look at the three main considerations before deciding…
MAIN CONSIDERATIONS WITH ON AND AUTO MODE
The three main factors involved in deciding whether to switch the AC fan to ON or AUTO are:
1. Comfort
What feels comfortable for one person may not be the same for the next. Comfort is personal and there are no hard and fast rules.
Keeping the AC in ON mode in summer means that cool air can circulate throughout your home all the time that the AC is operational, with less likelihood of hot spots forming and a more even “cooling effect”.
Keeping the AC fan in AUTO mode may help to dehumidify the home as the moisture can collect inside the air conditioner and drain away from the home. However, the lack of moving air when the fan is off may decrease comfort levels if there are many occupants inside the home.
2. Energy efficiency
The AUTO setting wins hands down when it comes to energy efficiency and minimizing electricity bills. With AUTO, the fan only powers up when the cooling cycle is happening.
Leaving the AC fan in ON mode uses electricity as long as the air conditioning is on. Some estimates suggest you will save $215-$300 per year by running the AC fan in AUTO over ON—maybe more in Florida where AC is so heavily used.
3. Air purity
Setting the AC fan to ON means that the air is constantly being sent through the HVAC filter, which removes dust and other unwanted particles. This may be beneficial if you have allergy sufferers in the home—though it may also increase humidity, which can be harmful for allergy sufferers.
When the fan is in AUTO mode, the air is purified only when the cooling cycle is in effect. The upside of this is that the air filters need to be changed or cleaned less frequently than when the AC fan is set to ON.
When can the ON setting be beneficial for the AC fan?
One way to approach this is to leave the fan in AUTO unless you’re doing a deep clean. When cleaning, switch the fan to ON to remove dust, dander, and other stirred-up particles. Just remember to switch the fan setting back to AUTO afterward.
You might also turn the fan to ON if you have many guests over for an indoor gathering as this can prevent the air from feeling too stuffy.
Another time to use the ON setting is if your indoor AC unit is frozen and you need to thaw it out (more about this below).
AC FAN ON & AUTO: PROS AND CONS
AC fan AUTO: Pros
- More energy-efficient as less electricity is used to power the blower motor (lower electricity bills).
- The AUTO setting helps to dehumidify the home as moisture from the cooling coils can drip and be drained outside.
- May extend the lifespan of your AC unit as it’s not working constantly but enters a type of “rest” mode when the desired temperature is reached.
- Quieter in the home because the fan is not constantly whirring away inside the AC unit.
AC fan AUTO: Cons
- Can increase the wear and tear on the AC fan's motor because it repeatedly turns on and off—though regular AC maintenance will help keep the parts well-lubricated.
- May cause less even distribution of cool air circulating through the home because once the desired air temperature is reached, the fan stops moving the cool air through the ducting.
AC fan ON: Pros
- A more even distribution of cool air circulating through your home, which can help to reduce warm spots.
- Less frequent stops and starts of the blower motor mean less stress on those parts.
- The indoor air quality may be purer if you leave the fan running (fewer dust particles because they get trapped by the air filter all the time the AC is on).
- May be more comfortable if large numbers of people are in your home for a period.
- Can be useful when deep-cleaning the home.
- Can be useful for defrosting an AC unit.
AC fan ON: Cons
- Results in higher electricity bills due to the constant power required to keep the fan running.
- Some systems are not designed for the fan to run constantly and will be overworked.
- You’ll need to clean or replace your AC filter more often as air is constantly being blown through it and cleaned, clogging the filters more quickly.
- May increase humidity in the home as moisture cannot drip away and be expelled outside but blows back into your home when the fan is running constantly.
- AC may have to work harder to remove extra moisture from the air.
- Ducts that run in your attic or close to your outside walls can fill with warm air, blowing hot air into your home and forcing the AC to work harder.
- Maybe too noisy for some people.
WHAT IF MY AC IS FROZEN?
If your indoor AC unit is frozen, the ON mode for the AC fan can be very useful. You can find out what to do in our step-by-step guide to why your AC is frozen and how to fix it.
One of the most important steps is to switch off the AC’s thermostat and turn the fan on. Keep it on for a few hours while the unit fully defrosts. Most times, a few hours is adequate because of the heat in Florida but if you have a large unit and/or it freezes up in the winter, spring or fall, it may take a little longer to thaw.
Once complete, you can turn the thermostat back to a cooling setting and the AC fan back to AUTO.
If the unit is now cooling the home, all is well and good. If warm air is blowing from the AC—or if the unit quickly freezes up again—it’s best to seek professional AC repairs or maintenance. The problem could be anything from a clogged air filter to a faulty condensate pan/drain.
AC IS A MAJOR INVESTMENT—IT PAYS TO LOOK AFTER IT
Like with any other HVAC investment, homeowners should aim to get the most out of their AC, maintain efficiency, and extend its life as much as possible without sacrificing comfort.
The cost of AC in Florida is high—one of the major upfront and ongoing costs for any home—so it will pay to keep it at optimal performance. You do that by understanding more about how the cooling system works and booking regular AC tune-ups—at least once a year before the summer season kicks in.
You can also protect your HVAC setup by promptly troubleshooting your AC unit if you suspect a problem. Call the AC professionals at One Way Air if you are in any doubt.
GET THE MOST OUT OF YOUR AC…
We recommend that you use the AUTO setting for your AC fan most of the time. This should help prolong the life of your unit while maintaining efficiency and comfort.
Our certified professionals can help you optimize your HVAC setup with an annual AC tune-up, regular maintenance, and prompt repairs if necessary.
Keep your family comfortable all year round. Contact One Way Air today.
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Still have questions about your next air conditioner? Let us help you choose an air conditioner you’ll be excited for.
