Should AC Fan Be On Auto Or On? A Simple Guide For You

Liz Yang

If you have a central air conditioning system at home, the thermostat will usually have an “auto” and “on” symbol for controlling the AC fan.

So, what is the difference between “Auto” and “On”? What are the pros and cons of these two settings?

These are questions that many of my friends have posed to me. So I’ve decided to share what I know about this topic with you in this post. Don’t be alarmed! After reading this article, you should be able to determine which setting is best for you.

What does the “Auto” setting mean?

The air handler contains an AC blower fan that is in charge of directing conditioned air into the room. This fan’s operation is controlled by the “Auto” and “ON” settings.

When the AC blower fan is set to “auto,” it will turn on when cooling or heating is required and then turn off when the cooling or heating cycle is complete.

It’s worth noting that some split or window air conditioners include an “auto mode,” which is an AC mode that can automatically heat or cool the room. As a result, it is entirely different from what we are discussing in this post.

Pros of using an Auto setting 

In fact, many HVAC experts recommend that we leave the AC fan setting on “Auto.” You’ll see why they say that after reading the benefits listed below.

Save energy

It will save a lot of electricity because the fan will stop working when the air conditioner is turned off. The AC fan, as you are aware, consumes a few hundred watts per hour. It will save you more money in the long run if it can take a break from time to time.

Less tear and wear

Again, because the fan is not required to run continuously, it will experience less wear and tear. You can anticipate the blower fan lasting longer.

Better dehumidifying effect

When the air conditioner is turned on, it dehumidifies the air by converting the water vapor into the collected water. The water will drain via the drain tube.

When the compressor is turned off, a portion of the water continues to drain, while the remainder remains on the evaporator coil and in the drain pan.

If you are sensitive to noise, you will appreciate the moment the fan and air conditioner are turned off.

You don’t need to replace the air filter so often

Because the Auto setting allows less air into the air filter, it takes longer for the filter to become clogged. You can reduce the cost of purchasing new filters.

Cons of using an Auto setting 

Uneven temperature distribution in the house

The temperature upstairs is naturally higher than the temperature downstairs. If the fan stops when the air conditioner turns off, the cool air will not be distributed evenly throughout the house, resulting in hot and cold spots.

Lower air quality

The fan can help to improve air circulation in the home. When the AC is turned off, and the Auto mode is activated, the air circulation speed decreases significantly. If the time between cycles is too long, the air can become stale.

What does the “ON” setting mean?

The “ON” setting means that the AC fan will always be on. That is to say, the fan will work continuously regardless of whether the AC is turning on. 

Pros of using an “ON” setting

Balanced air temperature

The hot air or cold air will be evenly distributed all over your house with the help of a fan. You will not feel uncomfortable when you sleep in the room upstairs.             

Improve indoor air quality  

If you have respiratory problems, you will need cleaner air at home. When the air conditioner fan is turned on, it can continue to filter out airborne particles, decreasing the likelihood of allergies.

Cons of using an “ON” setting

More energy consumption 

Because of the continuous operation, energy consumption will rise steadily. Some systems include a multi-speed fan, which can help to alleviate this issue.

The fan motor wears out faster

Since the motor has no time to take a break, the parts inside are easier to break down. 

Higher humidity level 

When the air conditioner is turned off, the fan accelerates the re-evaporation of water left on the coil or in the pan, raising the humidity in the air.

Meanwhile, the continuous operation may cause or worsen duct leakage, allowing more humid air from outside to enter.

Increase the frequency of replacing the filter

The filter needs to deal with more particles lingering in the air, so it requires cleaning or replacement more often. 

Offset the cooling or heating effect 

When the air conditioner is turned off, the duct can fill with more warm or cold air, canceling out the cooling or heating effect of the unit.

When to use the Auto setting?

In most cases, you should leave the ac fan setting on the thermostat at “Auto.” It will help you save money, control indoor humidity, and extend the life of your machine.

When to use the ON setting?

If you are cleaning the house, are prone to allergic reactions, or have a lot of visitors, it is best to change the setting from “AUTO” to “ON.” It will keep the air clean.

AC fan ON or Auto, which one should you choose?

Now that you may already have the answer to this question. 

In general, the air conditioner fan should be set to “AUTO” rather than “ON.” It will save more energy, cause less damage to the fan motor, and aid in humidity control.

However, if the air in the house is contaminated, turning on “ON” is preferable because it will filter out the particles, keeping the house clean and fresh.

Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested a lot of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.