When Running The AC Should The Fan Be On Auto Or On?

Your AC system has a blower that moves warm or cool air around the home. The blower has a small component called a blower fan. The air conditioner fan inside the thermostat determines how your system blows either warm or cool air. You can set the thermostat fan on either auto or on settings. Here is a detailed answer on whether you put the fan on auto or on mode.

What is the Fan Setting on AC?

The fan setting on the AC allows you to choose how the fan will run. There are two options: the on and the auto setting. If you choose the auto setting, the fan will run when the AC starts the cooling cycle. The fan always runs if you choose the on mode, whether the heating or cooling modes.

When Running the Ac Should the Fan Be on Auto or On?

There are pros and cons of setting your AC fan on auto or on mode. It all depends on what you would like to achieve with the settings. If you are keen on using energy, you may choose the auto setting. Your fan will run only when there is a need to do so. This setting will save you energy and give you good indoor air quality.

What is the Auto Mode on AC?

The auto means that the thermostat fan on your AC system begins to run when the system is in a heating or cooling cycle. When the ideal temperature levels are achieved, the fan stops running. The fan begins to run when the next cycle commences.

Leaving your AC Fan on Auto Mode

Leaving your AC fan on auto mode is a personal decision. You may have to consider many factors before you decide to set the blower fan to this setting. Many people like using the auto setting to maintain ideal indoor air quality conditions. For others, using the auto settings helps minimize the amount of energy they use for heating and cooling the air in the home.

Pros of Setting your AC Fan Setting to AUTO

Here are some of the most common pros of setting your AC fan to auto mode.

  • Saving energy. Putting your thermostat fan setting on auto mode helps minimize the amount of energy one consumes. When on the on mode, the fan is always running and uses a lot of energy.
  • Better indoor air quality. If you set your fan on the auto mode, the fan will run only when the system is working. The moisture from the cold cooling coils can then move outside because it will drip. Thus, the air in your home will be in excellent condition because it will not have excess humidity.
  • Longer life for the HVAC system. If your HVAC system is always running, it may get damaged. If the system runs only when there is a need, it may last longer. Also, you may spend less money on repairing and maintaining your HVAC system if it runs on auto mode.

Cons of Setting your Thermostat Fan on Auto Mode

  • Uneven distribution of air in the house. Because the fan does not always run, the cool or warm air may not move around the home.
  • The blower motor fan may get damaged. The blower motor fan consumes a lot of energy when it is starting. If you use the auto setting, the blower fan will start and stop as many times as heating cycles. You may end up wasting a lot of money replacing this component often.

What is the ON Mode on AC?

The on mode on AC means that the fan is blowing the air even when the system is not pushing cool or warm air around the house. The thermostat fan keeps running as long as the AC system is on. This is unlike the auto mode in which the fan runs only when the AC system begins an air conditioning cycle.

Leaving your AC Fan Setting on ON Mode

Leaving your air conditioning fan on is a personal decision. There are various pros and cons of always leaving your air conditioning fan. Consider all the factors before deciding which mode to leave your thermostat fan.

Pros of Setting your AC Fan Setting to ON

Here are some of the most important pros of putting your thermostat fan setting on mode.

  • Even distribution of warm and cool air. When the thermostat fan is always running, it distributes air evenly around the home. The conditioned air flows even if the cooling coils are not actively running. If the fan runs only during cooling cycles, you may end up with cold spots in your home. Thus, whereas auto means that the fan is not always on, it may build up hot and cold spots. If you change the fan settings to always-on mode, the conditioned air uniformly moves around the entire room.
  • Cleaner air. You will have cleaner air because the air will constantly be passing through the filters. The air passing through the filters constantly through the air filters keeps the indoor environment clean. However, you may end up spending more money frequently replacing the air filters.
  • Adjusting the fan setting controls to the mode will help reduce the stress on frequent starts. In addition, you are unlikely to place a service call to repair damaged components if your fan is constantly running.

Cons of Setting your AC Fan to ON

  • If you maintain your thermostat setting at the on mode, you may end up spending more money on higher energy bills. The blower fan and other components end up consuming a lot of power. Thus, you will likely experience a high electric bill if you keep your fan on the on mode.
  • The house may feel much cooler. It may not be easy to maintain the desired temperature in your house if the fan tuns constantly. Cool air may come from the vents in your house during the winter or any other particularly cold day.

Does the Outside AC Fan always Run?

If the setting of the outside fan is set on the on mode, it will always run. However, if you set it on the auto mode, it will run only when the HVAC system runs. This means that the fan turns will not be continuous.

Why does the Fan Keep Running on my Air Conditioner?

If the air conditioner fan keeps on running, it means that there is a problem with your system. The fan is not supposed to be blowing air always. Ideally, the fan should switch on and off as the HVAC system delivers cool and warm air.

The Fan Setting is ON on the Mode

You should always use the auto setting on your system. This prevents the fan and the HVAC’s system blower from running endlessly. If you leave the fan setting on the on mode, it will keep running, much to your chagrin. Therefore, always check that you are using the auto setting on your system.

The AC System is not Working Properly

Sometimes, your AC system may fail to work properly because it cannot handle the prevailing air conditions. If the temperatures are too high, your AC system may fail to blow sufficient cooling air to maintain the indoor air quality. Similarly, if the temperatures outside are too low, the air conditioner may fail to blow enough amounts of warm air to keep you comfortable.

A Short Circuit

A short circuit may occur anywhere in your HVAC system. The air conditioner fan will not receive communications from the settings if this happens. Thus, even if you set your fan on the auto mode, it will continue running because of the short circuit.

A Damaged Thermostat

The thermostat senses the changes in the temperature in your home. If this small component fails to do this because of damage, your fan may end up running without stopping. The thermostat must be in excellent condition to sense what is happening and send the right signal to other components of the ac system.

AC Fan ON or Auto FAQs

Is It Ok to Run Ac Fan All the Time?

It is not necessary to run an AC fan all the time. You will end up spending a lot of money using more energy. Besides, if the fan is always running, the entire air conditioning process may not occur properly. Your house may be unnecessarily cooler during the cold days.

Should Fan Be on Auto or on for Heat

You can keep your fan either on auto or on settings for the heat. When the fan is on auto settings, it will automatically switch on and off according to the changes in your home’s temperature. If you put it on the on mode, it will remain running whether the temperature falls.

Thermostat Auto vs ON

When you set your thermostat on auto mode, it works according to the temperature in the surroundings. When the temperature falls to a certain level, the thermostat sets off the entire system. When the temperature rises to a particular level, the thermostat stops heating.

What does Auto Mean on Thermostat?

The auto setting in a thermostat enables the thermostat to control the air conditioning process according to the prevailing weather conditions. The auto setting is good because it ensures that the system works when it needs to. Thus, the heating and cooling take place according to the ambient temperature in your home.

What does the Fan on the Thermostat Do?

When the fan on a thermometer is on, it means that the fan is constantly blowing air. This may lead to higher energy costs because the fan consumes energy as it runs. The fan does not go off if you set it on the on mode.

Should an AC Fan be on Auto or Circulate?

The AC fan should be in auto mode. This will maximize its air conditioning performance without creating excess energy bills. Also, when the AC fan is on auto mode, it will not unnecessarily create cold drafts inside the home during wintry days.

Should the Outside Fan Run when AC is ON?

The outside fan should run only when the system is on. However, the outside fan should always be running. If the outside fan is always running, there must be a problem with the entire HVAC system.

When to Use Fan Mode in AC?

You should use the fan mode in your AC when the humidity and temperature are within acceptable levels. While using the fan mode, all that the system does is circulate air around the house. Thus, use the fan mode when the temperature and humidity levels are too low or too high.


You can put the fan settings of your AC either on the on or auto mode. The choice depends on several factors. However, it is always a good idea to keep the settings on the auto mode.

This is because when you put the settings on the auto mode, the fan will automatically adjust its performance according to the changes in the weather.

In addition, this will save you money that you would otherwise use if you let the fan always run on the on mode.