Should I have the fan switch turned to "ON" or "AUTO"?

"On" is going to keep your blower running constantly, regardless of heat or A/C running. Auto will only turn on your blower when either of those are called for. If you have a built in humidifier or a high end air cleaner you could chose to run your blower all the time. The typical setting however is to put it on "Auto"

Good Luck,
Morrowrj

Typical setting would be auto, however in some larger houses some prefer leaving the fan set to "on" continuous, some say it gives you a more even temp. throughout the home, and studies have been done , it actually saves the life of your indoor blower motor to run it continuous, it may cost you a few extra bucks a month (depending on the size) but it saves the life of the start windings on your motor. Hope this helps

Auto gives you better control of the temperature. If you want air circulation you can choose on however often it just distributes the cold/hot are already in the room while not providing a steady temperature.

Auto gives you better control of the temperature. If you want air circulation you can choose on however often it just distributes the cold/hot are already in the room while not providing a steady temperature.

I disagree, in all the years that I have done this every customer that runs there system on continuous would not have it any other way... That is a matter of opinion

I will defer to hvacservicetech_07 on this as he obviously has more experience than I.

Unless you have a need to run it all the time, such as special air filtration or humidifiers, its your own choice. There's advantages and disadvantages either way. I personally believe it's a waste of money to run my own continuously.