I would not worry about it at temps less than 40. Too little of moisture in air below 40 degrees to add moisture to soybeans in bin. Running the fan in the morning after it has warmed up a couple of degrees will help too if you are still worried about it.

40 degrees 100% humidity 0.00035 lb/cu ft

60 100 0.00083

70 100 0.00116

Running fan at 100% at temps above 60 can cause there to be hard wet soybeans on the floor that will require scraping them off the floor.