[8e3k0]

Over a period of 2 1/2 months our fridge has accumulated a lot of frost/ ice on the fins of both the freezer and fridge compartments. The two switches inside the freezer area are for different ambient outside temperatures I assume. The I must be on and the O must be off, is this correct? What actually do these switches do? We do have the manual but it is very vague. If the switches are on will this prevent ice accumulation?
We have a 2009 3400RL with the single door fridge.
Any help or experience would be appreciated. Thanks Ellis