The metal skin around the door openings is cooled by being next to the lower temperatures in the refrigerator and freezer, so in warm or humid environments condensation can form there. To compensate, there's a low current heating element running around the door openings to warm the metal enough to prevent the condensation.
The climate control switch turns the heater on or off. If you notice condensation, turn it on. You'll use more 12 volt power, but the added draw is only significant when you're boondocking.