I've had a 15 cu ft chest freezer converted into a keggerator for 3 years now. Since day one it's been set at 36, with the cooling turning on at 40. Just recently, I've noticed the keg diagonally opposite the temp probe has been freezing, first a dunkelweizen, then my soda water. The probe hasnt moved in 3 years, the temp settings haven't changed, but that corner does seem to be icing up preferentially. Any thoughts?