slightly ot: fridge query

I know this is not the ideal place for this but a few weeeks ago i replaced the faulty thermostat in the fridge part of our fridge/freezer. It works fine now but the end of the capillary wire from the stat (which is housed in a plastic cover) is all iced up, this never happened before.
The only difference i can think of is the original one had a plastic tube covering the bare metal wire. Does anyone know if this would make any difference, this is the only part of the capillary wire that is covered. All the rest which loops at the back of the fridge is bare metal wire.
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