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You don't need to understand any specific technical details. Just the general physics principles that are involved (i.e. why/how is the heat transferred out of the fridge).
Context: I had a discussion where the topic of refrigerators came up, and I considered it to be a widely known principle. But so far, the vast majority of people I asked never learned or questioned how do fridges actually work (however, most people do seem to know there is some sort of motor and some coolant inside). I think HN is definitely a biased source of data, but still I think it would be interesting to see how common this knowledge really is.
Finally: there's no shame in not knowing/caring how refrigeration works. Please don't turn this into "I know this one random fact hence I'm more knowledgeable". Save that for a whiteboard interview :)