Refrigerant BP

[angleslam08]

So I was reading about the carnot cycle and refrigerators in TBR and
it mentioned how you pick the refrigerant (for use in AC/Freezer/Refigerator) based on the Boiling Point and how that since a freezer needs to be a lot colder than other usual appilcances it'd need a Refrigerant with a LOWER BP.... I'm not quite understanding the logic behind that...anyone can explain?

- I figured if it has lower BP then it means it becomes gas easier (higher vapor pressure) and means it'll take less energy to become a gas, so that seems somewhat counterintuitive to me, if it has lower BP, absorbs less energy to vaporize, so it wouldn't make freezer colder? I thought it'd be higher BP would mean colder space in freezer...

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[fizzgig]

you want your refrigerant to boil (which will remove heat from wherever it is boiling) even when it's at a low temperature. if your refrigerant doesn't boil at the cold temp inside your refrigerator, it can't absorb heat from inside the fridge, and so it can't make your fridge any colder. it will make it tougher to compress on the outside of the fridge (to get it to release heat to your kitchen so it's ready for another cycle through the cold space inside the fridge), but that's the price you pay.