Sealed system
The closed refrigerant circuit inside a fridge — when it fails, replacement usually beats repair.
The sealed system is the closed loop of [refrigerant](/glossary/refrigerant), [compressor](/glossary/compressor), evaporator, and condenser that does the actual cooling inside a refrigerator or freezer. It's 'sealed' because it's never meant to be opened — a leak or a dead compressor requires an EPA-certified tech to recover refrigerant, braze the line, pull a vacuum, and recharge it, which is why a sealed-system repair often runs $400–1,000+. On a fridge that's already past about 10 years old, that bill frequently exceeds half the cost of a new unit, which is the moment the [50% rule](/guides/appliance-lifespans-and-when-to-replace) says to replace rather than repair. A clicking compressor, a fridge that runs constantly but won't get cold, or frost only on one side are classic sealed-system symptoms.