Riddle: an open freezer in a sealed room

An empty room is perfectly insulated from the outside world. Inside it, a freezer is plugged in and running, with its door wide open. What happens to the temperature of the room?

Answer

The room gets warmer.

A freezer does not make cold. It is a heat pump: it moves heat from its inside to the coils at the back. With the door open, the inside and the coils are in the same room, so the heat it moves just goes around in a loop.

What is left is the electricity the compressor draws. In a closed room, all of that energy ends up as heat. You would feel cold air near the open door at first, and the freezer would run nonstop, but the average temperature of the room keeps rising for as long as it runs.

Same reason an open fridge will never cool a kitchen.