Air conditioner

It doesn't make cold. It carries heat: soaks it up indoors, pumps it outside, dumps it in the hot air.

• Evaporator: refrigerant enters near 5 °C and boils. Boiling soaks up heat from the room air blown across the coil.
• Compressor: squeezes that cool gas until it's hotter than outdoors, often 70–80 °C. Now heat can flow out, even on a hot day.
• Condenser: the outdoor fan blows air across. The hot gas gives up its heat and condenses into a warm liquid.
• Expansion valve: a tiny gap drops the pressure. The warm liquid flashes cold, and the loop starts over.
• The thermostat is just on/off with a 1 °C dead band. Walls leak heat back in, so the A/C kicks on again.