By expansion of a liquid to a gas. You compress a gas to a liquid and feed it through a nozzle to the cooling coil. There the gas rapidly expands and uses energy to do that. The gas can then cool the air in the heat exchanger. It is then recompressed. Just like a fridge. So you have a pump as the main part. Usually the seal on the pump or the control vales fails & gas escapes.
The pump is normally driven off the fan belt.
