Most air conditioners and refrigerators use the compression cooling circle. The basic thermodynamic principle lies in deflation of gases and liquids: When a gas/liquid deflates it extracts heat from its environment.
Extracting heat means cooling. So when a gas/liquid deflates, it creates a cool environment.The cooling cycle now has to provide a high pressurised gas/liquid which can deflate. The higher the pressure of the gas/liquid, the more cooling will be achieved. So a compressor compresses the gas to a high pressure, it is easier for the compressor to compress a gas in comparison to a liquid, which means less power is needed for the compressor.