A compressor is the heart of a cooling system. It increases the pressure of a gas by reducing its volume.

A compressor is a machine used in cooling systems, among other applications. All compressors work on the same principle, where a compressible media (a gas or air) is added to the compressor at a low pressure. The compressor reduces the size of the media, making the volume less and the pressure higher.
By controlling the pressure of a gas, the temperature at which the gas condenses can be controlled. This is very useful in cooling systems, for example.
There are numerous types of compressors, but all share the same basic function of compressing a gas or air. Some of the most commonly used compressors in cooling systems are reciprocating compressors, screw compressors, scroll compressors, and radial compressors.
The accompanying diagram of a cooling system shows the placement of a compressor.