What Is a Compressor and How Does it Work? An HVACR compressor is a refrigerant gas pump in which the evaporator supplies gaseous refrigerant at a low pressure and increases it to a greater pressure. Upon being compressed, the temperature and pressure of the vapor are increased. The gaseous refrigerant is delivered to the condenser at a pressure at which condensation occurs at an appropriate temperature. A compressor consists of two components: the power source and the compressing mechanism (piston, vane, etc.).