Dairy farmers have been using refrigeration compressors for years to lower the temperature of milk that is harvested to an appropriate storage temperature. The milk must be maintained at that temperature until it is picked up and transported to the dairy. Refrigeration compressors like the Copeland 3D, 4D, and 6D models or Bitzer's 4GE and 6FE models work exceptionally well. Carrier O6E and O6D models are also efficient. All three brands offer reciprocating compressors that cool the milk to the appropriate temperature.