Compressor scrap is any unserviceable air conditioning or refrigeration compressor collected for the purpose of sale as scrap metal. The compressors are typically stored separately from other scrap metal for a number of reasons. The first is the potential presence of contaminants such as oil and residual refrigerant gas in the compressor housings. The second is the fact that the compressors are sealed units containing several types of metals requiring a separate billing system to that applied to single metal scrap material. These metals typically include aluminum, steel, cast iron, and copper.