Answer:
  Koei-reisetsu, Inc. kindly answered the above question.
 
  First, Freon tends to leak from tiny gaps in the cooling system which includes the compressor, condenser, evaporator, and so on. The gaps are caused when metals in the cooling system become rusted or corroded or when they often vibrate, expand or shrink. In fact, most metal tubes that are used for cooling systems are made of copper, which can be weakened by some chemicals such as salt.
 
  At present, according to the 2002 by-law, Freon has to be eliminated from all discarded refrigerators, home, and automobile air conditioners when they are disposed. However, in the past, some refrigerators or air conditioners were disposed without eliminating Freon, leading to air pollution.
 
  In addition, manufacturers are no longer permitted to produce new CFC due to its destructive nature against the ozone layer. HCFC is less destructive towards the ozone layer and is now used instead of CFC. However, it seems likely that most manufacturers will switch to HFC from HCFC in the near future. 
 
*Abbreviation
CFC: Chloro Fluoro Carbon
HCFC : Hydro Chloro Fluoro Carbon
HFC : Hydro Fluoro Carbon
 
 
Acknowledgement
Koei-reisetsu, Inc.
They deal with refrigerating systems. There are detailed explanations about the contents of their work on their website.
 
 

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