Refrigerating machines are considered as dangerous goods for sea transport. Refrigerating machines may either contain non-flammable non-toxic gasses, ammonia solution or flammable, non-toxic, liquefied gas.
There are two entries for refrigerating machines in IMDG Code 35-10
UN 2857, Class 2.2
REFRIGERATING MACHINES containing non-flammable, non-toxic gases or ammonia solution (UN 2672)
&
UN 3358 , Class 2.1
REFRIGERATING MACHINES containing flammable, non-toxic, liquefied gas
There are also exemptions in IMDG Code for Refrigerating machines.
IMDG Code Compliance Centre 