R744 is just the refrigeration industry's name for CO2. A wide range of substances can be used as refrigerants - basically anything that can be boiled and cond

R744 is just the refrigeration industry's name for CO2. A wide range of substances can be used as refrigerants - basically anything that can be boiled and condensed. This includes the more commonly used ones such as r134a (tetrafluoroethane), r717 (ammonia). Even water can be used as a refrigerant (r718). It's just an industry naming convention for different chemicals.