Natural refrigerants are among the first refrigerants to beused for mechanical cooling systems. After development of CFC and HCFC refrigerants, use of natural refrigerants reduced. Because of the damage to the ozone layer and the high GWP of CFC and HCFC, refrigerants were phased out. For the same reason, systems which used HCFC refrigerants were replaced with natural refrigerants, mainly hydrocarbons (HC). This procedure is called system conversion and it is increasing throughout the world. Split cooling systems are in use around the world and usually contain the refrigerant R-22. Replaced refrigerants should have similar properties to refrigerants being replaced with minimum modifications of the existing system. The ideal alternative substance for the R-22 is propane (R-290), because it has excellent termophysic properties, is more energy efficient and requires small modifications in the system. The problem with propane and generally with hydrocarbons is that they are highly flammable and explosive. In the implementation of the conversion process,it is very important to follow the safety conditions and standards. When statutory requirements for safety are met, propane is an ideal replacement refrigerant. The first part of this work presents the thermophysical properties of propane compared to R-22. The second part presents which safety conditions and standards should be met. The end contains termodynamic calculations and the comparison between systems with propane and R-22. The drawings at the end show the scheme of the cooling system with propane and R-22, including the necessary structural changes.