The objective of the use of nitrogen through the brazing process is
internal oxidation of the tube. Oxidation occurs as a function of the presence of oxygen in contact with the wall of the tube when it is heated. The solvent action of the refrigerant removes the buildup of carbon dioxide from the pipe walls and carries this residue with you through the system, which can cause obstructions or damage vital components of the compressor.
With the passage of nitrogen (inert gas) contained in the air pipe is removed, then there will be oxygen when heat is applied and therefore no oxidation will occur. Before starting the brazing, it is recommended to apply nitrogen at one end of the tube and make sure it is coming out in the other.
During brazing, the nitrogen pressure inside the tube must not be high (up to 3 psig), and after completion, it is necessary to maintain nitrogen flow until the wall of the cool tube, and there is the possibility of oxidation (by at least 1 minute).
