Nitrogen purge is the continuous flow of inert nitrogen gas through refrigeration tubing during brazing to prevent oxygen exposure and oxidation that weakens joints and contaminates systems. This critical procedure protects copper surfaces from forming copper oxide scale at high temperatures.
Technical Procedure
Dry nitrogen (dew point -40 degrees Fahrenheit or lower) flows through tubing at 5-10 CFH (cubic feet per hour) during brazing operations. Nitrogen enters through one fitting and exits the other, creating positive pressure that excludes atmospheric oxygen. Flow continues until the joint cools below 300 degrees Fahrenheit. Insufficient flow rates below 3 CFH fail to prevent oxidation; excessive rates above 15 CFH blow filler metal from joints. Regulators and flowmeters ensure consistent delivery throughout the brazing process.
Critical Importance
Unprotected brazing creates copper oxide scale inside tubing, which contaminates refrigerant and damages compressors. Oxidation reduces joint strength by 50-70 percent, leading to leaks within months or years. Nitrogen purge is mandatory per EPA Section 608 certification requirements and HVAC industry standards. Proper purging results in bright, clean joint surfaces and reliable systems lasting 15-20 years without refrigerant loss.