The top pipe was brazed with nitrogen, the bottom pipe without nitrogen.
With today’s new more efficient HVAC system designs and related refrigerant changes, about all HVAC installation instructions require flowing nitrogen through the copper tube during brazing. This is an important step in producing a quality HVAC system. Oxygen in the air combines with copper to form on the surface a copper oxide.
At typical brazing temperatures a black oxide forms in the tubing. When the copper tubing cools this oxide flakes off to form a “scale”. While mostly cosmetic on the tube exterior, inside the tube the oxide scale flakes are carried by the refrigerant throughout the system. These flakes are a contaminant that can restrict flow through small orifices such as metering devices or the pilot valve capillary tube in a reversing valve.
The issue of scale is not new. Scale has long been an issue in brazing HVAC tubing. But today it has become very important with the change to the new HFC refrigerants (410a). The new refrigerants have a strong solvent effect and can “scrub” the inside copper tube walls, causing the scale from the tubing walls and any loose scale to circulate.
To prevent this oxidation and make sure your HVAC system lasts as long as possible and delivers its maximum savings, Grimes and Galan takes the extra time and additional small expense to always use nitrogen when called for in system repair and installation. Below are some pictures of David Galan brazing a new install with a nitrogen flow.
(click any image to enlarge)
