Today’s discussion: Refrigerant piping.
The indoor coil and outdoor unit are both connected via the refrigerant tubing line set. Routinely, line sets require they be cut to fit, which means care must be taken during the cutting process to prevent copper shavings from being introduced during the deburring process (i.e., removing the ridges inside the tubing created by the pressure of the tubing cutter.) Caution also needs to be used while the refrigerant lines are open and exposed to the job site surroundings to ensure that foreign material is not introduced into the tubing.
Here’s the bottom line: Anything, (and we do mean ANYTHING,) inside the refrigerant circuit, other than refrigerant and refrigerant oil is a catalyst. Catalysts will cause something bad to happen within the refrigerant system. And the only way to prevent them is to be absolutely certain that the refrigerant line set and the rest of the refrigerant circuit is clean and free of foreign material.
One of the most common catalysts is copper oxide. Copper oxides are the “dark stuff” on the outside of the refrigerant lines that accumulate during the soldering process. Note the picture in this post showing two examples of a brazed copper connection, one with and one without dry nitrogen during the soldering process. As you can see, copper oxides accumulate on the inside of the piping too if dry nitrogen is not used during the brazing process.
Copper oxides cannot form unless there is oxygen and high temperature present. Obviously, there isn’t much we can do about the high temperatures during brazing, but we can eliminate the oxygen.
Purging the refrigerant circuit with low pressure dry nitrogen displaces (removes) the air (oxygen) inside the refrigerant circuit while the brazing process is underway. And it’s a good idea to allow the nitrogen to continue to flow for a couple minutes after the brazing is completed to allow the refrigerant lines to cool down so that residual heat in the tubing does not allow the formation of oxides.
Many technicians don’t believe that using dry nitrogen during the brazing process is a critical detail of quality installation, so they ignore it. The reality is that copper oxides are responsible for a significant number of refrigerant circuit restrictions and system failures. Doing whatever we can to prevent copper oxide formation within the refrigerant circuit will help prevent future problems associated with chemical reactions within the refrigerant circuit.
More on additional catalysts in the next post.