Piping, Tubing, Brazing, and Soldering
Materials and joining
Refrigerant lines use ACR copper, which is cleaned and capped; types L and K are used for water and gas piping. Soft soldering with tin-antimony or lead-free solder is for potable water and low-temperature work, never for refrigerant lines. Refrigerant joints are brazed with silver-bearing filler alloys; the higher the silver content, the lower the flow temperature and the better the gap-filling. Flux is used for soldering but must not be introduced inside refrigerant piping, where residue contaminates the system.
The nitrogen purge rule
Whenever refrigerant piping is brazed, flow dry nitrogen through the line. Without it, copper oxide scale forms inside the tube and later plugs screens, TXVs, and filter driers. This is the single most tested brazing concept. Purge with a regulator, not full cylinder pressure, and vent the far end so flow is proven rather than assumed.
Evacuation and charging
After pressure testing with dry nitrogen, evacuate with a vacuum pump and measure at the system with a micron gauge, not at the pump. A standing vacuum test confirms no leaks or moisture; a rise toward atmosphere means a leak, and a slow rise that levels off can indicate moisture. Deep vacuum removes moisture because POE oil and moisture are unforgiving together. Charge by weight where possible, or by subcooling and superheat where a nameplate charge is not practical.
Traps and worked example
Never pressure test with oxygen, and never braze without a fire watch and appropriate shielding. Rule of thumb for a target: evacuate to about 500 microns and hold. If a system holds 500 microns and rises to 1,500 and stays, suspect residual moisture or a small leak; re-purge with nitrogen and repeat before charging.