Tips on Soldering an AC Line Set

Soldering an A/C line set is necessary when you install an A/C unit yourself or your unit breaks. The line set carries the coolant from the condensing unit to the coil located on the top of the furnace. A black rubber insulation wraps the line set. This helps prevent condensation from forming on the line set. Typically, line sets are one-half inch in diameter and require soldering couplings and other fittings in the installation process.


If your line sets break, consider soldering them yourself.

When cutting the line set for your A/C unit, place the tubing cutter onto the copper pipe so the cutting wheel and cooper pipe rest on the line set. Overtightening the tubing cutter will crush the soft copper of the pipe. Turn the tubing cutter one full turn in one direction and another full turn in the opposite direction. Tighten the tubing cutter handle a quarter-turn and repeat the process until your line set is cut. It typically takes two to three times of repeating the process to properly cut through the line set.


Cleaning the line set ends after cutting or before any soldering is essential in performing a proper solder. An emery cloth sandpaper and wire brush are used to clean inside the ends of the line set as well as around the outside of the line set end. Clean the line set until the copper shines. This removes all debris or loose shards of copper from the line set.


Fluxing the end of a line set ensures the solder is properly attached to the line set. Applying flux on the outside and the inside of the copper line and fittings pulls the solder into the cracks of the fittings to maximize the seal of the solder. Fluxing is an essential process of soldering. You may wish to practice fluxing on scrap pieces of copper before you flux the line set to your A/C unit.

Heating Fittings

When heating the copper line set to the A/C unit, do not overheat the copper. Overheating the copper results in an improper soldering connection. Heat the copper only until the flux begins to sizzle. When the flux sizzles, the copper is hot enough to melt the solder. Touch the solder to the copper line set around the entire fitting as the flux pulls the solder into the fitting, ensuring a proper connection.

Heat Shield

Use a piece of galvanized sheet metal in tight areas to act as a heat shield. Place the galvanized sheet metal behind the area being soldered. This prevents your walls from burning or possible fire damage to your home or A/C unit. The sheet metal helps distribute the heat evenly around the fitting as you heat the fitting with your torch.

About the Author

Stephanie Nolan has been a freelance writer since 2005. Her articles appear on various websites, where she specializes in topics about home improvement, parenting and interior design. Nolan holds an Associate of Applied Science degree in business management from the University of Phoenix.