How to Patch an Aluminum Coil w/ AlloySol
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Leaks in aluminum coils are quite common in evaporators and condensers. Although replacement is common in those cases, we can also patch the aluminum coils by soldering them for temporary solutions or even permanent repairs.
You start off by cleaning the aluminum and purging the coil with nitrogen. Even though you may not work at temperatures high enough to promote carbon buildup inside the aluminum coils, it’s still a good idea to flow nitrogen while soldering. Then, you make a hole in the coil (to replicate a rubout). You can pull the fins away from the area gently with a flat-head screwdriver or a small set of pliers.
It is possible to use an oxyacetylene torch with a soft flame for soldering, but it’s probably going to be easier to use a small tip on an air-acetylene torch. (We use a #3 tip.)
AlloySol is a low-temperature rod best used for soldering aluminum instead of brazing. (AlloyBraze also works, but you’ll have the be very careful with it, as it’s meant to be used with higher temperatures.) We use AlloySol by heating up the end of the rod, putting flux on the rod, heating the work area, melting flux onto the work area, and continuing to heat the flux until it goes clear. The flux will cover and then open up the hole; when the hole opens up, it’s time to apply the rod until it’s melted. Some of the fins may melt away during the process; that is normal and will generally be fine for temporary fixes while waiting for a replacement coil.
Patching aluminum can be a permanent solution for leaks on U-bends. For patching U-bends, the soldering procedure is quite similar to the coil soldering procedure. Heat up the rod, dip it in flux, heat the base material, and apply the flux until it melts into the hole and opens it. When you apply the rod, it should go onto the hole like a little blob. Keep applying heat until you have a smooth finish. You can even use a wire brush after the U-bend cools if you want a nice, shiny finish.
Out patches passed the bubble and standing pressure tests.