How to Solder Your Air Conditioner Tube

No. This page is not about how to solder electronic components on a circuit board. Ah. Still remember the good old days when I soldered too much on a circuit board that I have to reheat it, clean it, and make a mess of the whole board. Sob.

That is still soldering, but on a slightly different concept to soldering copper tubes.

Soldering copper tubes are easier, and require an extra step. That step is to apply rosin based flux.

Purpose of this air conditioning maintenance is to join two parts of a metal, especially copper tubes, for air conditioning application.

Soldering is not as strong as welding, but the task can be carried out much quicker, with moderate strength for air conditioning application.

However, the parts that are being soldered have to be overlapping.

How to solder copper tubes. Preparation:

Preparation of soldering material, pipes, and ventilated space is important before we even explore into how to solder copper tubes.

Items that are required include,

  • self igniting flame torch.

    Usually fuelled by propane, and functions as metal heating medium

  • a lead free solder.

    This material will melt upon contact with temperature above 190 oC.

    Consists of tin, silver, and a small percentage of copper

  • a small amount of rosin flux and its brush.

    Comes in small containers. Functions as an etching medium, to remove the oxide layer on copper

  • tube expander,

  • a few emery cloth (also known as sandpaper).

    Used to prepare soldering area on the tube by removing the oxide layer

  • a round wire brush.

    Functions similar to emery cloth, but used to clean internal diameter of the tube

  • a fire blanket.

    Used to prevent nearby material from catching fire from the flame torch

  • a length of copper tubes of required diameter, and the joints

  • a pipe cutter to cut the tubes into required length,

  • a tube bender to bend the tubes to required path,

  • and a few thick cotton rags

Here are the steps on how to solder copper tube:

Preparation list before mosing into how to solder steps


  1. know the route required for the copper tubes,

  2. cut the tubes such that, joint requirement will be minimised,

  3. bend the tubes where possible, but not exceeding the maximum bend radius per tube diameter.

    This data is normally available with the tube manufacturer

  4. expand one end of straight joint tubes, to the outer diameter of the mating tube.

    This is used if you are joining two tubes on a straight joint

    Fabricated joints will have larger diameter than the tubes’ external diameter. Hence, no expansion is required

  5. clean the ends of the joining sections.

    Use sandpaper and round brush for cleaning the mating sections.

    Use sandpaper for cleaning the outside diameter of tube, and round brush for cleaning inside diameter of expanded tubes, or joints.

    Never touch the cleaned parts with your bare hands

  6. apply a small amount of flux to the mating sections,

  7. fit the mating sections as deep as possible,

  8. put fire blanket on the floor, and on adjacent areas to prevent fire,

  9. ignite the torch,

  10. heat the fitted section evenly for about 10 seconds by moving the torch around the tube’s circumference.

    Use the blue flame from the torch as it is the hottest flame region

  11. take a length of lead free solder, and put the tip at the interference of the fitted tubes.

    Give a slight force, so that solder will flow evenly around the circumference

  12. take out the solder piece, and clean excess solder using cotton rag.

    Do these as soon as possible, as cooled solder will stick onto the tube. We’ll have to reheat it to remove it. Not very efficient use of energy.

How to solder step 1: Know the best route for copper tubeHow to solder step 2: Cut and bend the copper tube to be soldered
How to solder step 3: Expand one side of the mating tubes before soldering. Unless if you're using a pre fabricated jointHow to solder step 4: Use emery cloth and wire brush before appying solder
How to solder step 5: Apply flux to the overlapping areasHow to solder step 6: Heat up area to be soldered evenly for 10 seconds
How to solder step 7: Apply solder to the intersection of the overlapping tubesHow to solder step 8: Wipe off excess solder as quickly as possible using emery cloth. How to solder topic is almost completed

Learning how to solder alone is not enough.

Safety is important:

Do not,

  • inhale the smoke from soldering. Solder in a well ventilated space as the fume is toxic,

  • solder near areas with flammable items,

  • touch the heated pipes with your bare hands,

  • solder without wearing leather gloves

And we’re done with how to solder copper tubes.

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