Any malfunction of the refrigeration unit associated with a refrigerant leak sooner or later leads the owner to the need to seal the circuit. Soldering tubes is the main method of restoring the tightness of the system, ensuring a reliable connection of metal elements under high pressure. Without a high-quality seam, it is impossible to create a vacuum and fill the refrigerator with freon, so strict technical requirements are imposed on this stage of repair.
The process of joining metals requires not only the presence of special tools, but also a deep understanding of the physics of the solder melting process. Errors at the preparation stage or the heating itself can lead to repeated leakage or, worse, to clogging capillary tube with oxidation products. In this article we will look in detail at how to properly prepare materials, select a burner and make a connection that will last for decades.
Preparation of the workplace and selection of tools
Before starting work, it is necessary to organize a safe space with good ventilation, since the soldering process is accompanied by the release of gas combustion products and flux. The master's main tool is a gas burner, which can operate on a propane-butane mixture or pure propane, depending on the required flame temperature. To work with copper tubes up to 22 mm in diameter, compact torches are often sufficient, but for thicker walls or steel areas it is better to use equipment with oxygen enrichment.
The critical element is eye protection and hands. Bright flames and splashes of hot metal require the use of special glasses with filters and thick gloves made of non-flammable materials. Also, you should always have a fire extinguisher on hand, since work is often carried out in close proximity to the insulating materials of the refrigerator, which are easily flammable.
⚠️ Attention: Never start soldering if there is old freon left in the refrigerator circuit. When heated, it will react with oil and form an aggressive acid that will destroy the compressor from the inside.
A set of tools for high-quality repairs should include not only a fire source, but also devices for processing edges. Pipe cutter provides an even cut without burrs, and Rimmer (expander) allows create the necessary gap for one pipe to fit into another. The lack of these tools often leads to the use of files and sandpaper, which increases the preparation time and reduces the quality of cleaning.
The choice of solder and flux for refrigeration systems
The quality of the connection directly depends on the correct choice of consumables. For copper pipes of refrigerators, hard solders based on silver or phosphorus are most often used. Phosphorus-copper solders (for example, grades BCuP) have the property of self-fluxing when soldering copper with copper, which simplifies the process and reduces the risk of oxidation of the internal walls.
If it is necessary to connect copper with steel (for example, at the outlet of a compressor), the use of simple copper-phosphorus alloys is unacceptable, since they form brittle carbides. In this case, silver solders with a precious metal content from 15% to 40% or specialized alloys for dissimilar metals are used. Such materials provide high ductility of the seam and resistance to vibrations of the working compress.
Fluxes play the role of a reaction catalyst, removing the oxide film from the surface of the metal and improving the fluidity of the melt. However, in refrigeration technology they are subject to special requirements for aggressiveness.
- 🔥 Fluxes must be easily washed off or burn without residue so as not to pollute the system.
- 🧪 Acid fluxes are prohibited, as their vapors can penetrate into the circuit and cause corrosion.
- 💧 Acid-free, borax-based fluxes are the standard for professional repairs.
⚠️ Caution: Excess flux entering the tube can harden and clog the filter drier or capillary. Use a minimum amount of composition.
Technology for connecting copper to steel
One of the most difficult tasks in repair is soldering a copper tube to a steel one, which is often found at the point where the discharge pipe exits the compressor. Steel and copper have different melting points and thermal conductivity, which requires a special approach. The melting point of steel is much higher than that of copper, so it is the steel part that needs to be heated, not the copper. If you heat copper, it will melt before the steel reaches the required temperature for solder to spread.
The process begins with thorough cleaning of surfaces. The steel tube is cleaned to a metallic shine, removing rust and factory coating. The copper tube is also degreased and cleaned. A thin layer of flux is applied to the steel surface, after which heating begins.
It is important to heat the joint evenly, moving the flame around the joint. When the steel is heated to a dark cherry color, a solder rod is brought to the joint. The molten metal should flow into the gap by capillary action, and not just spread on top. After cooling, the seam is wiped with a damp rag to remove flux residues.
Why should you not overheat the joint?
Overheating a steel tube can lead to carbon burning out of the metal, making it brittle. In addition, excessive heating of the copper part can cause it to deform or even burn through the wall if it is thin. The optimal temperature is determined by the color of the heat and the behavior of the solder, which should melt from the heat of the metal, and not from direct contact with the burner flame.
Soldering copper pipes: main stages
Joining copper with copper is a more predictable process, but there are some nuances here too. The main rule is to ensure a tight fit of one pipe into another (into the socket) with a gap of about 0.1-0.2 mm. A gap that is too large will require a lot of solder, which can leak inside, and a gap that is too small will not allow the solder to penetrate deep into the joint.
Heating is carried out in a circle, evenly heating both parts being connected. The burner flame should not be too hard so as not to blow out the molten metal. When the metal reaches operating temperature (about 700-750°C for copper-phosphorus solders), a solder rod is applied to the joint.
The molten solder should itself cover the joint with an even bead. If the solder clumps or rolls off, it means the temperature is insufficient or the surface is not properly cleaned. After forming the seam, it is necessary to allow it to cool naturally, without blowing or pouring water, in order to avoid thermal stress of the metal.
☑️ Quality control of soldering
Table of temperature conditions and materials
To successfully complete the work, the master must be familiar with the properties of various metals and solders. Below are the main parameters that must be taken into account when setting up the torch and selecting consumables.
| Connection material | Solder type | Melting temperature (°C) | Features |
|---|---|---|---|
| Copper - Copper | Copper-phosphorus | 700 - 750 | Self-fluxing, does not require borax |
| Copper - Brass | Silver (15-30%) | 650 - 700 | Required flux, high strength |
| Copper - Steel | Silver (30-45%) | 720 - 780 | Flux is required, heat steel |
| Aluminum | Aluminum alloy | 580 - 620 | Requires special flux and cleaning |
Typical errors and methods for eliminating them
Even experienced craftsmen sometimes make mistakes that can cost the refrigerator its life. One of the most common problems is the formation oxide film inside the pipe due to soldering without nitrogen purging. When copper is heated in the presence of atmospheric oxygen, scale forms on the internal walls, which subsequently comes off and clogs the filter-drier.
Professionals use blowing nitrogen during soldering, creating excess pressure in the circuit, which displaces oxygen. This is difficult to do at home, so it is recommended to minimize heating time and try not to overheat the tubes unnecessarily. Another common mistake is the insufficient depth of insertion of the pipe into the socket, which makes the seam mechanically weak.
Another problem is “cold soldering,” when the solder does not fuse with the base metal, but simply sticks on top. Such a seam looks dull and rough, it is not airtight and collapses at the first vibration. To avoid this, you need to thoroughly clean the surfaces and allow the metal to warm up to the desired temperature before applying solder.
Checking for tightness and finishing work
After all seams have cooled, a visual inspection must be carried out. A high-quality seam has a smooth, shiny surface without visible pores, cracks or sagging. The next step is to pressurize the system with nitrogen or dry air under pressure to check the tightness.
The soldering areas are generously lubricated with a soap solution or a special leak detector. The appearance of bubbles indicates a defect. If the seam does not hold, it must be heated, the old solder removed, cleaned and soldered again. Re-soldering requires special care to avoid burning the metal.
⚠️ Warning: Do not use an open flame to search for freon leaks in a filled system - this may result in an explosion or fire. The test is carried out only with inert gases.
Only after successful pressure testing and evacuation of the system can the work be considered complete. Correctly performed soldering guarantees long and trouble-free operation of the refrigeration unit, maintaining its energy efficiency and cooling performance.
Is it possible to solder refrigerator tubes with ordinary tin solder?
The use of soft tin-lead solders (POS) in refrigeration circuits is highly not recommended. They have a low melting point and insufficient mechanical strength. Under the influence of compressor vibration and temperature changes, such seams quickly crack. Additionally, lead may react with refrigerant and oil. For reliable repairs, use only hard silver or copper-phosphorus solders.
Do you need to change the filter drier after each soldering?
Yes, this is a mandatory rule. The filter drier is designed to remove moisture and acids from the system. With any depressurization of the circuit (and soldering involves cutting the pipes), air with moisture gets inside. The old filter is already saturated and will not be able to work effectively again, which will lead to the formation of an ice plug in the capillary or corrosion of the compressor.
What is the danger of solder getting inside the tube?
Molten solder that has flowed inside the pipe can freeze in the form of a sagging or drop. At narrowing points, such as the entrance to the capillary tube or the filter itself, this excess will block the flow of refrigerant. This will cause the refrigerator to stop freezing and the compressor to wear out. That is why, when soldering, the tubes are often held tilted down or purged with nitrogen.