Repair of a refrigeration unit associated with a violation of the tightness of the circuit requires from the master not only theoretical knowledge, but also honed practical skills working with metal. Soldering tubes is a critically important stage in restoring the functionality of equipment, since it is the quality of the seam that determines the durability of the entire system. Errors at this stage can lead to repeated refrigerant leaks, moisture entering the circuit and, as a result, expensive compressor repairs.
Unlike welding, soldering does not involve melting the base metal, but connects parts by melting a material with a lower melting point - solder. Refrigeration equipment is characterized by the use of dissimilar metals: copper-copper or copper-steel, which dictates its own requirements for temperature and the choice of consumables. A correctly executed joint can withstand high internal pressure and vibrations that occur during engine operation.
Before proceeding, it is necessary to prepare the workplace by ensuring good ventilation, since the process of heating the metal is often accompanied by the release of harmful vapors from fluxes and oxides. Hard solderused for highly loaded units, requires a more serious approach than soft tin alloys used in electronics. Understanding the physics of the process and the chemical reactions that occur during heating will help to avoid defects.
Necessary tools and consumables
The quality of the connection directly depends on the equipment used. The main tool is a gas burner running on a propane-butane mixture or acetylene. A portable torch will suffice for small diameter copper tubing, but steel compressor tubes may require a more powerful heat source that can heat the metal red hot. It is important that the flame is adjustable, allowing you to switch between heating and reducing mode.
The second key component is solder. In refrigeration technology, solid silver or copper-phosphorus alloys are predominantly used. Copper-phosphorus solder (for example BCuP) is excellent for joining copper to copper, having self-fluxing properties, but is categorically not recommended for soldering steel due to the formation of brittle joints. For copper-steel pairs, it is necessary to use silver solders with a silver content of 5% to 45% and the use of active flux.
Do not forget about auxiliary tools, without which high-quality work is impossible. The tube cutter provides a perpendicular cut without burrs, and a rimmer or needle file is needed for chamfering and cleaning edges. To form a connection, a pipe expander is often required to create a reliable fit of one pipe into another without the use of fittings, which reduces the number of potential leak points.
⚠️ Attention: The use of lead-tin soft solders in refrigerator circuits is unacceptable! They cannot withstand the pressure of modern refrigerants and temperature loads, which will lead to rupture of the seam in the first hours of operation.
Safety during work
Working with open fire and gas under pressure requires strict adherence to safety rules. First of all, you need to make sure that there are no gas leaks from the cylinder and burner hoses. The test can be done with a soap solution, applying it to the connections and observing the appearance of bubbles. The work area must be free of flammable materials, and there must be a fire extinguisher in close proximity.
Personal protection of the worker also plays an important role. It is imperative to use heat-resistant gloves that will protect your hands not only from burns, but also from accidental cuts from sharp edges of pipes. Safety glasses necessary to prevent sparks or splashes of molten flux from getting into the eyes, which can lead to serious injuries to the cornea.
Particular attention should be paid to room ventilation. When fluxes are heated and metal oxidizes, toxic substances are released. Working in a confined space without an exhaust hood or an open window can lead to poisoning. If the repair is carried out in the kitchen where the refrigerator is installed, it is recommended to temporarily dismantle the unit outside or into the garage for soldering work.
Preparing pipes for soldering: stripping and cutting
The success of soldering depends 80% on the quality of surface preparation. The metal must be perfectly clean, free of oxides, oil, dirt and moisture. Copper tubes are cleaned using a special brush or abrasive sponge until a characteristic metallic shine appears. Steel compressor pipes are cleaned with a file or coarse sandpaper.
The geometry of the connection also matters. The pipe should fit into the socket or fitting with minimal clearance, but without excessive tension. The optimal gap is 0.05–0.1 mm. If a butt joint is used (which is not recommended for refrigeration systems), the edges must be perfectly straight. To create a high-quality overlap joint, a pipe expander is often used, heating the end of the pipe and inserting a punch of the appropriate diameter into it.
After mechanical cleaning, it is recommended to degrease the surfaces with a solvent or alcohol. This will remove any remaining oil that may have gotten onto the tubes during transportation or installation. The fatty film prevents the solder from spreading and can cause seam defects, known as unsoldered joints.
☑️ Preparation for soldering
Soldering process: step-by-step instructions
The soldering process begins with heating the connection. The burner flame should be directed not directly at the joint, but at adjacent sections of the pipes to ensure uniform heating. Sudden heating of just the connection point can lead to burning through the thin-walled copper tube. The melting point of copper-phosphorus solders is about 700–750°C, silver - from 600 to 800°C depending on the brand.
When the metal reaches operating temperature, a solder rod is brought to the joint. The solder itself should not be heated with a flame - it should melt from the heat of the heated pipes. If the solder melts and immediately flows into the gap under the action of capillary forces, then the temperature is selected correctly. If the solder flows down in drops without flowing inside, it means that the pipe is not heated up enough.
After filling the seam, it is necessary to allow the joint to cool naturally. Forced cooling water or compressed air is prohibited, since a sharp temperature change creates thermal stresses in the metal, which can lead to microcracks. The cooled seam should have a smooth, uniform surface without cavities and sagging.
| Type of connection | Pipe material | Type of solder | Is it necessary flux |
|---|---|---|---|
| Copper - Copper | Cu - Cu | Copper-phosphorus | No (self-flux) |
| Copper - Steel | Cu - Fe | Silver (Ag) | Required |
| Brass - Copper | CuZn - Cu | Silver / Brass | Desirable |
| Aluminum - Copper | Al - Cu | Special. alloy for Al | Special. flux |
⚠️ Attention: When soldering an already installed refrigerator, when oil may remain in the system, heating must be carried out extremely carefully. The oil in the pipes may boil and throw a flame out of the open end of the pipe. Always keep the open end of the pipe clamped or pointed in a safe direction.
Typical errors and how to eliminate them
One of the most common errors is overheating of the connection. If the temperature is too high, the flux burns out, ceasing to perform its protective function, and the copper actively oxidizes, forming slag inside the pipe. This slag can subsequently clog the capillary tube or filter drier, causing compressor failure. A sign of overheating is blackening of copper and the presence of scales.
Underheating leads to the fact that the solder does not flow into the gap, but simply sticks to the surface, forming a “cold solder”. Such a connection is not airtight and is destroyed at the first vibration. Visually, the seam turns out matte, grainy and uneven. This can only be corrected by completely heating the assembly and adding a new portion of solder, having previously removed the old one.
Using an excessive amount of flux is also a mistake. Excess flux flowing inside the pipe forms an aggressive acidic environment, which over time corrodes the metal from the inside, causing corrosion. Flux should be applied in a thin layer only to the outer surfaces of the joint.
What to do if the solder does not flow?
If the solder does not melt when the pipe is clearly heated, you may be using the wrong type of solder for the given burner temperature, or the metal is oxidized. Try adding a little fresh flux and increasing the flame, but do not keep the burner at one point for too long so as not to burn the pipe.
Quality control and leak testing
After the seam has cooled, a visual inspection must be carried out. A high-quality solder seam should be smooth, with a slight metallic sheen (for silver solders) or a dark red tint (for copper-phosphorus solders). The presence of cracks, cavities, pores or lack of fusion indicates a defect. Such areas must be cut out and re-soldered.
However, visual inspection does not provide a 100% guarantee of tightness. A mandatory step is pressure testing the system with nitrogen. After soldering all connections, the circuit is filled with nitrogen under pressure (usually 10–15 atmospheres for household refrigerators). The pressure gauge should not show a drop in pressure within 12–24 hours.
To search for microscopic leaks that are not visible to the eye, the soldering areas are generously lubricated with soapy water or special foam. The appearance of even a small bubble indicates a violation of the seal. In this case, the nitrogen is released, and the defective area is resoldered.
Is it possible to solder refrigerator tubes with tin?
The use of soft tin-lead solders (PLS) in high-pressure refrigeration systems is not recommended and is often prohibited by manufacturers' instructions. These solders have a low melting point and insufficient mechanical strength. Compressor vibration can loosen such a seam, and high refrigerant pressure (especially in modern systems) can squeeze solder out of the gap, which will lead to leakage.
How to replace nitrogen for crimping?
In professional repairs, only dry nitrogen is used. The use of oxygen is strictly prohibited due to the risk of explosive combustion of the oil in the system. Compressed air from the compressor contains moisture, which will ruin the system, so its use is possible only in extreme cases, followed by very long vacuumization, but this does not provide a guarantee of quality.
Why do you need to keep the pipe open when soldering?
If you are soldering a pipe that is part of a closed circuit, the pressure of residual gas or vapor in it will increase sharply when heated refrigerant. This may cause a popping noise or hot oil to escape. Always ensure that expanding air or gas escapes from the pipe during soldering, if the system is not evacuated.