Repair of the refrigeration circuit is one of the most critical operations, requiring not only theoretical knowledge, but also the correct selection of materials. Tightness of connections is a critical parameter on which the service life of the compressor and the efficiency of the entire system depend. Any microcrack or poor-quality seam will lead to refrigerant leakage and moisture entering the circuit.
The question of how to solder tubes in a refrigerator does not have a universal answer, since modern units are assembled from different alloys. Copper, aluminum i Steel require fundamentally different approaches to heating and selection of filler materials. A mistake in choosing a solder can cost you repeated repairs or failure of expensive equipment.
In this article we will analyze the physical and chemical properties of various types of solders, consider the features of working with fluxes and determine the optimal one tools for the home handyman. You will learn why melting point plays a key role and how to avoid metal oxidation during the soldering process.
Physico-chemical requirements for connections in the refrigeration circuit
The refrigeration circuit operates under extreme conditions: high pressure, temperature changes from sub-zero values to heating of the compressor, as well as constant vibration impact Tensile strength and the ability to withstand cyclic loads are the main criteria for choosing a material. The connection should not crack when the tubes cool or expand.
The second critical factor is chemical inertness. A refrigerant and special oil circulate inside the system, which should not react with the seam material. If you use the wrong alloy, corrosion may begin from the inside, which will lead to the formation of plugs in the capillary tube or filter drier.
Why can't you use regular tin solder?
Tin-lead solders (TPS) have a low melting point, but insufficient mechanical strength for high-pressure sections of the refrigerator. In addition, lead can react with some types of modern oils and refrigerants, forming an acidic environment that destroys copper from the inside.
Thermal conductivity is also important to consider. The seam must quickly release heat during soldering so as not to overheat the adjacent sections of the tube, but at the same time ensure uniform temperature distribution in the joint area. Capillary effect allows solder to flow into the gap between the pipe and the fitting, creating a monolithic structure.
Classification of solders: solid and soft alloys
All materials for soldering are divided into two large groups: soft (melting point up to 450°C) and hard (above 450°C). For refrigeration equipment, in the vast majority of cases, it is hard solders, often called silver, that are used. They provide the necessary strength and tightness.
Soft solders based on tin and lead in the industrial repair of refrigerators are practically not used for the main circuit. Their use is only acceptable in low-temperature areas or for temporary sealing, but professionals avoid such solutions due to the risk of weld failure under pressure.
Silver solders can contain varying amounts of silver, copper, zinc and sometimes cadmium. The higher the silver content, the higher the ductility of the weld and its resistance to vibration. However, such materials are more expensive and require a higher heating temperature.
Specifics of copper-phosphorus solders for copper
The most common solution for joining copper tubes is copper-phosphorus solders (for example, grades BCuP or domestic analogues). Their main advantage is that there is no need for external flux when soldering copper to copper. The phosphorus contained in the alloy acts as an active reducing agent, removing oxides from the surface.
The melting point of such solders is about 700–750°C. This allows you to create reliable connections that can withstand high pressure. However, copper-phosphorus alloys have a serious drawback: they form brittle joints when in contact with ferrous metals (steel) or brass.
If you are soldering copper to steel (for example, a compressor discharge pipe), the use of pure copper-phosphorus solder is prohibited. Iron carbide forms at the contact point, which makes the weld brittle. For such assemblies, special silver solders with the addition of zinc or nickel are required.
Silver solders for dissimilar metals
When the question arises of how to solder tubes in a refrigerator, if different metals are connected (copper-steel, copper-brass), silver solders are the only right solution. They have excellent adhesion to various metals and high ductility.
The silver content in such alloys varies from 5% to 45%. For household repairs, solders with a silver content of 15–25% are considered the best choice. They have good fluidity and fill gaps even with complex spatial orientation of the tubes.
| Solder grade | Ag content (%) | Melting point (°C) | Application |
|---|---|---|---|
| PSR-15 | 15 | 645–815 | Copper, brass, steel |
| PSR-25 | 25 | 605–725 | Highly loaded units |
| BCuP-5 | 0 (copper-phosphorus) | 640–815 | Only copper-copper |
| Castolin 192 | 2 (special alloy) | 660–720 | Universal (with flux) |
The use of silver solders requires the mandatory use of flux, since they do not have self-fluxing properties, unlike copper-phosphorus analogues. The quality of surface preparation and the correct heating temperature play a decisive role here.
The role of fluxes and protection against oxidation
Flux is a chemical substance that cleans the metal surface of oxides and prevents their re-formation when heated. Without a high-quality flux, the solder will not spread over the surface, but will gather into a ball, not providing a tight seal. High-temperature fluxes are used for hard soldering.
Modern fluxes for soldering refrigeration tubes are often available in powder or paste form. They should be applied in a thin layer immediately before heating. It is important to ensure that the flux does not get inside the tube, as its remains can clog the capillary system.
⚠️ Attention: Never use acidic fluxes to solder the refrigeration circuit! Residual acid will cause rapid corrosion of copper from the inside, which will lead to the formation of copper sulfate and failure of the compressor in a few months.
When soldering with copper-phosphorus solders, flux is not necessary if clean copper surfaces are connected. However, when working with dirty or oxidized tubes, the use of flux will improve the quality of solder flow into the gap. Always remove residual flux after the seam has cooled.
☑️ Checking readiness for soldering
Tools for heating: burners and their features
For melting hard solders Temperatures above 600°C are required, so conventional soldering irons are ineffective here. The master's main tool is a gas burner. The choice of a specific type of burner depends on the amount of work and conditions of access to the tubes.
The most popular burners are for household propane-butane or MAP gas (methyl acetylene-allylene-propane). MAP gas burns at a higher temperature, which speeds up the heating process, but requires care not to burn through the thin wall of the tube. Oxy-acetylene torches produce the highest temperature, but they are bulky and dangerous for residential use.
The key point is the size of the flame. It should be soft, restorative (the inner cone is blue), without soot. The flame is not directed directly at the solder, but heats the tube itself so that the solder melts from the heat of the metal, and not from the fire of the burner.
⚠️ Attention: When working with open fire near the insulation of the refrigerator, be sure to use a screen made of tin or asbestos sheet. Thermal insulation is highly flammable, and the plastic elements hidden inside can melt.
There are also compact electric pipe soldering irons that operate on the principle of enveloping heating. They are safer than open fire, but require an electrical outlet and more time to warm up thick tubes.
Technological process of soldering: step-by-step instructions
The soldering process begins with mechanical preparation. The tubes must be cut with a special pipe cutter so as not to crush the edge, and cleaned with a brush or fine sandpaper to a metallic shine. There should be no oxides, grease or dirt on the surface.
Next, the tubes are inserted into one another. The seating depth should be no less than the diameter of the tube, but not too deep so as not to block the passage of the refrigerant. The gap between the walls should be minimal (0.05–0.2 mm) for the droplet effect to operate.
Procedure:1. Clean the surfaces.
2. Apply flux (if required).
3. Heat the connection evenly with a burner.
4. Touch the hot tube with solder (not flame!).
5. Wait for the solder to flow in a circle.
6. Cool naturally.
Heating should be carried out evenly, moving the flame around the joint. When the metal reaches the desired temperature, the solder will flow into the gap. There is no need to heat the solder bar itself - it should melt upon contact with the hot pipe.
Typical errors and ways to eliminate them
One of the most common errors is insufficient heating. The master sees that the solder is melting from the flame and tries to push it into the joint. The result is "cold soldering": the solder lies on top, but does not fuse with the base metal. Such a connection will leak at the first increase in pressure.
The second mistake is overheating. If the temperature is too high, the flux burns out prematurely, ceasing to protect the metal, and the solder itself may lose its alloying properties. In addition, the thin wall of the copper tube can simply burn out.
- 🔥 Using an open flame without a fireproof screen next to the plastic parts of the refrigerator.
- 🔥 Lack of nitrogen purge when soldering inside the circuit (leads to the formation of oxide sludge inside).
- 🔥 Trying to solder under pressure or with residual moisture in the tubes.
- 🔥 Using solder that has expired or was improperly stored.
Nitrogen purge is also often forgotten. When soldering, scale forms inside the tube, which subsequently clogs the filter drier. Professionals pass a weak stream of nitrogen through the system during soldering, displacing oxygen.
Is it possible to solder aluminum tubes with regular solder?
Aluminum requires special high-temperature solders based on zinc or aluminum and active fluxes that destroy the oxide film. Conventional copper solders do not bond to aluminum. For amateur repairs, this is a difficult task, often requiring replacing the section with copper through adapters.
Is it necessary to vacuum the system after soldering?
Yes, definitely. After any soldering, air and moisture enter the circuit. Evacuation removes moisture (by boiling at low pressure) and tests the system for leaks. Without this step, the refrigerator will not work for a long time.
What is the optimal gap for soldering a copper tube in the sleeve?
The optimal gap is 0.05–0.2 mm. If the gap is larger, the capillary effect will not work and the solder will not flow deep. If the tubes fit too tightly, there will be no room left for the solder to form a seam.