How to solder a refrigerator tube: selection of materials and technology

The appearance of an oily stain on the floor or a characteristic hissing often indicates depressurization of the circuit, and the technician is faced with an urgent question: how to solder the refrigerator tube in order to restore the functionality of the unit? The refrigeration circuit is under constant pressure, and the circulating refrigerant has a high penetrating ability, so the requirements for the quality of the seam here are much higher than with conventional plumbing repairs. An error in choosing a material or a violation of technology will lead to repeated leakage, moisture entering the system and expensive repair of the compressor.

To successfully restore the tightness, it is necessary to clearly understand what metal the damaged areas are made of, since copper, aluminum and steel require fundamentally different approaches to soldering. In modern household refrigerators, copper is most often used, but in older models or in the foamed part of the circuit, steel and even aluminum can be found. Melting point solder and flux activity must strictly correspond to the physical and chemical properties of the metals being joined, otherwise the seam will turn out brittle or leaky.

In this article we will analyze in detail what types of solders and fluxes exist, how to prepare the damaged area and what sequence of actions will ensure a long-lasting result. You will learn why you can't use regular tin-lead solder for high-temperature areas and what tools are required to work with refrigeration tubes. The correct selection of components is 80% of the success of the repair, the rest depends on the accuracy of execution.

Determination of the tube material and type of damage

The first step before purchasing consumables is to accurately identify the metal of the damaged tube. Copper is easily distinguished by its characteristic reddish tint and lack of magnetic properties; it is ductile and can be easily soldered. Steel tubes, often found in the condenser grille (the "heat lock" on the back wall), are silver or black in color, are magnetic and require more aggressive fluxes and high-temperature solders.

Aluminum tubes, which can be found in some evaporator models, are the most difficult to repair at home. In air, aluminum is instantly covered with an oxide film, which prevents solder from spreading, so to work with it you need special highly active fluxes or argon arc welding. If you are not confident in your skills working with aluminum, it is better to consider replacing the entire assembly.

⚠️ Attention: Before starting any soldering work, be sure to ensure that the refrigerant is completely vented in a well-ventilated area. Heating tubes filled with freon can lead to explosive concentrations of gases or the formation of toxic compounds.

The type of damage also dictates the choice of method. Microcracks and pig holes caused by corrosion require careful cleaning and, possibly, installation of a patch made of the same metal. Mechanical breakdowns or fractures of tubes after transportation are usually eliminated end-to-end using a coupling or the pipe-to-pipe method.

Selection of solder: hard and soft alloys

The main criterion for choosing solder is the melting point and strength of the connection. For refrigeration systems, solders are traditionally divided into two large groups: soft (tin-lead and their analogues) and hard (silver, copper-phosphorus, copper-zinc). Soft solders melt at temperatures up to 450°C and are used primarily for low-temperature areas or repair of aluminum parts with special compounds.

However, for the main circuit, where pressure and vibration are high, experts recommend the use of hard solders containing silver (Ag). Silver solder provides excellent fluidity, high tensile strength and resistance to vibration loads of the compressor. The silver content in the alloy can vary from 5% to 45%: the higher the percentage, the more elastic and stronger the seam, but the higher its cost.

Copper-phosphorus solders (for example, brand PhosCopper) are ideal for soldering copper to copper, so how phosphorus plays the role of a reducing agent and does not require the use of flux. But they absolutely cannot be used to connect copper to steel, since the resulting iron phosphide makes the seam extremely brittle and brittle. For copper-steel pairs, silver solder with the obligatory use of flux is required.

The table below provides a comparison of the main types of solders used in the repair of refrigeration equipment:

Necessity and types of fluxes

Flux is a chemical substance designed to clean the surface of a metal from oxides and prevent their formation during the heating process. Without a high-quality flux, the solder will not “spread” over the metal, but will gather into a ball without ensuring a tight seal. For soldering refrigeration tubes, using the correct flux is as important as choosing the solder itself.

For copper-phosphorus solders, flux is usually not required, since phosphorus itself reduces copper oxides. However, when soldering copper to steel or using silver solders, the use of flux is mandatory. The most popular are paste-like fluxes, which are convenient to apply with a brush, and liquid formulations in bottles. It is important to choose fluxes specifically designed for refrigeration equipment and air conditioning, since they do not contain chlorides that cause corrosion.

Flux residues after soldering are an aggressive environment and can corrode metal or wire insulation over time if located near electrical equipment. Therefore, after the seam has cooled, it is necessary to carefully remove chemical residues with warm water and a brush or special solvents, if the instructions for the flux allow this. Some modern fluxes are labeled as “no rinsing,” but in a closed refrigerator circuit it’s better to be on the safe side.

Why can’t you use rosin?

Ordinary rosin used in radio engineering has insufficient activity for cleaning oxides on steel tubes at high temperatures. In addition, the products of its combustion can coke the capillary tube if they get inside the system, which will lead to blockage and failure of the compressor.

Preparation of tools and workplace

The quality of soldering directly depends on the preparation. You will need a gas torch with a narrow flame to locally heat the joint without melting adjacent plastic parts or insulation. For domestic purposes, compact burners for household propane-butane or more powerful options for MAP gas, which give a higher temperature, are excellent.

To clean pipes, use fine sandpaper (zero) or special pipe cleaners. The surface must be perfectly clean and matte. Also have tweezers or pliers ready to hold the solder so you don't burn your fingers, and a damp rag to cool the surrounding areas. Don't forget about personal protective equipment: gloves and goggles are required.

If you have to solder in a hard-to-reach place, near plastic housing elements or insulation, be sure to use heat sink clamps or just a damp rag wrapped around the tube below the soldering point. This will prevent solder from flowing down the tube and melting the plastic.

Technology for soldering copper and steel pipes

The soldering process begins with thoroughly cleaning the ends of the pipes. Remove the oxidized layer until a bright metallic sheen appears in an area larger than the area of ​​the future connection. Apply a thin layer of flux to both surfaces to be joined. If you use copper-phosphorus solder for copper, this step can be skipped, but for steel, flux is required.

Heat evenly, moving the burner flame around the joint. Do not keep the flame at one point so as not to burn through the thin wall of the tube. Once the metal is at the desired temperature (usually cherry red for steel or dark red for copper), bring the solder rod to the joint. The solder should melt from the heat of the metal, and not from the flame of the torch, and be drawn into the gap by capillary effect.

⚠️ Attention: Never direct a stream of hot air or flame into the tube for a long time. This can cause oxidation of the inner surface and the formation of “flakes”, which will subsequently clog the capillary or filter drier.

After the solder has filled the joint, remove the torch and allow the seam to cool naturally. Do not blow on the seam or forcefully cool it with water - a sharp temperature change can cause microcracks in the crystal lattice of the metal, which will lead to loss of tightness under pressure. The cooled seam should be smooth, without cavities or sagging.

Features of soldering aluminum elements

Soldering of aluminum is a more complex process due to the quickly formed oxide film. For this purpose, special solders based on zinc or aluminum with silicon and highly active fluxes are used. The technology requires quick action: after applying flux and heating, the soldering area must be actively rubbed with a solder rod in order to destroy the oxide film mechanically at the time of the chemical reaction.

The temperature regime is critical here: aluminum does not change color when heated, like steel, and can easily flow, turning into a shapeless mass. Use thermal markers (pencils) that melt when the desired temperature is reached to control the heat. For critical evaporator assemblies, it is often recommended to use the “cold welding” method (two-component epoxy compounds for low temperatures) or replacement of the assembly, since the solder seam on aluminum is less reliable during vibration.

If you use gas-melt solder for aluminum (for example, in the form of a wire with a flux core), the technique is similar to copper soldering, but requires more intensive mixing of the contact zone. Make sure that the flux completely covers the soldering area, isolating it from oxygen.

Is it possible to solder a hole in an aluminum evaporator with tin?

There are special high-temperature tin solders for aluminum, but they require very careful surface preparation (often using copper sulfate for galvanic copper deposition) and do not guarantee durability in conditions of constant vibration and temperature changes.

Checking tightness and completing work

After the seam has cooled and removed flux residues, it is necessary to check the quality of work. Visual inspection is not always indicative, so professionals use the nitrogen pressure test method. However, at home you can use a soap solution. Lather the soldering area and adjacent areas generously. If bubbles appear, the tightness is broken, the procedure must be repeated.

Remember that after soldering and restoring the tightness, the system must be evacuated. When the compressor operates, the moisture and air remaining inside will turn into acid and ice, which will kill the refrigerator in a few months. Evacuation removes moisture and air, creating conditions for the correct operation of the refrigerant.

The final stage is filling the refrigerator with freon. The amount of refrigerant and its brand are indicated on a technical sticker, usually located inside the chamber or on the back wall. Overfilling or underfilling freon will lead to incorrect operation of the unit, so use a scale or a pressure gauge station for precise dosage.

Which solder is best for a beginner to choose for a copper tube?

For a beginner, the best option would be copper-phosphorus solder (for example, with a phosphorus content of 6-8% and silver 2-5%). It does not require flux when soldering copper to copper, has good fluidity and forgives small errors in heating temperature. Avoid pure tin for main lines.

Is it necessary to strip the inside of the tube?

It is mechanically impossible and unnecessary to strip the inner surface. The main thing is to prevent scale, flux or solder from getting there. When soldering, hold the tube with the hole facing down so that gravity prevents contaminants from flowing inside. Blowing with nitrogen during soldering (if possible) helps blow out possible scale.

What to do if the solder does not stick to the tube?

Most likely, the surface is not sufficiently cleaned, heated, or the wrong flux is used. Make sure the metal is shiny, the flux is active (not dry), and the tube is hot enough to melt the solder. Try adding a little fresh flux and increasing the heat, but without fanaticism, so as not to burn the metal.

Is it possible to solder a refrigerator without pumping out freon?

Absolutely not. Soldering should only be done after the refrigerant has been completely removed from the circuit. The presence of gas inside will create excess pressure, which will blow out the molten solder, and heating the gas can cause the oil to ignite or explode. In addition, freon combustion products are toxic.