Repairing a refrigeration circuit often requires restoring the tightness of the system, and soldering copper tubes is a key skill for the master. Pipeline failure can occur due to corrosion, mechanical damage or vibration, resulting in refrigerant leakage. A high-quality connection guarantees long-term operation of the compressor and correct pressure in the system.
The process requires not only specialized equipment, but also an understanding of the physical properties of copper and solders. Copper has high thermal conductivity, so heating occurs quickly, but cooling also requires control. Errors at this stage can lead to repeated depressurization or blockage of the system with oxides.
Before starting work, it is necessary to prepare the workplace and ensure good ventilation, since the process is accompanied by the release of flux vapor. Safety is a priority, because the work is carried out with open flames and pressurized gas cylinders. A careful study of the technology will allow you to avoid common mistakes of beginners.
Necessary tools and materials for soldering
To make a high-quality connection of copper tubes of the refrigerator, a simple gas torch is not enough. You will need a set of equipment that provides precise temperature control and clean connections. The main tool is an oxy-propane or oxy-acetylene torch, which allows you to reach the melting point of the solid solders.
In addition to the fire source, the use of nitrogen is critical. Purging with nitrogen during heating prevents the formation of an oxide film inside the tube. Ignoring this step leads to the appearance of scale, which can subsequently clog the capillary tube or filter drier, causing serious damage.
- 🔥 Gas torch with a set of tips of different diameters for uniform heating.
- 🧪 Solid silver solder (containing silver from 15% to 45%) for a reliable seam.
- 🛡️ Nitrogen cylinder with a reducer to create an inert environment inside the circuit.
- ✂️ Pipe cutter and rimmer for preparing pipe edges without deformation.
The choice of solder depends on type of metals being joined. If you are soldering copper to copper, you can use phosphorus-containing solders without flux, since phosphorus acts as a reducing agent. However, when connecting copper to steel (for example, a compressor discharge tube), the use of flux and silver solder with a higher melting point is required.
⚠️ Attention: The use of soft tin-lead solder (POS) for high-pressure sections of the refrigerator circuit is unacceptable. It cannot withstand pressure and temperature loads, which will lead to rupture of the connection.
Surface preparation also plays a role. The tubes must be clean, free of traces of oil and old insulation. For cleaning, use special brushes or sandpaper, removing the oxide layer until a metallic shine appears.
Pipe preparation and safety precautions
The first step in the process is the correct preparation of the elements to be joined. The copper tube must be cut perpendicular to its axis using a pipe cutter. Using a hacksaw for metal is strictly not recommended, as small chips can get inside the system and cause fatal consequences for the compressor.
After cutting, it is necessary to remove the chamfer (with a rimmer) and clean the outer surface of one pipe and the inner surface of the other if the bell method is used. The gap between the walls of the pipes should be minimal, usually from 0.05 to 0.2 mm, so that the capillary effect can properly distribute the molten solder.
☑️ Preparation for soldering
Safety precautions when working with gas and fire require strict adherence to the rules. Cylinders must be installed vertically and secured, hoses must not have cracks. There must be a fire extinguisher in the room and the absence of flammable materials within a radius of several meters.
Particular attention should be paid to the residual refrigerant in the system. Even after bleeding, vapors may remain in the compressor oil, which when heated form an aggressive acid. Therefore, before soldering, the system is often purged with dry nitrogen.
Wear protective glasses and gloves to prevent burns from flux splashes or accidental contact with hot metal. Copper retains heat for a long time, and it can be difficult to visually identify a cooled tube.
Soldering process: step-by-step instructions
The direct soldering process begins with setting up the torch. The flame should be neutral, with a clearly defined inner cone. A too oxidizing flame (excess oxygen) will burn copper, creating deep craters, and a reducing flame (excess gas) will smoke the surface.
Heating should be done evenly, moving the flame around the pipe joint. Do not hold the torch motionless at one point, so as not to burn through the thin wall of the tube. When the copper reaches a temperature of about 600-700 degrees Celsius, it will begin to melt the solder when touched.
- 🌡️ Heat the joint evenly, moving the torch around the joint.
- 🪄 Touch the solder to the joint on the side opposite to the flame.
- 💧 Allow the molten metal to flow into the gap under the action of capillary forces.
- ❄️ Allow the joint to cool naturally without cooling with water.
If you use flux, apply a minimal amount only to the joint. Excess flux when heated can boil and throw solder out of the joint, breaking the seal. The solder should flow into the joint itself; no need to try to spread it like butter.
Why can’t you blow on cooling copper?
Forced cooling with water or air leads to a sharp temperature difference. This causes internal stress in the metal, which can lead to microcracks in the seam or the tube itself, especially at the transition from the hot to the cold section. In addition, sudden cooling can “lock” flux bubbles inside the seam, creating a hidden cavity.>
Visually, a correct joint looks smooth and shiny (after removing flux residues), without sagging or cavities. The solder should form a uniform bead along the entire perimeter of the joint.
⚠️ Attention: If the solder does not flow into the gap, but rolls up in balls, it means that the pipe temperature is insufficient or the surface is poorly cleaned. Do not add more flux, it is better to heat the joint more strongly.
After soldering is completed and cooled, it is necessary to remove the remaining flux with warm water and a brush. Aggressive flux components can cause corrosion of copper over time if they are not washed off.
Soldering with nitrogen purge: why is it necessary
Professional repair of refrigerators is impossible to imagine without the use of nitrogen purge. When copper is heated in air, it reacts vigorously with oxygen to form copper oxide (CuO). These oxides look like black flaky scale that easily peels off from the pipe walls.
Circulating through the system along with oil and refrigerant, this scale acts as an abrasive. It can get stuck in a narrow opening in a capillary tube or thermostatic valve, stopping the refrigerator from working completely. Oxides also accelerate the decomposition of oil, reducing lubricity.
The technology consists of applying a small nitrogen pressure (about 0.5-1 atmosphere) inside the pipe during soldering. The gas flow displaces oxygen from the heating zone, preventing the chemical oxidation reaction. As a result, a clean copper surface remains inside the pipe.
If you do not have the opportunity to use nitrogen (although this is highly undesirable for quality work), the risk of oxide formation becomes very high. In such cases, craftsmen sometimes try to burn out oxidized vacuum, but this does not provide a 100% guarantee of cleaning.
| Parameter | Without nitrogen | With nitrogen purge |
|---|---|---|
| Formation of oxides | High (black coating) | None or minimal |
| Risk of clogging | High | Minimum |
| Compressor service life | Decreased | Maintained |
| Oil quality | Deteriorates quickly | Remains stable |
The use of nitrogen is an industry standard that distinguishes amateur repairs from professional ones service. Neglecting this stage often leads to repeated calls and claims from clients.
Typical mistakes and how to avoid them
One of the most common errors is overheating of the connection. When copper heats up to a reddish or cherry color, it becomes brittle and can burst with the slightest mechanical stress or vibration. In addition, when overheated, the zinc from the solder burns out, making the seam porous.
Insufficient heating leads to the fact that the solder does not penetrate deep into the joint, but only sticks to the surface. Such a connection may look tight immediately after soldering, but will come apart during the first defrost cycle or vibration of the compressor.
- 🚫 Using dirty or oxidized pipes without cleaning.
- 🚫 Lack of clearance between the pipes (too tight fit).
- 🚫 Soldering under pressure (strictly prohibited).
- 🚫 Rapid cooling with water to speed up the process.
Another mistake is the wrong choice of insert length. If you insert one pipe into another too deeply, the solder may not reach the end of the joint due to an air lock. If it is too small, the contact area will not be sufficient for strength.
It is also worth mentioning the error in choosing the soldering location. Do not solder the tube close to the plastic parts of the refrigerator or to the sealed compressor casing without thermal protection. Heat can melt the plastic or damage the varnish winding of the motor inside the casing.
To protect nearby elements, use a damp cloth or special heat-protective foil shields. This will help localize the heat only in the joint area.
Checking quality and tightness
After cooling and cleaning the seam, you need to make sure that the joint is tight. A visual inspection may show obvious defects: cracks, holes or unsoldered areas. However, microscopic fistulas may not be visible.
The most reliable way to check is to pressurize the system with nitrogen. The circuit is filled with nitrogen under pressure (usually 10-15 atmospheres for household refrigerators) and left for several hours or days. A drop in pressure will indicate the presence of a leak.
If there is no pressure gauge, you can use a soap solution. Apply thick soap suds to the soldering area and watch carefully for bubbles. Even the slow inflation of a bubble indicates a microscopic hole.
If a leak is detected, it is necessary to release the pressure, cut out the defective area and resolder the connection. Attempts to solder a fistula over old solder rarely give long-term results.
⚠️ Attention: Never test the tightness with an open flame (torch) in the presence of refrigerant vapors. Some refrigerants, upon contact with a flame, form phosgene, a chemical warfare agent.
Only after successful pressure testing and evacuation can the system be charged with refrigerant. Compliance with soldering technology is the key to ensuring that the refrigerator will operate for years without the need for repeated intervention in the circuit.
Is it possible to solder copper with tin (POS-61)?
Technically possible, but highly not recommended for refrigeration circuits. Tin-lead solders have a low melting point and low mechanical strength. Compressor vibration and temperature changes can quickly destroy such a connection. In addition, lead is incompatible with some types of modern oils and refrigerants.
How to replace nitrogen when soldering?
There is no complete replacement for nitrogen to create an inert environment. Argon or helium are also inert, but nitrogen is cheaper and more accessible. Some craftsmen try to use carbon dioxide, but it can react with metals at high temperatures. Working without purging is only permissible in extreme cases and requires subsequent thorough flushing of the system.
Why does solder roll up into balls?
This happens if the temperature of the copper pipe is lower than the melting point of the solder. The copper should melt the rod itself when touched. Another reason is a contaminated surface (oil, oxides), due to which the solder cannot “wet” the metal and adhere to it.
Is it necessary to clean the pipe after soldering?
Yes, definitely. Flux residues contain active chemicals (acids), which over time can cause corrosion of the copper and the formation of fistulas. After the seam has cooled, rinse it with warm water and a neutral detergent and wipe dry.