The situation when an oily stain appears on the floor under the refrigerator, and the cold suddenly disappears inside the chamber, is familiar to many owners of household appliances. This is a sure sign that the tightness of the circuit is broken and the refrigerant has left the system. Often the cause is a microscopic crack in the copper tube or a leak in the soldering area, which requires immediate attention. If you decide not to call a technician, but to carry out the repair yourself, you will be faced with the soldering process, which is a fundamental skill for restoring the functionality of the unit.
Soldering refrigerator tubes is not just connecting two pieces of metal, but creating a reliable, sealed seam that can withstand high pressure and vibration of the compressor for many years. Errors at this stage can lead to repeated leaks, moisture entering the system and, as a result, expensive compressor repairs. In this article, we will analyze in detail all the nuances of working with copper and steel, choosing the right consumables and the technology for creating an ideal connection that will last for many years.
Preparation of the workplace and necessary tools
Before you start heating the metal, you need to organize a safe space. Soldering involves the use of open flame and high temperatures, so good ventilation is a must. The workplace should be free of flammable objects, and a fire extinguisher or a container of water should always be at hand in case of unforeseen situations.
The main tool for work will be a burner. For domestic needs, a propane-oxygen or propane-air burner is ideal, which provides a flame temperature of up to 1500 degrees Celsius. Gas cartridges with disposable burners often do not provide enough power to heat the thick walls of the tubes, especially when it comes to the junction of copper and steel. You will also need a pipe cutting kit, a rolling tool and, of course, personal protective equipment.
⚠️ Attention: When working with an open flame in a confined space, there is a risk of a decrease in oxygen levels and accumulation of combustion products. Always provide a supply of fresh air.
Don't forget to prepare clean rags and flux. A clean surface is the key to a high-quality seam, and any contamination can negate all efforts. The tools must be in good working order, and the gas supply hoses must not have cracks or damage through which leakage may occur.
The choice of solder and flux for different metals
The quality of soldering directly depends on the correct choice of consumables. Refrigeration systems use different metals, most often copper and steel, less often aluminum. Each combination requires a different approach and a different type of solder. Using an unsuitable alloy will result in the seam being brittle or leaking due to temperature changes.
For connecting copper tubes to each other, phosphorus-containing soldersis most often used. Their main advantage is that they do not require the use of additional flux, since phosphorus itself acts as an oxide reducer. Such alloys have a melting point of about 700-750 degrees and provide a strong, elastic connection. However, they absolutely cannot be used for soldering steel or cast iron, since brittle iron phosphides are formed.
Why can’t you solder steel with silver-containing solder without flux?
Silver solders without phosphorus do not have self-fluxing properties. When you try to join steel without flux with them, the solder will simply roll into a ball and will not spread along the seam, since the oxide film on the steel will not be destroyed.
For a copper-steel joint, which is often found at the point where the tube exits the compressor or in a condenser, it is necessary silver-containing solder with a silver content of 15% to 45%. Unlike copper-phosphorus alloys, the use of flux is mandatory here. The flux cleans the surface of the metal from oxides and improves the fluidity of the molten metal, allowing it to penetrate into the smallest gaps by capillary effect.
- 🔥 Copper-phosphorus solder - ideal for soldering pure copper, does not require flux, has good fluidity.
- 💎 Silver solder (BCuP or analogue) - used for critical connections and dissimilar metals, requires flux.
- 🛢️ Flux paste - necessary for steel parts, prevents oxidation and improves solder adhesion.
- 🚫 Tin-lead solder is NOT suitable for refrigerators, as it has a low melting point and cannot withstand pressure.
When choosing a flux, pay attention to its temperature range of activity. It should start working a little before the solder melts and remain active throughout the process. Remains of flux after soldering must be removed with warm water or a special solvent, as they can cause corrosion of the metal over time.
Technology for soldering copper tubes: a step-by-step algorithm
The process of joining copper elements is a basic skill with which to begin mastering the craft. The main rule here is uniform heating. Do not direct the flame only to the solder or only to one of the tubes; The entire assembly must heat up so that the metal reaches operating temperature at the same time.
First, it is necessary to clean the ends of the tubes from burrs and oxides. Use a special brush or fine-grained sandpaper for this. The surface should be shiny and clean. Then one tube is inserted into the other, maintaining a gap. The optimal gap for capillary soldering is from 0.05 to 0.2 mm. If the gap is too large, the solder will not flow into the joint.
☑️ Checklist before soldering
Heat with a medium-hard flame, moving the burner around the joint. Do not keep the fire at one point so as not to burn through the thin walls of the tube. When the metal is heated to the desired temperature (about 700 degrees, the copper will turn a dark cherry color), bring the solder rod to the joint. The solder should melt from the heat of the tubes, and not from direct contact with the burner flame.
As soon as the solder touches the heated metal, it will begin to actively flow into the gap under the influence of droplet forces. At this point, you need to remove the burner and let the seam cool naturally. Do not blow on the seam or cool it with water, as sudden cooling can lead to the formation of microcracks in the metal structure.
| Type of connection | Soldering temperature | Type of solder | Do you need flux |
|---|---|---|---|
| Copper - Copper | 700-750 °C | Copper-phosphorus | No |
| Copper - Brass | 750-800 °C | Silver | Yes |
| Copper - Steel | 800-850 °C | Silver (high Ag) | Yes |
| Steel - Steel | 850-900 °C | Copper-zinc | Yes |
It is important to monitor the amount of solder added. Its excess can lead to the formation of internal deposits, which narrow the flow area of the tube and create additional resistance to the refrigerant flow. This is especially critical for thin capillary tubes.
Soldering of dissimilar metals: copper and steel
Joining copper and steel tube is the most difficult step encountered when repairing refrigerators. The problem lies in the different thermal conductivity and melting point of these metals. Copper removes heat much faster than steel, so if heated evenly, the steel can overheat and burn out before the copper reaches the desired temperature.
To solve this problem, experienced craftsmen use the offset heating technique. The torch flame is directed primarily at the steel piece, allowing heat to be transferred to the copper through conduction. Visually monitoring the temperature has become more difficult, since it does not change color as clearly as copper. It is important here not to overheat the joint.
⚠️ Attention: When exposed to strong heat, steel burns out (oxidizes) from the inside. If you see that the metal begins to “boil” or sparks appear, the temperature must be lowered immediately.
For such connections it is critical to use flux, specially designed for steel soldering. Regular copper flux may not cope with the oxide film on steel. The solder must have a high silver content, which ensures the necessary plasticity of the seam and compensates for the difference in the linear expansion coefficients of the metals.
The process looks like this: apply flux to both surfaces, insert a copper tube into a steel one (or vice versa, depending on the design), heat the joint, shifting the flame towards the steel. When the flux becomes transparent and liquid, add solder. It should envelop the joint on all sides.
After cooling, the seam must be thoroughly cleaned of flux residues. Aggressive flux components can destroy the thin wall of a steel tube in a short time, causing a new leak. Rinse the soldering area with warm water using a brush until the chemicals are completely removed.
Fixing leaks and working with the condenser
Often the need for soldering arises when a leak is detected in the evaporator or condenser. If the damage is in an accessible area of the copper tube, it can be soldered. However, if we are talking about a foamed evaporator inside the refrigerator body, the technology changes. In such cases, it is often necessary to cut out the damaged area and weld a new one, or completely change the assembly.
Before soldering, the leak site must be thoroughly cleaned. If the hole is small, you can temporarily plug it with a piece of solder and then heat it to make a full connection. When working with aluminum evaporators (which are found in older models), conventional brazing is impossible without special fluxes that destroy the oxide film or the use of argon welding.
- 🔍 Find the exact location of the leak using a soap solution or a leak detector.
- 🧹 Clean the surface around the hole to pure metal.
- 🔥 Warm up the area, being careful not to damage the adjacent turns of the capacitor.
- 🔩 Apply a copper foil patch or apply solder directly into the hole.
When replacing the capacitor (grid at the back of the refrigerator), it is important to maintain the length and diameter of the tubes of the new coil. A capacitor that is too long or short will upset the balance of the system, causing the refrigerator to not operate properly. Soldering of new connections is carried out according to the standard scheme: copper-copper or copper-steel.
After completing all soldering work, the system must be purged with nitrogen. This will remove flux residues, oxides and possible moisture that got inside the tubes during repairs. Only after purging and evacuation can the system be charged with freon.
Typical errors and safety measures
Even experienced craftsmen make mistakes that can cost the functionality of the refrigerator. One of the most common is overheating of the soldering area. Excessive temperature causes scale to form inside the tube, which then clogs the filter drier or capillary tube. This causes an increase in pressure and failure of the compressor.
Another error is insufficient heating. If you apply solder to cold metal, it will simply stick to the outside, but will not flow into the joint. Such a seam may visually appear intact, but at the first start and increase in pressure, the tightness will be broken. Always wait until the metal itself melts the solder.
Do not forget about safety. Freon leaving the system at high temperatures can decompose to form toxic phosgene. Therefore, you need to solder only after the refrigerant has been completely removed from the circuit. Work in a ventilated area and use a respirator when working with fluxes.
It is also worth mentioning the risk of fire insulation. Before starting work, be sure to remove the foam insulation from the pipes in the heating area to a distance of at least 15-20 cm in both directions. The insulation is easily ignited by a spark or accidental contact with a flame.
Is it possible to solder tubes without nitrogen?
Technically it is possible, but not recommended. Soldering without nitrogen purging results in the formation of copper oxides inside the tubes. These oxides clog the system over time, reducing cooling efficiency and increasing the load on the compressor.
Which solder is best for a beginner?
For beginners, copper-phosphorus solders with a silver content (for example, 5-15%) are best. They are more ductile, flow easier and forgive small errors in temperature conditions, in contrast to pure copper-phosphorus alloys.
Is it necessary to vacuum the system after soldering?
Yes, this is a mandatory step. After any soldering, air and moisture enter the system. Evacuation removes moisture, which can block the capillary when frozen, and removes air, which increases the pressure in the system.
What to do if the solder does not flow?
Most likely, the base metal is not heated up enough or the wrong flux is used. Make sure that the flame is directed towards the tube and not towards the solder rod, and that the temperature has reached the required value (the metal must be hot).