Restoring the functionality of a refrigeration unit often requires intervention in the sealed circuit of the system. If you are faced with a refrigerant leak or the need to replace the compressor, then installing a service valve becomes a mandatory step. The Schroeder valve, often simply called service valve, allows you to repeatedly connect a pressure gauge station to diagnose pressure and refill freon without compromising the integrity of the tubes.
The soldering process requires not only special equipment, but also an understanding of the thermodynamics of the refrigeration cycle. Incorrect installation can lead to repeated leakage, contamination of the system with flux combustion products, or even failure of the new compressor. In this material, we will look in detail at how to choose the right location, prepare copper tubes and perform high-quality soldering, ensuring the long service life of your refrigerator.
Before you get started, you need to make sure that you have basic skills in working with gas soldering equipment. It is important to understand that copper becomes very plastic when heated, and excess solder can clog a thin capillary. Therefore, accuracy and compliance with temperature conditions play a decisive role here.
Preparation of tools and selection of installation location
The first step is the selection of the necessary tools and consumables. For high-quality work, you will need not only the valve itself, but also a reliable source of fire. Typically, craftsmen use a mixture of oxygen with propane or acetylene, since the flame temperature must reach 800-900 degrees Celsius to melt copper-phosphorus solders.
The place for tapping is selected based on ease of access and the type of work performed. If you are replacing a compressor, the Schrader valve is usually soldered into the discharge tube (high pressure) or process tube (low pressure) of the new motor. In case of searching for a leak or evacuation of the system, the valve is installed on the free end of the copper pipe, having previously cut off the sealed factory shank.
- 🔧 Gas burner with a set of nozzles for local heating.
- 🧪 Copper-phosphorus solder (BCuP) without silver content for copper.
- 🛡️ Safety glasses and heat-resistant gloves for safety.
- 🧹 Pipe cutter, rimmer and brush for cleaning internal surfaces.
Pay special attention to the cleanliness of the surfaces to be joined. Oxides formed during heating can cause the seam to leak. Therefore, before soldering, it is recommended to clean the outer surface of the tube and the inside of the valve fitting to a metallic shine.
⚠️ Attention: Never use brass or steel fittings for soldering directly to copper refrigerator tubes without adapters, since different coefficients of thermal expansion will lead to cracks during the first heating-cooling cycle.
Technology for soldering copper connections
The process of joining copper to copper using hard solders is based on the capillary effect. Molten metal flows into the gap between the tube and the fitting, creating a strong and airtight connection. The key point here is uniform heating of the part. If you heat only the tube, the solder will form a lump and will not flow inside.
Heat the joint with a flame evenly, moving the torch around the joint. When the copper reaches a dark red color (approximately 700°C), bring the solder rod to the joint. If the temperature is sufficient, the solder will melt from the heat of the metal, and not from direct contact with the burner flame, and will flow into the gap under the action of capillary forces.
It is important not to overheat the soldering area, since phosphorus solder it may burn out, losing its properties, and the thin wall of the tube may burn out. After the solder has flowed, remove the torch and allow the seam to cool naturally. Forced cooling with water or air is prohibited, as this creates microcracks in the metal structure.
- 🔥 Heat the joint evenly on all sides.
- 🌡️ Control the color of the copper: it should become dark cherry.
- 💧 Avoid getting solder inside the tube so as not to block the passage.
When soldering the Schrader valve, make sure that the valve is open or the cap is removed, otherwise the expanding air inside the closed volume can squeeze the solder that has not yet hardened out, breaking the tightness.
Why can’t you heat the solder itself?
It is the parts being connected that need to be heated, not the solder rod. If you heat the solder itself with a flame, it may not flow into the gap, but simply flow down or oxidize, which will lead to the formation of cavities and a poor-quality seam. Heat must be transferred from hot copper.
Use of nitrogen during soldering: why is it necessary
Professional repair of refrigerators is impossible without the use of nitrogen. When copper is heated in the presence of oxygen, copper oxide (black deposit) forms on the inner walls of the tubes. These scales are subsequently torn off by the flow of freon and oil, ending up in the filter drier or, worse, in the thinnest channels of the capillary tube.
Clogging the capillary with oxides is one of the most common reasons for repeated failure of the refrigerator after repair. To avoid this, nitrogen must be continuously purged through the system at low pressure during soldering. This displaces oxygen and prevents oxidation of the internal walls.
If you do not have a nitrogen reducer, you can use a simple method: apply gas so that you feel a slight movement of air with your hand at the exit of the other open pipe, but do not allow a strong flow that will blow away the burner flame. This minimizes the formation of scale inside the circuit.
| Parameter | Soldering without nitrogen | Soldering with nitrogen purge |
|---|---|---|
| Oxide formation | High (black plaque) | Almost absent |
| Risk of clogging | High (capillary, filter) | Minimum |
| System service life | Reduced | Maximum |
| Oil quality | Contaminated with acids | Remains clean |
Ignoring nitrogen purging is permissible only in extreme cases, when under there is no cylinder in hand, but this is always a risk for the durability of the repair. Ideally, nitrogen should be supplied before heating begins and stop only after the seam has cooled.
Installation of the valve on different types of tubes
The design of the tubes in modern and old refrigerators may differ. Older models use copper-tipped steel tubing or all-steel lines. Soldering a Schrader valve to steel requires the use of special solders with a high silver content (for example, 30% Ag) and appropriate fluxes.
In modern refrigerators, such as Indesit, Atlant or LG, an aluminum evaporator “loop” is often found. Soldering aluminum to copper (valve) is not possible using conventional methods. In such cases, special adapter bushings ("aluminum-to-copper") or mechanical connections are used, if the design allows.
If you solder the valve into a gap in a copper pipe, make sure that the diameter of the fitting matches the diameter of the pipe. Standard sizes for household refrigerators are 1/4 inch (6 mm) or 3/8 inch (9.5 mm). A discrepancy between the diameters will either lead to the impossibility of connecting or to an excessive narrowing of the flow area, which will create hydraulic resistance.
- 🔩 For steel, use silver solders and flux.
- ❄️ For aluminum, you need special adapters or argon.
- 📏 Ensure that the diameters of the pipe and the valve fitting match.
⚠️ Attention: When working with steel pipes, be sure to remove the factory copper coating (if there is one at the soldering site) and degrease the surface, otherwise the solder will not stick to the base, but only to the surface layer, which will quickly peel off under pressure.
☑️ Check before soldering
Check tightness and pressure testing
After the Schrader valve has been successfully soldered, you cannot immediately begin charging the refrigerant. The first mandatory step is to pressurize the system with nitrogen. This makes it possible to identify microscopic leaks that could have formed at the soldering site or be present in other components of the circuit.
Connect the gauge manifold to the installed valve and supply nitrogen. For household refrigerators, the pressure test is usually 10-15 atmospheres (bar). After building pressure, turn off the valve on the cylinder and monitor the pressure gauge readings for 20-30 minutes.
If the pressure gauge needle is in place, the system is sealed. If the pressure drops, you need to look for a leak. The most effective way is to use a soap solution. Apply thick foam to the valve soldering area. The appearance of bubbles will indicate a seam defect. In this case, bleed off the nitrogen, redo the soldering and repeat the procedure.
Therefore, the safety margin of the soldering must be high. Slight fluctuations in the pressure gauge needle can be caused by changes in the ambient temperature, but a sharp drop indicates a leak.
Typical mistakes and how to avoid them
Even experienced craftsmen sometimes make mistakes that ruin all the work. One of the most common is insufficient depth of the tube in the valve fitting. If the tube does not enter all the way, the contact area of the solder will be small, and under the pressure of freon the connection may depressurize.
Another common mistake is using an excessive amount of solder. It seems to beginners that the more solder, the more reliable. In fact, the excess flows inside the tube, forming sagging. These nodules create flow turbulence, noise and can come off, causing a blockage.
It is also worth mentioning the error in choosing a location. The Schrader valve should be soldered on a straight section of the pipe, at least 5-7 cm away from bends or other soldering joints. This is necessary so that the heat from the burner does not overheat adjacent connections and does not break their tightness during operation.
- 🚫 Do not heat the soldering area for too long so as not to anneal the copper.
- 🚫 Do not allow moisture to get inside the tubes before soldering.
- 🚫 Do not use rusty or oxidized valve fittings.
The quality of the work performed directly affects the life of the refrigerator. A neat, even seam without cavities and sagging is a sign of professionalism and a guarantee that the refrigerator will work for years without the need for repeated intervention.
Is it possible to solder a Schrader valve with ordinary tin solder?
The use of tin-lead solders (PLS) for high-speed refrigerators is not recommended. They have a low melting point and lower mechanical strength compared to copper-phosphorus alloys. Compressor vibration and temperature changes can destroy such a connection over time. In addition, PIC requires the use of aggressive fluxes, which are difficult to completely remove from inside the system.
Is it necessary to change the filter-drier after soldering the valve?
Yes, replacing the filter-drier is required for any opening of a sealed circuit. While you are soldering the valve, the system is in contact with air, and the sorbent in the old filter could already absorb moisture. Installing a new filter ensures that residual moisture and acids are removed from the system, protecting the compressor from insulation breakdown.
Which Schrader valve is better: brass or steel?
Brass valves are better suited for soldering to copper refrigerator tubes, since they are easier to solder with copper-phosphorus solders. Steel valves require silver solders and more careful surface preparation. However, steel options are often stronger mechanically. The main thing is the quality of the thread and the spool assembly itself.
What to do if tin leaks from an old seam during soldering?
If, when heating a nearby seam, solder leaks out of it, it means you have overheated the adjacent area. In this case, it is necessary to cool the area, clean again and re-solder the damaged area, perhaps using a more refractory repair solder to avoid a repeat of the situation.