Restoring the functionality of a refrigeration unit often requires precise manipulations with a copper pipeline, and one of the most common tasks is installing a service valve This procedure is necessary when the standard filling pipe is missing, damaged, or a complete replacement of the refrigerant in the system is required. Schrader valve allows you to create sealed access for connecting a pressure gauge station and a vacuum pump, ensuring control of the pressure in the circuit during maintenance.
The tapping process requires not only a specific tool, but also strict adherence to the technology for soldering copper pipes, since any mistake can lead to freon leakage or moisture entering the system. Tightness of connections is a critical parameter on which the service life of the compressor and cooling efficiency depend. In this guide, we will analyze in detail the stages of preparation, selection of insertion location and direct soldering.
It is worth considering that working with flammable gases and open fire near flammable materials requires increased caution. Before starting any actions, you must make sure that the work area is well ventilated and free of foreign objects. Proper preparation of tools and materials is the key to successful repairs, which will extend the life of your refrigerator for many years.
Preparation of tools and materials for soldering
The quality of the work directly depends on what exactly you are using. A standard household soldering iron is not suitable for soldering copper tubes of a refrigerator, since it is not capable of heating the metal to the required melting temperature of the solder. You will need oxygen-propane torch or a specialized torch with MAP gas, which provides the narrow and hot flame necessary for local heating without overheating adjacent sections of the tube.
The second important component is solder. For refrigeration systems, where pressure can reach high values and vibrations are constant, it is best to use silver-containing solder (with a silver content of 5% to 45%). It has high fluidity and strength, which is critical for vibration loads transmitted from an operating compressor. If there is no silver in the alloy, the connection may be less elastic and more susceptible to the formation of microcracks over time.
You will also need flux, but there is an important nuance: for copper-copper soldering, acid-free fluxes are often used, and for copper-steel (if you cut into the discharge line with a steel section) or copper-brass requirements may differ. Flux cleans the surface of oxides and improves the spreading of solder, but its residues can be aggressive, so after soldering they must be removed.
Don't forget about personal protective equipment. Working with open flames and hot metal requires fire-resistant gloves and safety glasses. When heated, copper emits a bright light that is harmful to the eyes, and flux splashes can cause burns.
- 🔥 Oxygen-propane torch with flame regulator for precise temperature control.
- 🪙 Silver-containing solder (for example, grades Castolin 105 or analogues) to create a strong seam.
- 🧪 Acid-free flux for soldering copper connections in refrigeration systems.
- 🛡️ Safety glasses and heat-resistant gloves for the safety of the master.
- 🧹 Metal brush and rags for cleaning surfaces before soldering.
Selecting the insertion location and diagnosing the system
Before picking up the torch, you need to determine exactly where the valve will be soldered. In modern refrigerators, the insertion is most often made into suction line (the tube going from the evaporator to the compressor), since it has the largest diameter and is made of copper, which simplifies soldering. Usually this is a section of copper tube in front of the compressor entrance, where there are no bends or damage.
However, if your goal is a complete refill or diagnostics, you may need to install a valve on the discharge line, although steel is often found there, requiring special soldering skills (use of bimetallic solders). It is important to choose a straight section of pipe with a length of at least 5-7 cm to provide convenient flame access and a place to install the service valve itself service valve.
Why can’t you solder next to plastic parts?
Plastic melts at much lower temperatures than melting solder. Even a short-term proximity to an open fire can deform the compressor housing or the insulation of the wires, which will lead to a short circuit or failure of the housing seal.
Before starting work, be sure to make sure that there is no excess pressure left in the system if it was previously damaged. If the refrigerator has simply stopped cooling and you plan to repair it, you need to carefully file the tube to bleed off the remaining gas. Refrigerant It should not come out abruptly, taking with it the compressor oil.
The place of future tapping must be thoroughly cleaned. Oxides and dirt will prevent the solder from spreading, creating a “sink” - a place for future leakage. Use fine-grained sandpaper or a special brush to clean the pipes until they shine. After cleaning, try not to touch the prepared surface with your hands, as skin fat also prevents high-quality soldering.
Schrader valve soldering technology
The soldering process itself requires skill and adherence to temperature conditions. First you need to warm up the connection. The torch flame should be directed at the pipe and not at the solder itself. Your task is to heat the copper to a temperature where it itself begins to melt the solder rods. If you only heat the solder, it may roll into a ball and not flow into the gap between the pipe and the valve fitting.
When the metal reaches the desired temperature (usually indicated by a change in color or by the reaction of the flux, if it is applied in advance), bring the solder to the joint. Silver-containing solder it should flow into the joint itself under the influence of capillary effect. There is no need to “smear” the pipe with solder, like paint; it is important that the molten metal fills the gap between the pipe wall and the base of the valve.
⚠️ Attention: Do not overheat the soldering area! If the copper becomes cherry red or begins to melt, you have overexposed the flame. Overheating changes the structure of the metal, making it brittle, and can burn the flux, which will lead to the formation of an oxide film inside the pipe.
After the solder has filled the joint, remove the torch and allow the joint to cool naturally. Do not blow on the tube or cool it with water, as sudden cooling can cause thermal shock and cracks in the seam or the metal itself. While the connection is hot, it is very vulnerable to mechanical stress, so do not touch the valve until it has completely cooled.
If you solder the valve into a cut pipe (using an adapter), make sure that the internal hole of the pipe is not blocked by solder. Excess solder flowing inside can create hydraulic resistance and disrupt the circulation of freon, which will lead to overload of the compressor. Experienced craftsmen often point the tube with the hole up or at an angle when soldering so that gravity helps control wicking.
☑️ Procedure for soldering a joint
Crimping the system and checking the tightness
After installing the valve and cooling the seam, you cannot immediately start filling the refrigerator. The first mandatory step is pressure test (nitrogen pressure testing). This is the process of creating excess pressure in the system to test all connections for leaks. To do this, a cylinder with dry nitrogen is connected to the installed valve through a reducer.
The pressure during pressure testing must exceed the operating pressure of the refrigerant in the system. For most household refrigerators with R134a or R600a freon, the pressure test is about 15-20 bar (atmospheres). After pumping up the pressure, the pressure gauge is closed and the system is left under pressure for at least 20-30 minutes, and ideally for 24 hours.
| Refrigerant type | Working pressure (bar) | Crimping pressure (bar) | Exposure time |
|---|---|---|---|
| R134a | 2.0 - 3.0 | 15 - 18 | min. 30 min |
| R600a (Isobutane) | 0.5 - 1.0 | 10 - 12 | min. 30 min |
| R404A | 8.0 - 10.0 | 25 - 30 | min. 1 hour |
| R22 (old models) | 4.0 - 5.0 | 20 - 25 | min. 1 hour |
If the pressure gauge needle has not moved a single division during the test, it means that the system is sealed and the valve soldering was successful. If the pressure drops, you need to look for a leak. Most often it is located precisely in the place of fresh soldering. You can locate the leak using a soap solution: apply thick foam to the seam and Watch for the appearance of bubbles.
Using ordinary air or moist gas will result in moisture remaining inside the system. When the refrigerator is running, moisture will freeze in the capillary tube, forming an ice plug, or react with the oil and refrigerant, forming acid that will corrode the compressor from the inside.
Vacuuming and preparation for refueling
After successful crimping, the vacuuming stage begins. The nitrogen remaining in the system must be vented and then connected to the service valve vacuum pump. The purpose of this stage is to remove not only air from the circuit, but also moisture vapor that inevitably got there during repairs. Water in the refrigerator system is the main enemy, capable of destroying equipment in a matter of weeks.
The process of pumping out air takes from 15 to 30 minutes, depending on the power of the pump and the volume of the system. The residual pressure should reach a value of about 500 microns (or the maximum possible for your equipment). After reaching a vacuum, the valves of the pressure gauge station are closed, the pump is turned off, and the system is left under vacuum for another 10-15 minutes for control.
If the pressure gauge needle (or vacuum gauge readings) remains stable and does not creep up, this confirms tightness and the absence of moisture that could evaporate. If the pressure increases, it means that there is a leak in the system or moisture continues to come out of hard-to-reach places (for example, from the oil in the compressor), and the evacuation process must be repeated, perhaps with the compressor warmed up.
⚠️ Attention: Never turn on the compressor if a vacuum has been created in the system, without first releasing the gases! Working “dry” or in a vacuum can lead to breakdown of the insulation of the electric motor windings or collapse of the compressor housing under atmospheric pressure if there are defects.
Only after successfully completing the evacuation stage can you begin to fill the refrigerator with refrigerant. The Schrader valve that you soldered now serves as the main port for introducing freon in strict accordance with the weight indicated on the factory sticker of the refrigerator.
Common mistakes and advice from professionals
Even experienced professionals make mistakes, not to mention beginners. One of the most common problems is the formation of an oxide film inside the pipe during soldering. To avoid this, professionals recommend blowing the pipe inert gas (nitrogen) during the soldering process. The nitrogen flow displaces oxygen from the pipe, preventing oxidation of copper from the inside.
Another common mistake is the wrong choice of location for the valve. If the valve is cut too close to the compressor housing, vibrations can quickly loosen the solder joint. Also, on hot discharge lines, the plastic of the valve body can melt if it is not designed for high temperatures. Always use metal valves for high temperature lines.
- 🌡️ Control the temperature: copper should be red, but not melting.
- 💧 Use only dry nitrogen for pressure testing to avoid corrosion.
- ⏱️ Do not rush to cool: natural cooling guarantees the strength of the seam.
- 🧼 Carefully remove flux residues after soldering to avoid corrosion.
It is also worth mentioning the quality of the valve itself. Cheap Chinese analogues may have defects in the spool mechanism or threads. Before soldering, it is recommended to check the valve visually and, if possible, blow it out. Brass bodies valves are soldered easier than steel ones, but require care, since brass is an alloy of copper and zinc, and with severe overheating, zinc can burn out, worsening the properties of the metal.
Is it possible to use a car nipple instead of a Schrader valve?
Theoretically it is possible, but this is bad practice. Car nipples are not designed to withstand refrigerator vibrations and may leak freon. Specialized service valves have a design that eliminates leaks when connecting hoses multiple times.
Is it necessary to change the filter drier when inserting the valve?
Yes, any time the refrigerator circuit is opened (and inserting the valve is an opening), the filter drier must be replaced. The old filter is already saturated with moisture from the air during soldering and will not be able to properly dry the system, which will lead to rapid failure of the equipment.
Which solder is better: with or without flux inside?
For refrigeration equipment, it is preferable to use rods without flux inside, applying flux separately. Rods with flux inside (self-fluxing) often contain more aggressive components that are more difficult to completely remove from a narrow tube, which creates a risk of corrosion in the future.
What to do if the solder does not stick to the copper?
Most likely, the surface is not sufficiently cleaned or underheated. The copper must be perfectly clean and heated to a temperature above the melting point of the solder. Also check the expiration date and quality of the flux - old or dried flux does not work.
Is it dangerous to solder the valve on a running refrigerator?
It is absolutely forbidden to solder the valve if there is pressure or refrigerant residue in the system. This may result in an explosion or fire (especially with R600a freon). All work is carried out only after complete bleeding of gas and evacuation or on new, empty units.
Is it possible to replace the Schrader valve without turning off the compressor?
No, for a quality installation of the valve, the compressor must be disconnected from the network, and the system must be prepared (evacuated or bleed). Installation under pressure is impossible and life-threatening.