Exit failure of the refrigerant circulation system often causes a complete stop of the refrigeration chamber, and in most cases the problem lies precisely in a blockage or mechanical damage to a thin copper channel. The capillary tube acts as a choke, creating the necessary resistance for the transition of freon from a liquid to a gaseous state, so a violation of its tightness or throughput instantly disrupts the entire cooling cycle. Independent soldering of this unit requires not only specific equipment, but also a deep understanding of the thermodynamic processes occurring inside the circuit.
Before starting work, you must clearly understand that capillary tube has an internal diameter of only 0.6–0.8 mm, which makes it extremely sensitive to any contamination and deformation. An incorrectly executed seam can lead to re-clogging of the system or leakage of expensive refrigerant within a short time after starting the unit. In this material, we will analyze all the stages of replacing an element, from the selection of materials to final vacuumization, so that you can carry out the repair efficiently and safely.
The complexity of the procedure lies in the need to connect copper with steel, since the capillary is often soldered into the steel outlet tube of the evaporator or condenser. Using unsuitable solder or violating the temperature conditions leads to the formation of microcracks due to thermal expansion. That is why silver solder and the correct flux is not just a recommendation, but a prerequisite for the durability of the repair.
Necessary tools and materials for soldering
The quality of the work directly depends on the preparation of the workplace and the availability of specialized equipment. A standard household soldering iron is powerless here, since it requires local heating of copper to a temperature of 600–700°C without overheating neighboring areas. The main tool is a gas torch running on a propane-butane mixture or, ideally, oxygen with acetylene for a cleaner flame.
In addition to the fire source, you will need a pipe cutting kit, including a pipe cutter, a rimmer (rimmer) and a roller. Using a hacksaw for metal is strictly prohibited, as it creates small chips that will inevitably get inside the system and cause re-clogging. It is also critically important to have a vacuum pump and a pressure gauge station for the subsequent removal of moisture and air from the circuit. capillary tube. It is also critical to have a vacuum pump and a pressure gauge station to subsequently remove moisture and air from the circuit.
To connect dissimilar metals (copper-steel), you need a special solder with a silver content of at least 15-30%, for example, brand PSiAg 30 or its analogues. Brass solders are not suitable here due to the high melting point and the risk of burning through the thin walls of the tubes. As a flux, it is better to use special compounds for silver soldering, which do not require subsequent rinsing and do not form aggressive compounds.
⚠️ Attention: When working with open flames and flammable gases, be sure to provide powerful forced ventilation of the room. Flux combustion products and possible micro-leaks of residual freon can be toxic.
Diagnostics malfunctions and system preparation
Before starting dismantling, you need to make sure that the problem really lies in the capillary system. Typical signs of a blockage or break are a running compressor in the complete absence of cold in the chambers or, conversely, freezing of the condenser only in the initial part. If the refrigerator turns on and is immediately turned off by the thermal relay, this may indicate a water hammer or a complete lack of freon circulation.
Preparation begins by completely disconnecting the unit from the power supply and freeing access to the rear panel. Some models require partial or complete defrosting to prevent water from entering the compressor electrical components. After removing the casing, you must carefully bleed off the remaining refrigerant by cutting through the copper tube at a distance of 10-15 cm from the compressor.
The next step is to determine the exact soldering location. The capillary tube can be soldered directly into the filter drier or inserted into the evaporator body. If replacement is required, the new element must have an identical length and internal diameter, otherwise the balancing of the system will be disrupted. Length of the capillary tube is calculated by the manufacturer to the nearest millimeter, and its arbitrary change is unacceptable.
If you plan to simply clean the system, this often does not provide long-term results effect, since the cause of the blockage (moisture or oil breakdown products) remains inside. Therefore, a professional approach involves a complete replacement of the filter-drier and, if necessary, the capillary itself. Before soldering, all ends of the pipes must be perfectly smooth and free of oxides.
How to check the compressor before soldering?
To check the compressor, disconnect it from the system and apply voltage briefly. If it confidently sucks in air at the inlet and blows out with noticeable pressure at the outlet, the mechanical part is intact. Lack of suction or weak blowing indicates a breakdown of the valves or piston group.
Technology for soldering copper and steel connections
The soldering process requires skill in working with a flame in order to evenly heat the connection without melting the thin walls of the tubes. The burner flame must be adjusted so that the inner cone (core) is clearly defined, but does not touch the metal; heating occurs by the reducing part of the flame. First, the steel part of the joint is heated, since steel has lower thermal conductivity than copper, and only then the heat is transferred to the copper tube.
When the metal reaches the desired temperature (cherry-red color for copper), a solder rod is brought to the joint. Under the influence of temperature and capillary effect, the molten metal should itself flow into the gap between the pipes. It is critically important not to blow solder with a flame into the tubeas this will create an internal influx, which will reduce the cross-section and become a new center of clogging.
When connecting copper to steel, the method is often used copper sleeve inserts or use special adapters if direct soldering is not possible. During the heating process, it is necessary to constantly use flux, which cleans the surface of oxides and improves the fluidity of the solder. After forming the seam, the connection must cool naturally, without forced cooling with water or air, in order to avoid thermal stress.
☑️ Preparation for soldering
Replacing the filter-drier and installing a new capillary
The filter-drier is a disposable element that must be replaced whenever the refrigerator circuit is opened. Inside it is zeolite or silica gel, which absorbs moisture; If this element is not replaced, moisture will enter the capillary tube and freeze, forming an ice plug. The old filter is dismantled quickly in order to minimize contact of the insides of the system with atmospheric air.
Before installation, it is recommended to purge the new capillary with dry nitrogen to remove factory preservative grease and chips. When soldering a new element into a condenser or evaporator, the seating depth must be at least 15-20 mm to ensure a reliable connection. Often the capillary is wound in a spiral around the return line for heat exchange, and it is important not to damage it in the process.
After installing all the components, the circuit is assembled. All solder joints are visually checked for the presence of holes, sagging or signs of missing solder. Only after confidence in the tightness of the seams can you proceed to the next, most important stage - vacuuming and filling.
| Parameter | Value / Description | Criticality |
|---|---|---|
| Capillary diameter | 0.6 - 0.9 mm | High |
| Tube length | 1.5 - 4.5 meters | Critical |
| Temperature soldering | 650 - 750 °C | Average |
| Silver content | 15% - 45% | High |
Evacuation of the system and checking for tightness
Evacuation is the process of removing air and moisture vapor from the system, which is performed using vacuum pump. The remaining air creates an "air lock", increasing the condensation pressure and load on the compressor, and the moisture causes corrosion and freezing in the capillary. The process lasts at least 30-40 minutes, while the pressure gauge needle should go into deep vacuum (below -1 bar).
After creating a vacuum, the system is shut off and left for 15-20 minutes to check the tightness. If the pressure gauge needle starts to rise, there is a leak in the system that needs to be found and repaired by re-soldering. Ignoring this step will cause the refrigerator to stop cooling again after a few days or weeks.
Refrigerant charging is done only after successful evacuation. The amount of freon must strictly correspond to the label on the compressor or the model data sheet. Excess refrigerant will lead to freezing of the evaporator and possible water hammer, while too little will lead to compressor overheating and insufficient cooling.
⚠️ Attention: Refrigerant specifications and safety requirements may change. Always check the latest technical documentation from the manufacturer of your refrigerator model before refilling.
Frequent errors and safety measures during repair
One of the most common mistakes is overheating of the soldering area, which leads to the formation of an oxide film inside the tube and subsequent detachment of copper flakes. These scales inevitably fall into the narrow channel of the capillary, causing its blockage. Also, craftsmen often forget to replace the filter drier, considering it reusable, which is a fatal mistake for the durability of the repair.
Another problem is the use of inappropriate solder, for example, tin-lead, whose melting point is too low for the compressor to operate. Vibration and heat quickly destroy such a seam.
Safety when working with gases under pressure requires the use of protective glasses and gloves. A sudden release of refrigerant can cause frostbite to the skin and eyes. In addition, some modern refrigerants (for example, R600a) are explosive, so any work with open flames near them is strictly prohibited until the system is completely purged.
Is it possible to solder a capillary tube with a regular soldering iron?
No, a regular electric soldering iron is not capable of heating a copper tube to the temperature of 600-700°C required to melt solid silver solders. The use of soft solders (tin-lead) is unacceptable due to the low melting temperature threshold and vibration loads in the system.
What is the danger of an incorrect length of a new capillary tube?
A tube that is too long will create excess resistance, the compressor will work with overload, and the cooling capacity will drop. A tube that is too short will not provide the necessary throttling; liquid freon will enter the compressor, causing water hammer and rapid failure of the unit.
Is it necessary to flush the system after a capillary break?
If the break occurs due to blockage or moisture ingress, flush the system with nitrogen or a special solvent required. This will remove oil breakdown products and contaminants from the condenser and evaporator, which otherwise will quickly clog the new capillary and filter.