The internal structure of a modern refrigeration unit is a complex system of interconnected components, where each element performs a critical function. One of these key components, without which the generation of cold is impossible, is capillary tube, or, as masters often call it, a capillary. It is this thin copper element that is responsible for creating a pressure difference in the circuit, which allows the refrigerant to effectively evaporate and absorb heat from the chambers.
Understanding the operating principle of this part is necessary not only for professional repairmen, but also for those who want to better understand the physics of the processes occurring inside single-compressor and two-compressor systems. Unlike loud compressors or massive condensers, a capillary often goes undetected until a problem occurs. However, it is its condition that determines whether your refrigerator Indesit or Atlant freezes food or turns into a useless cabinet.
In this article we will look in detail at the design of the capillary tube, analyze the common reasons for its failure and discuss the nuances associated with blockages and replacement. You will learn why independent replacement of this element without specialized equipment is impossible and what risks are hidden by a violation of the tightness of the circuit.
The principle of operation and design of a capillary tube
Capillary tube is a long copper tube with a very small internal diameter, usually ranging from 0.6 to 0.9 millimeters. The length of this element can vary depending on the power of the compressor and the type of refrigerant used, reaching several meters, which is often realized by twisting the tube into a spiral for compact placement inside the unit. The main task of this component is to create hydraulic resistance a current of freon moving from the condenser to the evaporator.
The physics of the process is based on the pressure difference: after condensation into a liquid state, freon is under high pressure. Passing through the narrow opening of the capillary, the liquid is throttled and its pressure drops sharply. As a result of this difference the boiling point of the refrigerant is reduced to values significantly lower than the temperature inside the refrigeration chamber, which allows it to boil in the evaporator even at sub-zero temperatures, actively removing heat.
It is important to note that the capillary operates continuously while it is functioning compressor Unlike thermostatic valve (TRV), which can change its flow area depending on the load, the capillary tube has a constant diameter. This makes the system simpler and cheaper, but requires an accurate calculation of the length and diameter of the tube at the design stage of the refrigerator.
- 🔹 Creates the necessary pressure difference between the high-pressure and low-pressure parts of the circuit.
- 🔹 Meters the supply of liquid refrigerant into the evaporator in accordance with the performance of the compressor.
- 🔹 Prevents the backflow of liquid freon into the compressor during system shutdown.
- 🔹 Compensates for small fluctuations in the load on the cooling system.
The reliability of the design is due to the absence of moving mechanical parts. The copper from which the tube is made has excellent thermal conductivity and ductility, which allows the formation of complex loops. However, it is the small diameter that makes the element vulnerable to contamination and mechanical damage.
Symptoms of blockage and system malfunction
The most common problem faced by owners of refrigerators LG, Bosch and other brands is clogged capillary tube. Since the internal diameter is extremely small, even microscopic particles can completely block the refrigerant flow. This leads to the fact that the compressor continues to work, trying to pump freon, but the circulation in the system stops or becomes insufficient.
⚠️ Attention: Prolonged operation of the compressor with a clogged capillary leads to its overheating and eventual failure. If you hear the hum of the motor, but the cold does not appear, you must immediately turn off the power to the device.
You can determine the presence of a problem by a number of indirect signs. First of all, the temperature of the condenser (the grill at the back of the refrigerator) attracts attention. During a normal cycle, it should be hot evenly or with a gradient, but if clogged, heating can be local (only at the beginning) or absent altogether, since hot gas cannot pass beyond the blockage point.
Also a characteristic feature is the absence of the characteristic gurgling or hissing noise, which is usually heard when a working unit is operating. This is the sound of freon moving, and if it is not there, then the system is “locked”. At the same time, the compressor can work with increased load, consuming more electricity, but not doing any useful cooling work.
There are two main types of blockages, which are classified according to the nature of the originating substance:
- 🧊 Ice plug: Formed due to moisture entering the system. Water freezes at the narrowest point of the capillary, blocking the passage. Characterized by periodic thawing and re-freezing.
- 🗑️ Oil-mechanical blockage: Arises due to oxidation products of oil, varnish coating of compressor windings or metal shavings. Such a plug does not melt when heated and requires mechanical or chemical cleaning.
Diagnosis of the type of blockage is often made by exclusion or heating. If, when the capillary outlet from the filter drier is heated, the operation of the system is temporarily restored, then the problem lies in an ice plug or waxing of the oil.
Diagnostics: how to determine the type
Professional diagnostics begin with a visual inspection and listening. An experienced technician can determine the nature of the malfunction by the sound of the compressor running and the temperature of various sections of the circuit. To accurately determine the type, the heating method is used or, in more complex cases, opening the system.
If suspected ice plug, technicians often resort to heating the filter-drier and the beginning of the capillary tube. For this, construction hair dryers or special burners can be used. If, after heating, a characteristic sound of passing gas is heard and the refrigerator begins to freeze, the diagnosis is confirmed. However, this is a temporary measure, since the moisture in the system will not go anywhere and will soon freeze again.
Deeper intervention is required to identify it. mechanical blockage . A high-pressure nitrogen purge method is often used. If nitrogen does not pass through the capillary with the filter disconnected, then the tube is clogged with solid particles. In this case, simple cleaning may not help, and the element will need to be replaced.
It is also important to check the condition of the compressor oil. If it has a sour odor or has changed color to dark brown, this indicates overheating and decomposition, which is often accompanied by coking of the capillary tube with decomposition products.
Technology for replacing a capillary tube
Replacing a capillary tube is a complex repair process that requires specialized equipment and skills in working with refrigeration equipment. At home, it is almost impossible to perform this operation efficiently due to the need to evacuate the system and accurately dose the refrigerant.
The process begins with dismantling the old tube. It is necessary to carefully unsolder it from the filter drier and from the evaporator (or inlet pipe). Often the capillary is glued to the metal body of the evaporator for better heat transfer, so its removal requires care not to damage the thin-walled aluminum channels of the evaporator.
☑️ Steps for replacing the capillary tube
The new tube must have strictly defined geometric parameters. The length and inner diameter are selected in accordance with the compressor power and evaporator volume. Using the tube “by eye” will lead to incorrect operation of the system: either the compressor will be overloaded, or the evaporator will not be filled completely.
After installing the new element, the connections are soldered. It is critically important not to overheat the entry point of the capillary into the filter drier, since there is zeolite inside the filter, which, if heated strongly, can lose its properties or spill into the tube, creating a new blockage.
| Parameter | Impact on the system | Risk of error |
|---|---|---|
| Tube length | Determines the total resistance and amount of freon in the circuit | Too long - low suction pressure, overheating. |
| Diameter (internal) | Affects the throughput capacity and flow rate | Too wide - liquid freon will enter the compressor. |
| Depth of insertion into the filter | Provides filtration before throttling | Short depth - entry of unfiltered freon. |
The final stage is filling the system with refrigerant. The amount of freon must be strictly observed according to the nameplate on the compressor. A lack or excess of gas will disrupt the balancing provided by the new capillary.
Filter-drier: role in protecting the capillary
An integral pair for the capillary tube is filter drier. This cylindrical element is installed at the outlet of the condenser, immediately before the entrance to the capillary. Its main task is to remove moisture and mechanical impurities from the refrigerant, which directly protects the narrow channel of the tube from.
Inside the filter housing there is a mesh and an adsorbent (usually zeolite or activated aluminum oxide), which chemically binds water molecules. If the filter drier is oversaturated with moisture or clogged with slag, it ceases to perform its function, and moisture begins to migrate into the capillary, forming ice plugs.
If there is any depressurization of the circuit, be it the replacement of the compressor, evaporator or the capillary tube itself, the filter drier must be replaced. Reusing an old filter is unacceptable, since its adsorbing capacity has already been exhausted by contact with atmospheric air.
Why can’t you just blow out the filter?
Blowing the filter with compressed air or nitrogen does not restore its properties. Zeolite has a moisture saturation limit, and after contact with the atmosphere it requires regeneration at high temperatures in a vacuum, which is impossible at home.
There are universal filters that are suitable for most household refrigerators, however, for some models Liebherr or Siemens may require specific ones standard sizes with a threaded connection instead of a soldered connection.
Repair errors and safety precautions
Repairing a refrigeration circuit involves a number of risks, ignoring which can lead not only to equipment breakdown, but also to injury. Working with refrigerants requires compliance with strict safety rules, since many modern freons, when in contact with an open flame, decompose to form toxic substances.
One of the common mistakes is the use of oxy-acetylene burners without due care. Overheating of copper tubes can lead to the formation of oxides inside, which will subsequently cause a new capillary blockage. For soldering, it is recommended to use propane-butane mixtures or special solders with a low melting point.
⚠️ Attention: Never try to clean the capillary tube with wire or other mechanical means without removing it. You can damage the internal surface, which will lead to turbulent flow and noise, or pierce the tube in an inconspicuous place.
It is also dangerous to carry out work without vacuuming the system. Air and moisture remaining in the circuit will lead to increased condensation pressure, increased power consumption and rapid corrosion of the internal components of the compressor. A vacuum pump is a must-have tool for quality repairs.
Another mistake is ignoring the condition of the oil. If the oil in the compressor is not replaced when replacing the capillary (in case of serious contamination of the system), the new filter and tube will quickly fail. The acidity of the oil should be checked with indicator strips.
Questions and answers (FAQ)
Is it possible to replace the capillary tube with a similar one from another refrigerator?
Yes, but only if the internal diameter and length are the same. It is impossible to determine these parameters visually. It is necessary to use a tube of the same marking or carry out precise measurements with a micrometer, since a deviation of tenths of a millimeter will upset the balance of the system.
Why did the refrigerator begin to freeze worse after replacing the capillary?
Most likely, an error was made in the length of the tube or the amount of freon charged. It is also possible that air remained in the system or the filter drier was not replaced, which led to a partial repair immediately after repair.
How often should the capillary tube be changed?
The capillary tube does not have a limited service life and is replaced only in case of blockage or mechanical damage. With proper operation and the absence of moisture in the system, it can serve for decades together with the compressor.
Is it possible to clean the capillary without removing it?
In some cases, flushing the system with a special solvent (for example, R141b) under pressure, followed by purging with nitrogen, helps. However, if the blockage is mechanical (shavings, varnish), this method may not help, and the tube will have to be changed.
Is it dangerous to touch the capillary tube while the refrigerator is operating?
With a working system, the temperature of the capillary can be different: at the inlet it can be warm (after the condenser), and at the outlet it can be cold (after throttling). It is not dangerous to touch, but you can get a slight burn or frostbite depending on the area, so it is better not to touch the working elements unless necessary.