Any breakdown of a household refrigerator, be it Indesit, Atlant or Liebherr, begins with alarm signals: the unit stops freezing, works non-stop, or makes unusual sounds. Often the root of the problem lies not in the compressor, which many mistakenly blame in the first place, but in the thinnest copper line hidden inside the thermal insulation of the housing. This part is called capillary tube, and it is the heart of the refrigerant circulation system.
It is this element that creates the necessary vacuum and pressure, allowing freon to change its state of aggregation and remove heat from the chambers. Without understanding how this unit works, it is impossible to carry out competent diagnostics or understand the reason for the sudden defrosting of food. In this article we will analyze the design of the system, the symptoms of its failure and ways to restore the functionality of the equipment.
The consideration of the issue will begin with the basic principles of thermodynamics used in everyday conditions, and will gradually move on to complex technical nuances, such as calculating the length of the line and soldering methods. You have to find out why even microscopic moisture inside the system can paralyze the operation of the entire unit. The length of the capillary tube for household refrigerators is strictly standardized and usually ranges from 2 to 4 meters, which is critical for creating correct throttling.
The principle of operation of the capillary choke
The capillary tube acts as a throttle, dividing the refrigeration machine circuit into two zones with different pressures: high and low. On one side of the line, immediately after the condenser, the refrigerant is under high pressure and has a temperature close to room temperature. Passing through the narrow opening of the tube, freon expands sharply, its pressure drops, and it turns into a cold vapor-liquid mixture.
This process, called throttling, is key to obtaining low temperatures in the evaporator. If there were no resistance, the refrigerant would circulate through the system without changing its phase state, and no cooling would occur at all. The diameter of the internal channel of the tube is extremely small, often less than a millimeter, which requires ideal cleanliness of the system.
It is important to understand that the tube has no moving parts and valves. All its work is based on physical resistance to the flow of gas and liquid. In modern models with the system No Frost the principle remains the same, but the requirements for the accuracy of refrigerant dosage become even higher due to the presence of additional heat exchangers.
⚠️ Attention: Replacing the compressor without replacing or purging the capillary tube and filter-drier in 90% of cases leads to repeated failure after a few months due to contamination of the system by oil combustion products.
The stability of the entire refrigeration unit directly depends on the throughput of this element. Any change in internal diameter or length instantly upsets the pressure balance. The compressor begins to work with overload or, conversely, cannot create a sufficient vacuum for freon to boil.
Design features and materials
Special high-purity copper is used for the manufacture of capillary lines. This material was not chosen by chance: copper has excellent thermal conductivity, ductility and resistance to the chemical effects of freons and refrigeration oils. The tube can be enclosed in a protective shell or pass directly through the body of the evaporator, sealed into aluminum channels.
Depending on the model of the refrigerator, the tube may have a different configuration. In some cases, it is simply wound in a spiral, in others it is built into the body wall for additional heating of the door perimeter, preventing the formation of condensation. This is the so-called heat exchanger, which increases the energy efficiency of the device.
A filter drier is always installed at the entrance to the capillary tube. This is a cylindrical element containing zeolite or silica gel, which retains moisture and mechanical particles. The presence of this filter is mandatory, since even a microscopic drop of water can freeze in a narrow channel and create an ice plug.
The tube is connected to other elements of the system by hard soldering. The quality of the seam is critical here, since the system is under pressure and vibration. The use of soft tin solders is unacceptable due to the low melting point and insufficient strength.
⚠️ Attention: When soldering copper joints, be sure to use filler gas (nitrogen) inside the tube to prevent the formation of an oxide film and sludge inside the line.
The length and internal diameter are selected by the manufacturer's engineers for each specific compressor model and refrigerant type (R134a, R600a). Unauthorized changes to these parameters during repairs are unacceptable, as they will lead to incorrect operation of the unit.
Symptoms of a malfunction of the capillary system
It is possible to determine that the problem lies in the capillary tube by a number of characteristic signs. Most often, users are faced with a situation where the refrigerator is humming, the compressor is running continuously, but there is no cold in the chambers. This indicates that the circulation of the refrigerant is impaired.
Another obvious symptom is the formation of a "coat" or ice build-up only in a certain location, usually near the evaporator inlet, while the rest of the system remains warm. This indicates that freon cannot pass beyond the clogged area and evaporates ahead of time.
It is also worth paying attention to the temperature of the condenser (grid at the back). If it is cold or only partially warm, and the filter drier is at ambient temperature (although it should be warm), this is a sure sign. In normal mode, the entire back wall should warm up evenly. clogging. In normal mode, the entire rear wall should be heated evenly.
Sometimes the malfunction manifests itself in cycles: the refrigerator freezes normally for a while, then stops, and after a long period of inactivity it starts working again. This is a characteristic sign of a “hydraulic” bottom when an ice plug in the tube either forms or thaws.
Types of blockages: oil, ice and mechanical
Understanding the nature of the blockage is critical for choosing a repair method. In total, there are three main types of blockage of the capillary system, and each requires its own approach to elimination.
Mechanical blockage occurs due to solid particles entering the system. This could be copper shavings from compressor wear, oil combustion products after overheating, or dust from poor installation. Such a blockage is often localized in the filter-drier itself or on the bends of the tube.
An ice plug is formed due to the presence of moisture in the circuit. Water enters the system when the seal is broken or low-quality refrigerant is used. Passing through the capillary, where the temperature drops sharply, the moisture freezes and blocks the cross-section. It is typical that when the compressor warms up, the plug may melt and the refrigerator temporarily begins to freeze.
Oil bottom is the most difficult case. It occurs when the oil loses its properties, thickens and waxes, blocking the flow of freon. This often happens in older refrigerators or when using incompatible types of oils. In this case, simple purging will not help; a complete flushing of the system is required.
How to distinguish an ice plug from a mechanical one?
An ice plug is often temporary: after turning off the refrigerator for several hours and turning it back on, it can begin to freeze until the moisture freezes again. Mechanical blockage is permanent and does not depend on operating cycles.
To accurately diagnose the type of blockage, technicians often use the method of alternately cutting off system elements and checking pressure, but at home this is extremely difficult to do without special tools.
Diagnostics and table of normal indicators
Professional diagnostics begins with a visual inspection and listening to the operation of the unit, but accurate data can only be obtained using a pressure gauge station. By connecting pressure gauges to the service fitting, the technician evaluates the suction and discharge pressure.
Normal pressure readings depend on the type of refrigerant and the ambient temperature. For R134a the pressure in the low pressure circuit must be negative (vacuum) or close to zero when the compressor is stopped, and during operation it must correspond to the boiling point. For R600a (isobutane) pressure is always positive, but below atmospheric pressure when stopped.
Below is a table of approximate temperature conditions for a working system at an ambient temperature of +25°C. Deviations from these values help to localize the problem area.
| System unit | Normal temperature | Symptom of malfunction |
|---|---|---|
| Compressor (housing) | 60-80°C | Overheating (>90°C) or cold |
| Discharge pipe | 70-90°C | Temperature below 50°C |
| Filter drier | Warm (40-50°C) | Cold or covered with frost |
| Capillary tube (inlet) | Sharp change (cold) | No temperature difference |
| Evaporator | Uniform cold (-18°C and below) | Cold only at the inlet |
If the filter drier is cold and the tube after it is warm, this is almost guaranteed to indicate a blockage. Normally, the filter should be warm, since compressed hot gas passes through it before throttling.
Diagnostics are also carried out using the “cut-off” method. The master carefully cuts through the capillary tube at the entrance to the evaporator. If gas noisily escapes from there, it means that there is passage to this place, and the blockage is located deeper in the evaporator or in the tube itself further along.
Methods for removing blockages and repairs
Repairing a capillary system is a complex technological process that requires a vacuum pump, a burner, pressure gauges and soldering skills. There are several ways to restore patency, the choice of which depends on the type of blockage.
The most common method is nitrogen pressing. The system is degermanized, the filter is cut off, and nitrogen is supplied to the tube under pressure of up to 15-20 atmospheres. This allows you to knock out mechanical impurities. However, this method is powerless against oil plugs.
To combat oil blockages and complex cases, flushing with special solvents, such as Solins R141b or RC-Flushis used. The liquid is charged into the system, circulates, dissolving deposits, and then is removed along with the dirt. After washing, thorough evacuation is required.
☑️ Algorithm for repairing the capillary system
In extreme cases, when it is impossible to flush the tube (for example, when the internal diameter is severely narrowed due to corrosion), it is replaced. This is a labor-intensive operation that requires “opening” the thermal insulation of the housing or installing a new tube over the old one (if the design allows).
⚠️ Attention: Never try to clean the capillary tube with wire or other mechanical means! You are guaranteed to damage the internal channel or pierce the tube, which will lead to the need to completely replace the evaporator.
After any intervention in the system, a vacuum procedure is required. It removes remaining moisture and air. The duration of evacuation should be at least 30-40 minutes for household refrigerators.
Prevention and operating rules
In order for the capillary tube to serve for a long time, it is necessary to follow the operating rules of the refrigerator. First of all, equipment should not be allowed to remain idle for long periods of time in an unheated room. Condensation formed inside can lead to corrosion and ice jams.
It is important to monitor the condition of the door seals. If they do not fit tightly, warm, moist air enters the chamber. The compressor wears out, trying to compensate for the heat flow, which leads to overheating of the oil and the formation of soot, which then clogs the capillary.
You should also avoid frequent power surges. Unstable operation of the compressor causes water hammer in the system, which can tear off metal particles from the valves and drive them towards the capillary tube.
Regular defrosting (for drip systems) and cleaning the condenser at the back of the refrigerator from dust also prolongs the life of the entire system. A clean heat exchanger ensures normal condensation pressure, reducing the load on the components.
Remember that modern technology is sensitive to the quality of service. An attempt to save on calling a technician and self-refilling without evacuation often ends in failure of the compressor, the cost of which makes up most of the price of a new refrigerator.
Frequently asked questions (FAQ)
Is it possible to replace the capillary tube with a longer or shorter one?
No, you can’t. The length and internal diameter of the tube are calculated by engineers to create a specific hydraulic resistance. Shortening the tube will reduce the resistance, the pressure in the evaporator will increase, the boiling point will increase, and the refrigerator will stop freezing. Extension will lead to overload of the compressor and possible freezing of the suction pipe.
Why did the capillary clog again after replacing the compressor?
Most likely, during the previous repair the system was not properly flushed. An old burnt out compressor releases a lot of acid and combustion products into the circuit. If you do not flush the system with a solvent and do not replace the filter drier, all the dirt will settle in the narrowest place - the capillary tube.
Is gurgling heard in the tube after the refrigerator stops - is this normal?
Yes, this is absolutely normal. After the compressor is switched off, the pressures in the high and low pressure circuits are equalized through the capillary tube. This process is accompanied by a characteristic sound of flowing refrigerant, which can last several minutes.
What is the danger of a clogged capillary tube for a compressor?
The clog creates high resistance. The compressor is forced to work at its limit to push the freon. This leads to overheating of the windings, destruction of insulation and eventual combustion of the motor. In addition, the lack of refrigerant circulation does not cool the compressor housing, which accelerates its breakdown.