Capillary tube, or colloquially “capillary”, is one of the key elements of the refrigeration circuit, without which normal production of cold is impossible. This thin copper pipe connects the condenser and evaporator, creating the necessary throttling of the refrigerant. It is in this unit that a sharp drop in freon pressure occurs, which leads to its instant boiling and absorption of heat from the refrigerator chambers.
Many users do not even think about the existence of this part as long as the unit is working properly. However, if the capillary system fails, the refrigerator stops freezing or begins to work in increased mode, trying to gain temperature. Understanding the operating principle of this element will help you quickly diagnose the problem and avoid unnecessary expenses on calling a technician for minor repairs.
Modern models, be it Indesit, Atlant or LG, use a similar throttling principle. The length and diameter of the tube are calculated by engineers with mathematical accuracy for each specific compressor. Any deviation in the geometry or cleanliness of the internal channel can lead to a complete stop of the refrigeration cycle.
Principle of operation and physics of the process
The main function of the capillary is to create hydraulic resistance. The compressor forces the refrigerant at high pressure into the condenser, where the gas cools and turns into a liquid. In order for this liquid freon to boil again at a low temperature in the evaporator, it needs to suddenly release the pressure. Capillary tube acts as a narrow neck that allows a strictly dosed amount of liquid to pass through.
The throttling process occurs instantly. Passing through a narrow channel with a diameter of less than a millimeter, liquid freon loses pressure and part of it evaporates, forming a gas-liquid mixture. This mixture enters the evaporator, where it finally boils, removing heat from the products. Without this element, the pressure in the system would equalize, and the circulation of the refrigerant would stop.
It is important to understand that there are no moving parts in the system except the compressor. The movement of freon is ensured by the pressure difference created by the motor and maintained by the geometry of the tube. If the diameter is too large, the pressure will not drop and the evaporator will not cool. If it is too small, the compressor will work with overload, trying to push freon.
Design features and location
The capillary tube is a long copper coil. Depending on the power of the refrigerator, its length can vary from 2 to 6 meters, and the internal diameter ranges from 0.5 to 1 millimeter. This length is necessary to create sufficient resistance to the flow of refrigerant. The tube is often wound around the return line (suction tube) for heat exchange.
The location of the element depends on the design of the refrigerator. In most household models, it is hidden inside the thermal insulation layer or glued to the evaporator body. In dual-circuit systems, such as Stinol or Nord, two separate capillaries can be used for the freezer and refrigerator compartments, respectively. This allows you to regulate the temperature independently in each compartment.
The material is oxygen-free, high-purity copper. The use of other metals is prohibited due to the risk of a chemical reaction with the compressor oil or freon. The connection to the condenser and filter-drier is made by hard soldering, which guarantees tightness for decades.
Why is the tube so long?
A length of several meters is necessary to create laminar flow and stub resistance. If the tube were short, a microscopic diameter would be required, which would instantly become clogged with microparticles.
You can visually find the capillary by tracing the path from the filter-drier (usually a copper cylinder near the compressor) to the inlet of the evaporator. Often it has a characteristic bend or spiral before entering the foamed part of the body.
Symptoms of blockages and malfunctions
The most common problem is clogged capillary tube. Not only freon circulates in the system, but also a special oil that lubricates the compressor. Over time, if the seal is broken or poorly repaired, moisture, air or oxidation products may enter the circuit. They form ice or acid plugs that block the refrigerant flow.
The malfunction can be determined by indirect signs, without opening the unit. The compressor starts working continuously, without turning off, trying to compensate for the lack of cold. In this case, the motor itself may be hot, and the condenser grille at the back of the refrigerator may be cold or barely warm. This indicates that freon does not circulate through the system.
- 🌡️ Lack of cold: in the chambers the temperature is higher than normal, food begins to deteriorate, despite the operation of the motor.
- 🔊 Sound change: the operation of the compressor becomes more strained, gurgling sounds may appear or their complete absence after starting.
- ❄️ Local freezing: in some cases, only the beginning of the evaporator freezes, and the rest remains warm.
Another symptom is the formation of a “fur coat” or ice only at the entry point of the tube into the evaporator, while the rest of the area remains dry. This indicates that freon is passing through, but its amount is critically small due to partial.
Diagnostic and testing methods
Specialized equipment is required for accurate diagnostics. The initial check is carried out visually and auditorily. If the compressor is running, but the condenser is cold, this is a sure sign of a circulation problem. However, it is difficult to distinguish a clogged capillary from a freon leak or a compressor malfunction without instruments.
Masters use a pressure gauge station to measure the pressure in the system. When the compressor is switched off, the pressure must equalize. If, after starting, the pressure gauge needle on the suction side shows a deep vacuum, and on the discharge side shows high pressure, then the patency of the capillary tube is impaired. This is a classic sign hydraulic blockage.
There is also a method of purging with nitrogen. Having disconnected the tube from the evaporator, nitrogen is supplied under pressure through the filter. If gas flows freely with a whistle, the tube is clean. If the pressure does not drop or drops very slowly, it is obvious. Important: purging should be carried out only towards the freon outlet, so as not to drive debris deeper into the system.
| Symptom | Probable cause | Action |
|---|---|---|
| Compressor is hot, condenser is cold | Clogged capillary or filter | Replace the filter, purge with nitrogen |
| Ice only at the entrance to the evaporator | Partial or moisture | Evacuate, replace the desiccant |
| The compressor does not start | Electrical malfunction or wedge | Checking the starting relay |
| Noisy operation with gurgling | Extraneous noise or air | Checking the fastening, vacuuming |
Diagnostics must be carried out sequentially. First, electrical faults are excluded, then the tightness of the circuit is checked, and only then the permeability of the capillary system is analyzed.
Cleaning and repair technology
Repairing the capillary system is a complex process that requires skills and tools. Simple cleaning with a brush is impossible due to the small diameter and length of the tube. The main method of combating cm is flushing the circuit and replacing the filter drier. In some cases, it is necessary to replace the capillary tube itself with a new one of the same length and diameter.
The restoration process begins with dismantling the old filter and disconnecting the capillary from the evaporator. Then a special solvent or hot nitrogen is passed through the system under high pressure (up to 15-20 atmospheres). This allows you to dissolve oil deposits and push out solid particles. Filter drier change without fail, since its sorbent is already saturated with moisture and dirt.
☑️ Procedure for repair
If caused by moisture freezing (the so-called “ice”), the system must be thoroughly vacuumed. The vacuum pump removes water vapor, lowering the boiling point of the liquid, which allows moisture to evaporate even at room temperature. The process may take several hours.
⚠️ Attention: Using open fire to heat the tube for defrosting is strictly prohibited! This can lead to an explosion of freon vapor or deformation of the copper, which will completely disable the unit.
In difficult cases, when it is not possible to flush the tube, craftsmen resort to installing an additional capillary tube parallel to the main one or completely replacing the section. This requires accurate calculation so as not to upset the balancing of the system.
Replacing the capillary tube: nuances
Replacement of the element is required if cleaning is impossible or the tube is mechanically damaged (pinched, burst). It is critical to select a part with identical parameters. Diameter, length and even the roughness of the internal surface affect performance. Installing a tube from another refrigerator model may lead to incorrect operation.
When installing a new tube, cleanliness must be observed. Getting even microscopic dust inside the channel is unacceptable. The ends of the tube are sealed immediately after unpacking. The connection to the filter and evaporator is made with silver solder using flux. Copper should not be overheated, so as not to burn it and change the internal diameter.
After installing a new element, the system must be vacuumized for 30-60 minutes. This will remove air and remaining moisture. Then the refrigerant is charged strictly according to the weight indicated on the refrigerator nameplate. Overfilling or underfilling will lead to ineffective operation.
Independent replacement without soldering experience and the presence of a vacuum pump is practically impossible and risky. Errors lead to expensive repairs of the compressor, which can burn out due to operation without proper cooling or return of liquid freon.
Prevention and service life
The capillary tube is an element with an almost unlimited resource if there is no contamination in the system. Its service life is equal to the service life of the refrigerator itself. Problems arise solely due to external factors: poor-quality oil, moisture ingress during a previous repair, or a violation of the tightness of the circuit.
To prevent blockages, owners should avoid self-defrosting with sharp objects, which can damage the evaporator and introduce dirt. It is also not recommended to store the refrigerator in an unheated room at subzero temperatures, since condensation inside can cause corrosion.
- 🛡️ Tightness: monitor the condition of the seals to minimize moisture getting inside the chambers.
- 🔧 Quality repair: When filling with freon, require the use of a vacuum pump and a new filter.
- 🧹 Cleanliness: regular cleaning of the rear grille will improve heat transfer and reduce the load on the system.
If your refrigerator Bosch or Whirlpool stopped freezing, don’t rush to blame the compressor. Most often, the problem lies precisely in the disruption of the circulation of the refrigerant through the capillary system. Timely diagnostics will save significant money.
Is it possible to clean the capillary without disassembling the refrigerator?
Theoretically, you can try to blow the system through the process fitting if it is located at the beginning of the tube. However, without replacing the filter-drier and deep vacuuming, this will only give a temporary effect. Moisture and acid will remain in the system and will cause a relapse in a short time.
How much does it cost to replace a capillary tube?
The cost consists of the work of the master, the cost of materials (copper, solder, filter, freon) and the complexity of access. On average, repairs cost 30-50% of the cost of a new refrigerator. In some cases, it is cheaper to buy a new unit, especially if the model is old.
Why does the refrigerator freeze worse after repair?
Probably, a capillary tube of the wrong length or diameter was installed. It is also possible that there is air left in the system or moisture has not been completely removed. A repeated call to the technician is required to adjust the filling and check the vacuum.