The internal structure of the refrigeration unit is a closed circuit through which refrigerant circulates, providing cooling to the chambers. The central element of this system, responsible for creating the necessary pressure drop, is the capillary tube. It is this thin copper element that separates the high and low pressure zones, allowing freon to effectively release heat to the environment.
Many users are faced with a situation where the refrigerator stops freezing, and the technician diagnoses a blockage in the system. Understanding what is a capillary in a refrigerator and how it affects the operation of the compressor will help you better understand the causes of malfunctions. Without this microelement, the circulation of the refrigerant would be impossible, and the refrigerator would turn into a useless box.
In this article we will analyze in detail the principle of operation of the capillary tube, the reasons for its failure and the nuances of replacement. You will learn why the diameter of this element is selected with high precision and what consequences may arise if the wrong analogues are selected for repair.
The principle of operation of a capillary tube in a refrigeration circuit
A capillary tube is a long, very thin copper pipeline that serves as a throttling device in a refrigeration machine. Its main task is to create resistance to the flow of the refrigerant, which leads to a sharp drop in pressure and temperature of the liquid before it enters the evaporator. Throttling is a key physical process, without which the operation of any household refrigerator is impossible.
The process can be described as follows: the compressor compresses freon gas, increasing its pressure and temperature. The hot gas then enters the condenser, where it cools and turns into liquid. It is in the liquid state that the refrigerant approaches the entrance to the capillary. Passing through the narrow opening of the tube, the pressure drops sharply, and part of the liquid instantly evaporates, cooling to very low temperatures. Boiling point Freon at atmospheric pressure is about -30°C, which ensures cooling of the products.
⚠️ Attention: The capillary tube is designed to work only with liquid freon. If gas or moisture gets into the system, the throttling efficiency will drop, which can lead to freezing or, conversely, insufficient cooling.
The length and internal diameter of the tube are selected by engineers individually for each refrigerator model. Changing these parameters even by millimeters can upset the balance of the entire system. Hydraulic resistance must be strictly defined so that the compressor can push the refrigerant through a narrow opening, but still provide the required evaporator performance.
Design features and manufacturing materials
The main material for the manufacture of capillaries is oxygen-free, high-purity copper. This metal was not chosen by chance: it has excellent thermal conductivity, ductility and resistance to corrosion within the system. The standard internal diameter of the tube varies from 0.6 to 2.0 mm, and the length can reach several meters, although in household refrigerators it is often twisted into a compact spiral.
In modern models of refrigerators Indesit, Atlant or Beko the capillary tube is often soldered to the filter-drier on one side and to the evaporator or compressor inlet on the other. An important design feature is the tight contact of the tube with the return line (suction pipe). This heat exchange device allows you to:
- 🧊 Cool liquid freon before entering the capillary, increasing cooling capacity.
- ❄️ Heat gaseous freon before entering the compressor, preventing water hammer.
- 💧 Eliminate entry of the liquid fraction into the compressor cylinder, which prolongs the service life of the motor.
There are also models with two capillaries, where one circuit serves the freezer compartment, and the second - the refrigeration compartment. This scheme allows you to independently regulate the temperature in different zones, however, it is more difficult to maintain and the maintainability of such systems is lower.
When replacing a part, it is extremely important to use a tube with identical geometric parameters. Using larger diameter copper tubing will result in insufficient resistance and the compressor will work overload trying to create a vacuum. A capillary that is too narrow will create excess pressure at the outlet of the compressor, which also leads to an emergency stop.
Why copper and not aluminum?
Aluminum is cheaper, but it is less ductile and less amenable to soldering at home. Copper allows you to create reliable connections using the silver soldering method that can withstand high pressure and vibration without the risk of depressurization.
Main causes of clogging and failure
The most common problem faced by refrigerator owners is clogging of the capillary tube. Since the hole diameter is minimal, even microscopic particles can block the refrigerant flow. Blockages are divided into two main types: mechanical and ice (acid).
Mechanical blockage occurs due to foreign particles entering the system. This could be copper scale remaining after a poor-quality previous repair, compressor wear products (metal shavings) or flux residues. An ice plug forms when there is moisture in the system. Water, freezing in the narrowest part of the capillary, completely blocks the passage.
Acid blockage is a more complex chemical process. When the compressor oil overheats or gets exposed to moisture, acid can form and react with the copper, creating hard deposits. These deposits gradually narrow the flow area until circulation stops completely. Symptoms of a blockage usually appear as follows:
- 🔇 The compressor works continuously, but there is no cold.
- 🌡️ The condenser (grid at the back) remains only partially cold or warm.
- ❄️ The evaporator inside the chamber does not freeze evenly or is covered with frost only at the entrance.
Diagnostics are carried out by palpating the tubes and measuring pressure. If the tube after the filter drier is hot and after the capillary is cold (or vice versa, depending on the location of the blockage), this is a sure sign of a problem. The technician can also cut off the capillary and try to blow it with nitrogen.
⚠️ Attention: An attempt to blow the system with your mouth or a compressor without drying is strictly prohibited. Introducing moisture into the system will lead to the instant formation of an ice plug and failure of the compressor in the shortest possible time.
Diagnostics of capillary system malfunctions
Before proceeding with replacing the capillary, you must be sure of the diagnosis. Symptoms may be similar to a freon leak or a compressor malfunction. Primary diagnostics includes a visual inspection and tactile check of the temperature conditions of various sections of the circuit.
With a working system, after the filter-drier, the tube should be warm, and after passing through the capillary and entering the evaporator, it should be sharply cold. If the capillary is clogged, the area before the clog will be hot (due to high pressure), and after it will be at room temperature. If a break or complete blockage occurs, the compressor can run “idle”, creating a characteristic sound, but without pumping gas.
For accurate diagnosis, technicians use a pressure gauge manifold. By connecting it to the process pipe, you can see the pressure in the system. If the capillary is clogged, the pressure on the suction side will tend to a deep vacuum, and on the discharge side it will significantly exceed the norm.
☑️ Signs of a clogged capillary
It is also important to check the filter drier. It is often the primary barrier to debris, and replacing it can solve the problem without interfering with the capillary itself. However, if the blockage has formed inside the turns of the tube, replacing the filter will not help - a complete overhaul of the system will be required.
Technology for replacing a capillary tube
Replacing a capillary tube is a complex technical process that requires special equipment and skills. It is not a simple DIY repair, as it involves working with an open circuit, evacuation and charging with refrigerant. The process begins with dismantling the old tube and selecting an analogue with identical parameters.
The master unsolders the old capillary from the filter and evaporator. Then the system is cleaned of old oil and possible debris. This is done by purging with dry nitrogen at high pressure. Only after complete cleaning is a new filter-drier installed and a new tube soldered in.
The critically important step is vacuum. The system must be free of air and moisture. For this purpose, a two-stage vacuum pump is used, which pumps out gases to a pressure close to absolute vacuum. The evacuation time depends on the power of the pump and the volume of the system, but is usually at least 30-40 minutes.
After evacuation, the refrigerator is charged with freon. The amount of refrigerant is strictly regulated by the manufacturer and is indicated on the label (usually in grams). Refilling is done on scales for dosing accuracy. Excess or lack of freon will lead to incorrect operation of the refrigerator.
| Repair stage | Description of action | Necessary tool |
| :--- | :--- | :--- |
| Dismantling | Cutting off the old tube, removing the filter | Pipe cutter, burner |
| Cleaning | Purging the circuit with nitrogen | Nitrogen cylinder, reducer |
| Installation | Soldering a new capillary and filter | Burner, solder, flux |
| Vacuuming | Removing air and moisture | Vacuum pump, manifold |
| Refueling | Dosed introduction of freon | Scales, cylinder with freon |
Prevention and operating rules
To extend the life of the capillary system and the entire refrigerator, it is important to follow the operating instructions. The main enemy of the system is moisture and dirt. Never leave the refrigerator open for a long time when the compressor is not running, as this contributes to the saturation of the oil and tubes with atmospheric moisture.
Frequent cycles of turning on and off the device should also be avoided. Sudden pressure surges can accelerate compressor wear and contribute to the formation of deposits in tight spots. Regular defrosting (for No Frost models this is less important, but for drip systems it is important) helps maintain the efficiency of heat transfer.
If you notice that the refrigerator has begun to work worse, do not delay calling a technician. Operating a system with a clogged capillary will cause the compressor to overheat and may result in costly replacement. Timely prevention and replacement of the filter-drier during any intervention in the system is the key to long service life of the equipment.
⚠️ Attention: All work related to opening the refrigeration circuit must be carried out by a qualified specialist using personal protective equipment. Freon, upon contact with an open flame, decomposes to form phosgene, a poisonous gas.
Following these simple recommendations will allow your refrigerator to operate reliably for many years. Remember that the capillary is the “heart” of the hydraulic cooling system, and its health determines the efficiency of the entire device.
Is it possible to restore an old capillary?
In industrial conditions, there is a method of washing with a special solvent under pressure, but in domestic conditions this is impractical. It is cheaper and more reliable to replace the tube and filter with new ones.
Frequently asked questions (FAQ)
Is it possible to replace a copper capillary with an aluminum one?
Theoretically it is possible, but it is highly not recommended. Aluminum is more difficult to solder, less ductile, and more susceptible to corrosion under certain conditions. Copper is a standard for refrigeration equipment, and replacing it with another metal can disrupt heat transfer and the tightness of the system.
How much does it cost to replace a capillary tube?
The cost consists of the price of materials (copper tube, filter, freon, solder) and the work of the craftsman. On average, repairs cost 30-40% of the cost of a new refrigerator, but the exact price can only be found out after diagnosing a specific model.
Why does the refrigerator freeze worse after replacing the capillary?
There may be several reasons: the diameter or length of the tube is incorrectly selected, insufficient evacuation of the system (moisture remains), incorrect dose of freon filling or the presence of air in contour. Repeated diagnostics are required.
How to understand that the capillary is clogged and not a freon leak?
If there is a leak, the pressure in the system will be atmospheric or close to it, and the compressor will operate with low current. When the capillary is clogged, the compressor creates a vacuum at the inlet and high pressure at the outlet, consuming increased current.
Does it need to be replaced when replacing the capillary?
Not necessary if the compressor is working properly. However, if the blockage was caused by wear products of the motor (black oil, chips), then replacing the capillary without replacing the compressor will lead to re-clogging in the shortest possible time.