In the design of modern refrigeration equipment, each element performs a critical function, providing stable cold in the chambers. One of the key components of the system is capillary tube, which often becomes the cause of malfunctions if its tightness or capacity is violated. Understanding the principle of operation of this part allows owners of household appliances to independently diagnose a number of typical problems, such as insufficient cooling or no cold at all.
This thin copper element serves as a kind of throttle separating the high and low pressure zones in the refrigerant circuit. Without it, proper circulation of freon and, as a result, effective heat exchange is impossible. In this article we will analyze in detail the structure of this system, the symptoms of its failure and the algorithm of actions if repairs are necessary.
Many users mistakenly believe that the tube performs only a transport function, but its role is much more complex. It is here that a sharp drop in refrigerant pressure occurs, which triggers the process of evaporation and heat removal from the internal volume of the chamber. Modern models of refrigerators This element may have different lengths and diameters, which directly affects the performance of the compressor.
Principle of operation and design of the throttle element
The capillary tube is a long, very thin copper pipe that connects the condenser (where the refrigerant is in a liquid state under high pressure) and the evaporator. Passing through this narrow channel, freon experiences strong hydraulic resistance. As a result of this process the pressure decreases sharplyand the boiling point of the substance drops, which allows it to actively boil in the evaporator even at low temperatures.
The diameter of the internal section of the tube usually varies from 0.6 to 2 millimeters, and the length can reach several meters, being wound in spiral for compactness. This geometry was not chosen by the manufacturer by chance: it ensures a precise balance between the amount of liquid refrigerant supplied and the compressor’s ability to pump out vapors. Violation of this balance leads to incorrect operation of the entire system.
It is important to note that, unlike mechanical thermostatic valves, the capillary tube has no moving parts and works solely due to the laws of physics. This makes it reliable, but also vulnerable to contamination. If moisture or oil breakdown products appear in the system, they can crystallize and block the narrow cross-section, causing the so-called ice plug effect ice cork effect.
⚠️ Attention: When inspecting the tube yourself, do not bend it at an acute angle under any circumstances. Deformation of the internal channel will irreversibly violate the design pressure, and the refrigerator will stop freezing, even if the compressor is working.
There are different types of tubes used in household refrigerators different generations. Some models are equipped with heat exchangers, where the capillary tube is soldered to the suction line to increase efficiency. This allows you to additionally cool the liquid freon before entering the evaporator and heat the vapor before the compressor, preventing the liquid fraction from entering the cylinder of the unit.
Why copper?
Copper is used for the manufacture of capillary tubes due to its high thermal conductivity, ductility and corrosion resistance. Aluminum or steel can also be used, but copper provides the best balance between installation flexibility and durability in the face of compressor vibration.
Main functions in the refrigeration cycle
The main task of this element is to create a pressure drop. At the entrance to the tube, the pressure can be 9-12 atmospheres (condensation zone), and at the outlet it can drop to 0.1 atmospheres (evaporation zone). Without this difference, freon would not be able to effectively transition from a liquid to a gaseous state, removing heat from the products.
The second important function is dosing the refrigerant supply. The tube passes exactly as much liquid as can be evaporated by this particular evaporator at the current load. If the supply were excessive, liquid freon could enter the compressor, causing water hammer - mechanical destruction of the valves. If the flow is insufficient, the evaporator will not fill completely and the cooling capacity will drop.
The third function is to maintain a constant flow. Unlike intermittent systems, the capillary tube provides continuous circulation while the motor-compressor is running. This simplifies the design of the refrigerator and reduces the number of points of potential failure.
- 🧊 Provides a sharp decrease in refrigerant pressure before entering the evaporator.
- ⚖️ Meters the amount of liquid freon, preventing compressor overload.
- 🔄 Maintains continuous circulation cycle of the working substance in a closed loop.
- 🛡️ Protects the system from water hammer, ensuring complete evaporation of the liquid.
It is worth considering that the performance of the tube depends on the viscosity of the refrigerant, which, in turn, depends on the temperature. Therefore refrigeration systems are designed taking into account operation in a certain temperature range. Replacing the original tube with an analogue with other geometric parameters is unacceptable without recalculating the entire system.
Symptoms of clogging and malfunctions
You can determine that the capillary tube of the refrigerator has failed by a number of characteristic signs. Most often, users are faced with a situation where the compressor runs continuously, hums, but the cold does not appear in the chambers or there is not enough of it. This is a classic symptom of poor circulation.
Another sign is uneven cooling of the evaporator. If, when the engine is running, one part of the radiator is hot and the other is cold, or the tube is warm only at the inlet and cools down sharply at the site of the blockage, this indicates a problem. In normal conditions, the temperature should decrease gradually along the entire length.
It is also worth paying attention to the behavior of the thermostat. If it clicks, starting and stopping the motor too often, or, conversely, does not turn it off for hours, perhaps the pressure in the system does not reach the required values due to an obstruction in the channel.
In some cases, the blockage may be temporary, the so-called “floating”. For example, when moisture accumulates in the system, an ice plug can form, which periodically melts and freezes again. This leads to a cyclical appearance and disappearance of cold, which often confuses diagnostics.
Diagnostics: how to check patency
To accurately diagnose the condition of the capillary tube, specialized tools and skills in working with refrigeration equipment are required. The initial inspection is carried out visually: the technician looks for traces of oil, which may indicate microcracks or kinks. However, internal blockages cannot be detected in this way.
The main test method is purging with nitrogen under pressure. Having disconnected the tube from the filter drier and evaporator, connect a cylinder with dry nitrogen to it. If the air flows freely with a characteristic whistle, then the channel is clean. If the pressure does not drop or drops very slowly, there is a mechanical blockage.
The vacuum test method is also used. A vacuum pump is connected to the system, and a pressure gauge monitors how deeply and quickly the pressure drops. If the vacuum does not hold or is not achieved, this indicates an obstruction in the line.
| Diagnostic method | Required equipment | Normal indicator | Symptom of malfunction |
|---|---|---|---|
| Visual inspection | Flashlight, magnifying glass | Smooth surface, no oil | Blisters, traces of oil, kinks |
| Purge with nitrogen | Nitrogen cylinder, gearbox | Free passage of air | Pressure does not drop, silence |
| Evacuation | Vacuum pump, pressure gauge | Quick vacuum set | Arrow stays still |
| Current test | Current clamps | Current within the limits of the passport | Underestimated current (no load) |
Residual pressure can distort the test results and create a dangerous situation when unsoldering parts.
⚠️ Attention: Never use ordinary air to purge the system compressor Its air contains moisture and oil, which will instantly create a new, even more complex blockage in the capillary tube.
Technology for replacing the capillary tube
Replacing a capillary tube is a complex repair that requires adherence to strict technology. The process begins with dismantling the old part. To do this, you need to carefully unsolder the connections between the tube and the filter-drier and evaporator using an oxygen-propane torch.
After dismantling, a new tube is selected. It is critical to maintain the length and internal diameter of the original. Sometimes craftsmen use the “pricking” method, inserting a new tube into an old sleeve on the evaporator, so as not to overcook the entire radiator, but this is not permissible in all cases.
The next stage is soldering. Before installing a new part, the filter drier must be replaced, since the old one is already saturated with moisture and will not be able to work effectively. Soldering is done with silver solder or a special high-temperature solder for copper, which ensures the tightness of the seam.
☑️ Algorithm for replacing the tube
After installation, the system must be vacuumized for a long time (usually at least 30-40 minutes) to remove moisture and air. Only after creating a deep vacuum is refilling with the exact amount of refrigerant indicated on the refrigerator nameplate.
Common mistakes during self-repair
Attempts to repair a refrigerator without proper experience often lead to aggravation of the situation. One of the most common mistakes is neglecting to replace the filter drier. An old filter will not be able to remove moisture that entered the system during repairs, which in a short time will lead to the re-formation of an ice plug.
Another mistake is using the tube “by eye”. Owners often take any copper tube of suitable diameter, without taking into account the length. Shortening the tube will lead to a drop in condensation pressure and overload the compressor, and lengthening it will lead to underheating of the evaporator and poor cooling.
The third mistake is poor soldering. Overheating of copper leads to the formation of oxides inside the tube, which immediately become a new blockage. Underheating leads to leakage of the seam and leakage of freon in the very first hours of operation.
- ❌ Lack of evacuation of the system before refueling.
- ❌ Using a tube of the wrong length or diameter.
- ❌ Reusing an old filter-drier.
- ❌ Overheating of the soldering area, causing oxidation of the internal walls.
It is also worth mentioning the error associated with the type of refrigerant. Modern eco-friendly refrigerants (for example, R600a) require special care when soldering due to their flammability. An attempt to fill such a refrigerator with freon R134a or R12 “by eye” without a scale will lead to incorrect operation or an explosive situation.
Is it possible to clean the tube without replacing it?
Theoretically, in case of mechanical blockage (dust, dirt) high-pressure nitrogen purging is possible. However, if clogged with oil breakdown products (acid clog) or moisture, cleaning is impossible - a complete flushing of the system, replacement of the compressor oil, filter and capillary tube are required.
Prevention and service life
The capillary tube does not have a specific service life in years, since it is a static element. It serves as long as the system remains clean and tight. The main enemies of the part are moisture and oxidation products formed during improper operation or poor-quality previous repairs.
To prevent malfunctions, it is recommended not to store the refrigerator in an unheated room at subzero temperatures if it is not intended for this. Condensation inside the system can freeze and damage thin walls or create a blockage.
It is also important to monitor the condition of the door seals. If a lot of warm, humid air enters the chamber, the load on the system increases, which can indirectly affect the operation of the throttle element and accelerate the wear of the compressor.
⚠️ Attention: If your refrigerator has been repaired, always request a certificate of work performed indicating the type of refrigerant charged and parts replaced. This will help the technician at the next call to quickly understand the cause of a possible breakdown.
Timely defrosting (for No Frost systems - cleaning the drainage) also helps maintain optimal operating conditions. Although the capillary tube is located inside a sealed circuit, the general condition of the heat exchangers affects the pressure and temperature in the system, which affects the life of all components.
FAQ: Frequently Asked Questions
Is it possible to replace the capillary tube yourself without special equipment?
No, it is not possible. Replacement requires sealing the system, using nitrogen to purge, a vacuum pump to remove moisture, and a scale to accurately charge the refrigerant. Without this, the refrigerator will not work.
What is the diameter of a standard capillary tube?
There is no standard diameter. Depending on the compressor power and the type of refrigerant, tubes with a diameter of 0.6 mm to 2.0 mm are used. Using the wrong diameter will disrupt the operation of the refrigerator.
Why does the refrigerator freeze but does not turn off after replacing the tube?
Most likely, the length of the new tube is chosen incorrectly (it is too short) or there is an excess amount of refrigerant left in the system. Also, the reason may be the incorrect operation of the thermostat, which does not sense the required temperature.
What is the danger of a clogged capillary tube for a compressor?
When completely clogged, the compressor operates in vacuum mode at the suction, which can lead to overheating of the windings and their interturn short circuit. In addition, the lack of circulation of freon means the lack of cooling of the motor itself, which accelerates its wear.
How long does it take to professionally replace a capillary tube?
A qualified technician performs this work within 1.5–2 hours, including time for preparation, soldering, vacuuming (at least 30-40 minutes) and refilling refrigerant. Rushing in this process is unacceptable.