Visual identification of the capillary tube in a household refrigerator often causes difficulties for those who look into the technical compartment of the unit for the first time. This component is a long, thin copper pipe that visually appears to be part of a complex maze of cooling system. Unlike thick lines through which the refrigerant moves under high pressure, capillary tube has a minimal internal diameter, which determines its name and functional purpose.
When examining the back of the refrigerator, where the compressor is located, you will notice that the tubes are intertwined, and some areas are wound spiral. It is in this area, usually near the entrance to the evaporator or inside the thermal insulation, that the required element is hidden. Understanding what this unit looks like is necessary for the initial diagnosis of malfunctions, such as lack of cold or the formation of an ice coat in unintended places.
It is important to note that the appearance of the tube may vary depending on the model of the refrigerator, be it classic Atlant, modern Bosch or Indesit. However, the design features remain unchanged: it is always copper, a characteristic bend and a specific soldering location. Next, we will look in detail where exactly to look for this element and how to distinguish it from other parts of the circuit.
Design features and appearance
The capillary tube is, in fact, a choke of the refrigeration system. Visually, it is a copper conductor with a diameter of 0.6 to 3 millimeters, although in household refrigerators a size of about 0.8–1.0 mm is most often used. The length of this element can reach several meters, so in the factory it is rolled into a tight spiral or laid in a zigzag pattern in order to be compactly placed inside the case or behind the back wall.
The manufacturing material is exclusively copper, since this metal has high ductility and excellent thermal conductivity. On the cut or at the joints you will see a characteristic reddish-golden hue. The surface of the tube is usually smooth, but there may be thickenings at the soldering points - these are the junctions with the condenser and evaporator. Sometimes the tube is covered with a layer of thermal insulation or soldered to the return tube from the compressor for heat exchange.
- 🔍 Diameter: The internal cross-section is strictly calibrated, any change in size makes the tube unsuitable for use.
- 🔍 Length: Varies from 1.5 to 4.5 meters depending on the power compressor and type of refrigerant.
- 🔍 Shape: Often has a spiral winding at the evaporator inlet for uniform flow distribution.
⚠️ Attention: Copper is a soft metal. When trying to straighten a twisted capillary tube for inspection, damage its integrity, which will lead to instant depressurization of the circuit.
On modern models of refrigerators, such as Liebherr or Samsung, the capillary tube can be completely hidden in polyurethane foam insulation of the body. In such cases, it is possible to visually check its condition only in the area of entry into the evaporator or exit from the filter drier. It often looks like a thin line running along a thicker return line.
Location in the refrigeration circuit
To understand exactly where the capillary tube is located, it is necessary to imagine the general path of refrigerant movement. It is always located between two key components: the filter drier and the inlet to the evaporator. A filter drier is a small metal cylinder, often painted black or gray, that sits just after the condenser (the grill at the back of the refrigerator).
The layout looks like this: the compressor forces hot gas into the condenser, where it cools and turns into liquid. This liquid enters the filter, is cleaned of moisture and impurities, and then goes directly to capillary tube. This is where the sharp drop in pressure occurs. After passing through the capillary, the mixture of liquid and gas enters the evaporator, where the process of active boiling and heat absorption occurs.
In old models of refrigerators, for example, in Soviet ZIL or early ones Biryusa, a capillary tube was often laid along the perimeter of the door or inside the walls of the case, glued to the metal. In modern units, it is most often enclosed in a separate channel inside the thermal insulation or taped to the suction tube of the compressor to increase energy efficiency.
Hidden gasket in No Frost
In refrigerators with the No Frost system, capillary the tube often goes directly to the evaporator unit, which is hidden behind a plastic panel in the freezer. It is impossible to get to it without partially disassembling the camera and removing the fan.
When searching for an element, pay attention to the soldering points. On one side the capillary is sealed into the filter drier, on the other - into the expansion manifold of the evaporator. These connection points are critical areas where microcracks or blockages most often occur.
Principle of operation and physical properties
The main function of the capillary tube is to create hydraulic resistance. Passing through a narrow hole, liquid freon experiences strong friction against the walls of the tube. This resistance causes the pressure at the outlet of the tube to drop sharply and the temperature of the substance to decrease. This process is called throttling.
Unlike thermostatic valves (TEV), which are used in industrial installations and can change the cross-section of the passage channel, the capillary tube has a constant diameter. It has no moving parts and works solely due to the physical properties of fluid flow. Throughput pipes are calculated by engineers with an accuracy of a millimeter, since the pressure balance in the system depends on this.
| Parameter | Value/Description | Impact on operation |
|---|---|---|
| Internal diameter | 0.6 - 1.5 mm | Determines the volume of passing freon |
| Length | 1.5 - 4.5 m | Creates the necessary resistance to flow |
| Material | Copper M1, M2 | Provides ductility and heat transfer |
| Operating pressure | Up to 25 atm (at inlet) | Requires high soldering strength |
Interestingly, when the compressor stops, the pressure in the discharge and suction lines through the capillary tube are leveled out. This makes it easier to restart the engine, since it does not need to overcome a large pressure difference immediately after starting.
Typical faults: blockages and mechanical damage
Despite the simplicity of the design, the capillary tube is susceptible to two main types of faults: mechanical damage and blockage. Mechanical damage often occurs due to vibration or corrosion if the refrigerator has been used in a damp area. At the site of damage, you will hear the hiss of escaping gas and see traces of oil.
Clogging is a more insidious problem. It can be caused by moisture entering the system (formation of an ice plug) or the presence of solid particles of oxides and dirt (paraffin or mud blockage). Symptoms of a clog are that the refrigerator stops freezing, and the compressor works continuously, trying to gain temperature.
- ❄️ Ice plug: Occurs when moisture gets in, often thaws itself after a long period of inactivity, but comes back again.
- 🛑 Mud blockage: Requires professional blowing nitrogen or replacing the filter drier.
- 🔨 Kink: Mechanical squeezing of the tube during installation, blocking the flow of freon.
You can diagnose a blockage by touching filter drier. If it is hot, but the capillary tube after the filter is cold (or covered with frost), then the flow is blocked. Normally, the filter should be warm, but not hot, and the tube after it should be at ambient temperature before entering the evaporator.
⚠️ Attention: An attempt to clean the capillary tube with water or chemical solvents at home without evacuation of the system will lead to complete destruction of the compressor due to moisture and acid getting inside the windings.
To remove serious blockages, technicians use high-pressure nitrogen pressing or ultrasonic cleaning, but it is often easier and more reliable to replace a section of the tube with a new one, observing the exact geometric dimensions.
The process of replacing and restoring the system
Replacing a capillary tube is a complex repair process that requires specialized equipment. It is not limited to simply soldering copper. The procedure begins with the complete removal of old refrigerant and dismantling the faulty element. It is important to carefully remove the tube from the filter and evaporator without damaging the adjacent lines.
After installing a new tube, which must be identical to the old one in length and diameter, a mandatory vacuum procedure is performed. All air and moisture vapor must be removed from the system. Only after creating a deep vacuum is the new refrigerant charged strictly according to the weight indicated on the refrigerator nameplate.
☑️ Check after replacement
When soldering new connections, it is necessary to use solder with a melting point above 600 degrees and be sure to use flux, but its residues must be carefully removed to prevent corrosion. Often, when replacing a capillary, the filter-drier is also changed, since the old one could already be saturated with moisture and cause re-clogging.
Differences in different types of refrigerators
The design of the capillary system may differ depending on the type of refrigerator. In single-compressor models with one cooling circuit, there is only one tube, and it serves both the refrigeration and freezer compartments. In dual-circuit systems (for example, in some models LG or Whirlpool), two capillaries or one with a flow switching solenoid valve can be used.
In refrigerators with a system No Frost the capillary tube is often shorter, but requires more accurate calibration, since the evaporator is hidden and blown by a fan. In drip systems ("crying evaporator"), the length of the capillary can be longer to ensure uniform distribution of the refrigerant along the back wall of the chamber.
It is also worth noting the difference when using different types of refrigerants. For R134a and R600a (isobutane) capillaries with different characteristics are required. Isobutane is more explosive and requires less substance, so the diameter and length of the tube for it will differ from those used in old refrigerators. Is it possible to replace the capillary tube with a tube of a different diameter? R12.
Is it possible to replace the capillary tube with a tube of a different diameter?
It is strictly not recommended. Changing the diameter even by 0.1 mm dramatically changes the throughput. This will lead to an imbalance of pressure: the compressor will work with overload or, conversely, with underload, which will cause its rapid failure.
Why does the capillary tube sometimes freeze to the evaporator?
This is a normal phenomenon at the exit point from the capillary, where evaporation begins. However, if frost or ice covers the tube for a long distance before entering the evaporator, this indicates a blockage or lack of freon.
How to determine that the capillary tube is pinched?
When pinched (mechanical narrowing), the refrigerator will operate with severe overheating of the condenser, and the suction pressure will be abnormally low. Visually, the place of pinching is often visible by a characteristic dent in the copper.
How long does a capillary tube last?
The service life of this element is practically unlimited if the system is sealed and there is no moisture in it. Usually it fails only with mechanical damage or secondary clogging due to combustion of the compressor.
Is it necessary to warm up the capillary during defrosting?
No, you cannot heat the capillary tube with an open fire to defrost the ice inside. This can lead to solder depressurization or damage to the copper structure. Defrosting should occur naturally.