The capillary tube is the heart of the cooling system of any household refrigerator, responsible for creating the necessary pressure difference between the condenser and the evaporator. It is this thin copper element that regulates the flow of refrigerant, turning it from liquid to gas, which allows the food inside the chamber to remain fresh. Failure or clogging of this part often leads to the fact that the compressor works without interruption, but the cold is not produced, requiring immediate intervention from a specialist or competent home repairs.
Selecting the right tube is not just a matter of buying copper of the required diameter, but a complex engineering task that requires taking into account many parameters, such as the power of the compressor, the type of freon used and the volume of the evaporator. An error in calculating the length or diameter can lead to overheating of the motor, insufficient cooling, or even freezing of the pipelines, so the selection process must be approached with the utmost care. In this article we will analyze all the nuances that will help you accurately determine the required characteristics for your refrigerator model.
The principle of operation and the role of the capillary tube
The refrigeration cycle is based on the ability of the refrigerant to change its state of aggregation, absorbing and releasing heat, and the capillary tube acts as a throttling device. It creates hydraulic resistance, due to which the pressure at the inlet to the evaporator drops sharply, causing freon to boil at low temperatures. Length and internal diameter the tubes are selected by the manufacturer in such a way as to ensure a mass balance of the refrigerant circulating in the circuit.
If the resistance is too high due to excessive length or small diameter, the compressor will work with overload, trying to push freon, which will lead to its overheating and possible failure. On the other hand, a tube that is too short or wide will not create a sufficient pressure drop, and the refrigerant will not have time to completely evaporate, entering the compressor in a liquid state, which causes water hammer. Precise calibration This element is critical to the energy efficiency and durability of the unit.
Modern Refrigerator models may use tubes with different characteristics depending on the energy class and type of refrigerant. For example, environmentally friendly freons, such as R600a, often require tubes of smaller diameter compared to traditional R134a. Understanding these differences helps to avoid mistakes when replacing components.
⚠️ Attention: The capillary tube is a disposable element in the factory assembly, and its reuse after dismantling is strictly prohibited. Microscopic contamination or deformations inside the copper can disrupt the laminar flow of refrigerant.
Key parameters for selecting an analogue
When looking for a replacement for a failed tube, the first thing you need to pay attention to is the markings on the compressor itself or in the technical documentation of the refrigerator. The main parameters are the internal diameter, which usually varies from 0.5 to 1.0 mm, and the length, which can reach several meters depending on the power of the system. Internal diameter is the most critical parameter, since even a small deviation of hundredths of a millimeter drastically changes the throughput.
The length of the tube is selected experimentally or using reference tables, since it depends on the specific design of the heat exchanger and the conditions for heat removal. Standard practice involves the use of tubes ranging from 2 to 4 meters in length, however, this parameter may differ in some industrial or specific household models. It is also important to take into account the material used: only seamless copper tube high purity is used, annealed to impart elasticity.
Another important aspect is the condition of the inner surface of the tube, which must be absolutely clean and free of grease. The entry of moisture or mechanical particles into the circuit can lead to the formation of ice plugs or acids that destroy the system from the inside. Therefore, when selecting, make sure that the tube is supplied in a sealed package with plugs at the ends.
Correspondence table of diameters and refrigerants
The choice of tube diameter directly depends on the type of refrigerant used in your refrigerator model, since different gases have different viscosity and density. Below is a reference table that will help you navigate the initial selection parameters for the most common types of household refrigerators.
| Refrigerant type | Recommended internal diameter (mm) | Approximate length (m) | Type compressor |
|---|---|---|---|
R134a |
0.66 - 0.71 | 2.5 - 3.5 | Piston |
R600a |
0.50 - 0.60 | 2.0 - 3.0 | Piston/Inverter |
R12 (old models) |
0.70 - 0.80 | 3.0 - 4.0 | Piston |
R404a (showcases) |
0.80 - 0.90 | 3.5 - 4.5 | High-performance |
The data in the table are averages and may vary depending on the specific model and year of manufacture of the refrigeration equipment. To accurately determine the parameters, you must check the manufacturer's service manual or use the recalculation method if the original tube was lost or severely deformed. Selection accuracy diameter affects the ability of the system to maintain a given temperature.
Why the R600a needs a smaller one diameter?
Isobutane (R600a) has a high molecular weight and excellent refrigeration properties, which allows the use of tubes of a smaller cross-section to create the necessary throttling, reducing the overall volume of filling the system.
Methods for calculating the length of a capillary tube
Determining the exact length of the tube often becomes the most difficult part of the repair, especially if the factory markings are missing or damaged. There are several calculation methods, among which the most common is the one-to-one replacement method, when the new tube is cut to the same length as the dismantled one, provided that its diameter matches the original. However, if the original is lost, the pressure selection method is used.
The essence of the method is to connect a pressure gauge station to the compressor discharge pipe and set the expected length of the tube. The compressor starts and the technician watches the pressure gauge, gradually shortening the tube until the pressure reaches the design value for the type of compressor and refrigerant. This process requires high qualifications and the availability of special equipment.
- 🔧 Prepare a piece of copper tube about 4 meters long with an internal diameter corresponding to the type of freon.
- 🔧 Connect one end of the tube to the discharge pipe of the compressor through the pressure gauge fitting.
- 🔧 Start the compressor and record the discharge pressure after the indicators have stabilized (usually 10-15 minutes).
- 🔧 If the pressure is higher than the nominal one, gradually cut off 10-20 cm of tubes, repeating the measurements until the desired value is obtained.
Optimal discharge pressure for household refrigerators using R134a are usually 8-10 bar, and for R600a - 6-8 bar, but always look at the compressor data sheet for exact numbers.
Installation and soldering technology of connections
After successful selection of length and diameter, the installation stage begins, which requires adherence to strict technology for soldering copper connections. Before starting work, you must make sure that the ends of the tubes and pipes are clean, degreased and free of oxides, since the quality of soldering directly affects the tightness of the system. Use only copper-phosphorus solders copper-to-copper joints, as they provide a strong and reliable seam without the need for additional fluxes.
The soldering process involves heating the joint with a torch until cherry-colored, after which solder is introduced into the contact area, which should flow into the gap under the action of droplet forces. It is important not to overheat the tube so that it does not burn out, especially given the thin walls of the capillary. After the seam has cooled, it is necessary to carry out a visual inspection for the presence of holes or unsoldered areas.
☑️ Checklist for soldering a capillary tube
Particular attention should be paid to the insertion of the capillary tube into the filter drier. The tube must go inside the filter to a certain depth (usually 15-20 mm), but in no case rest against the bottom, as this will block the flow of refrigerant. Filter drier also must be replaced whenever the circuit is opened, since it loses its properties when in contact with atmospheric air.
⚠️ Attention: When soldering near plastic elements or insulation, use a damp cloth or heat-protective screens to avoid damaging adjacent components of the refrigerator with an open flame of a burner.
Common mistakes and how to make them elimination
Even experienced craftsmen can make mistakes when replacing the capillary tube, which leads to incorrect operation of the refrigerator. One of the most common problems is an insufficient tube length, which causes increased pressure in the evaporator and insufficient cooling, or vice versa - a tube that is too long, creating excessive resistance and overheating of the compressor. Diagnosis of such problems is made by the temperature of the evaporator and the current consumption of the motor.
Another common mistake is the use of a tube of the wrong diameter, which is almost impossible to fix without completely replacing the element. Also, a violation of the soldering technology often occurs, leading to the formation of an oxide film inside the tube, which over time can come off and clog the narrow section of the capillary. Hydraulic hammer when filling or improper evacuation can also damage the system.
- 🔥 Overheating of the zone soldering, leading to deformation of the tube and a change in its internal diameter.
- 💧 Moisture entering the circuit due to insufficient evacuation time, which causes freezing of the capillary.
- 🛑 Using a tube with mechanical damage or creases that disrupt the freon flow.
To eliminate most errors require re-opening the circuit, replacing the filter-drier and recalculating the length of the capillary tube. In some cases, it may be necessary to replace the compressor itself if it has been operating in abnormal mode for a long time. Error prevention lies in strict adherence to technology and the use of proven materials.
Checking performance after replacement
After installing a new capillary tube and filling the refrigerator with refrigerant, it is necessary to conduct a comprehensive check of the system's performance. The first indicator of success is uniform cooling of the entire surface of the evaporator, without localized warm spots or excessive freezing in the tube inlet area. The compressor must operate cyclically, turning on and off at regular intervals corresponding to the set temperature.
It is also important to control the temperature of the compressor housing: it should not exceed 70-80 degrees Celsius during prolonged operation. If the motor gets hotter, this may indicate that the discharge pressure is too high or the capillary tube is not long enough. Using a thermal imager or contact thermometer helps to accurately diagnose the thermal operating conditions of components.
⚠️ Attention: If, after replacing the tube, the refrigerator starts working, but after a few hours it stops cooling, an ice plug may form in the capillary due to residual moisture - repeated evacuation and filter replacement are required.
The final stage of the test is to check for the absence of refrigerant leaks in the soldering areas using a soap solution or an electronic leak detector. Even a microscopic leak will lead to loss of performance and compressor failure over time. Having ensured that the temperature regime is tight and stable, the replacement of the capillary tube can be considered successfully completed.
Is it possible to use a steel tube instead of a copper one?
The use of a steel tube is highly not recommended, since steel has poorer thermal conductivity, is susceptible to corrosion from the inside and is more difficult to solder in the field. Copper provides better heat exchange with the environment, which is important for the operation of the capillary, and is easier to process.
How to determine that the capillary tube is clogged?
The main signs of a clog: the compressor runs constantly, but does not cool; the filter drier can be hot or, conversely, covered with frost; when the system depressurizes, gas under pressure does not come out of the tube or comes out very weakly.
Is it necessary to purge the new tube before installation?
Yes, the new tube must be purged with dry nitrogen or inert gas to remove possible chips, dust or oxides remaining after production and cutting. This will prevent the system from clogging again immediately after startup.
Does the room temperature affect the operation of the selected tube?
Yes, the ambient temperature affects the condensation pressure and, therefore, the capacity of the capillary. Calculations and selection are usually carried out for standard room temperature (+25°C), and significant deviations may require length adjustments.