The capillary tube in the refrigerator is the heart of the cooling system, performing the function of a throttle that regulates pressure and flow refrigerant. It is thanks to this thin copper element that freon moves from a state of high pressure to low, providing the necessary cooling effect in the evaporator. Failure or clogging of this component leads to a complete stop of the cycle, which requires immediate intervention and qualified repairs.
If you are faced with the need for replacement, it is important to understand that there is no universal answer to the question “what to replace with” in the everyday sense. You will need not just a similar part, but an exact reproduction of the hydraulic resistance of the system. Incorrect selection of diameter or length will lead to the compressor working with overload, and the temperature in the chambers will not drop to the required values.
In this article we will analyze the technical nuances of selecting material, methods for calculating length and installation technology. You will learn why you should not use random scraps of copper tubing and how to properly solder so that the system will work for years. Attention to detail during the preparation phase will save you time and money in the future.
Design and purpose of a capillary choke
A capillary tube is a long piece of copper pipe with a very small internal diameter, usually ranging from 0.5 to 2.0 millimeters. In household refrigerators, a tube with a diameter of 0.6–0.8 mmis most often used. Its main task is to create resistance to the flow of liquid refrigerant leaving the condenser and to ensure a pressure difference between the high-pressure and low-pressure parts of the circuit.
The principle of operation is based on the physics of liquid: passing through a narrow hole, freon loses pressure and partially evaporates, turning into a mixture of liquid and gas. This process occurs immediately before entering the evaporator. If the diameter is too large, liquid freon will enter the compressor, causing hydraulic shock, which is fatal to the piston group.
⚠️ Attention: An attempt to replace the capillary tube with a larger diameter tube without recalculating the length will lead to instant failure of the compressor. Water hammer destroys valves.
The length of the element is also critically important. In the factory, it is calculated to the nearest centimeter for a specific compressor model and refrigerant type. Standard length varies within 2–5 meters, rolled into a spiral for compactness. Increasing the length increases resistance, reducing the performance of the system, and decreasing it, on the contrary, overloads the motor.
Why copper?
Copper is used due to its ductility, high thermal conductivity and the ability to be easily soldered with soft solders. Steel or aluminum tubes are not suitable due to the complexity of the hermetic connection and corrosion activity in the environment of freon and oil.
Criteria for selecting an analogue: diameter and material
When the question arises of how to replace a failed element, the first parameter to search for is the internal diameter. The outer diameter may vary depending on the wall thickness, but it determines the throughput. For home refrigerators, the standard is the range of 0.66–0.91 mm. internal section determines throughput. For home refrigerators, the standard range is 0.66–0.91 mm.
The replacement material can only be a copper tube grade M or MM (soft, annealed). The use of air conditioning or water pipes is not permitted as they have a different grain structure and may not withstand the cyclic vibrations of the compressor. In addition, the cleanliness of the internal surface is important: any oxides or dirt will lead to a new blockage.
When purchasing material, pay attention to the condition of the surface. The tube must be perfectly smooth, without dents, kinks or signs of oxidation. If you are using a piece from an old refrigerator, it must be thoroughly washed with solvent and purged with nitrogen under pressure.
Calculation of length and correspondence table
Determination of the exact length is the most difficult stage of replacement. Since factory data is often unavailable, craftsmen use empirical methods or lookup tables. The length directly depends on the power of the compressor and the type of refrigerant used (R134a, R600a, R12).
For an approximate calculation, you can use the rule: for every 100 W of compressor power, a certain resistance is required, which is expressed in meters of a tube of a specific diameter. However, in order not to guess, it is better to focus on reference data for common household models.
| Refrigerant type | Internal diameter (mm) | Approximate length (m) | Compressor power |
|---|---|---|---|
| R134a | 0.66 - 0.70 | 2.5 - 3.5 | up to 150 W |
| R600a | 0.70 - 0.80 | 3.0 - 4.5 | up to 120 W |
| R12 (old) | 0.66 - 0.80 | 2.0 - 3.0 | up to 180 W |
| R404a (trade) | 1.00 - 1.20 | 1.5 - 2.5 | up 400 W |
| Universal | 0.80 - 0.90 | 4.0 - 5.0 | medium |
There is a selection method “by ear” and by pressure, which is used by experienced craftsmen. A pressure gauge station is connected to the compressor, and the length of the tube is gradually reduced (cut off by 10-20 cm) until the desired suction pressure is achieved. This method requires a vacuum pump and pressure gauges.
If you replace the capillary with a more modern analogue with a different diameter, the length will have to be recalculated in proportion to the fourth power of the change in diameter (Poiseuille's curve), which makes experiments with diameter extremely risky.
Replacement technology: step-by-step instructions
The process of replacing a capillary tube requires not only materials, but also specialized equipment. You will need a torch (gas or oxyacetylene), copper solder, flux, vacuum pump and a gauge manifold. Without evacuation of the system, refueling is impossible.
The first step is to dismantle the old element. The tube is carefully unsoldered from the filter drier and the entrance to the evaporator. It is important not to damage the thin evaporator tubes, which are often made of aluminum and welded to a steel plate. The place where copper and steel are soldered requires special care and the use of special solders.
- 🔧 Prepare a new piece of copper tube of the calculated length, clean the ends from oxides.
- 🔥 Warm up the junction of the filter and the tube, evenly distributing the flame so as not to burn through the thin walls.
- ❄️ After soldering, be sure to vacuum the system for 30-40 minutes to remove moisture and air.
When soldering a new capillary into the filter drier, the immersion depth should be 12–15 mm. If you insert the tube deeper, it may rest against the filter mesh and block the freon flow. If less, there will be a risk of leaks due to vibration.
☑️ Check before soldering
Soldering and working with the filter-drier
One of the most critical aspects of the replacement is the soldering of the copper-steel connection (capillary and filter). Steel and copper have different melting points and thermal conductivities. For a high-quality connection, it is necessary to use silver-containing solder (for example, PSR-15 or PSR-45) and a flux intended for dissimilar metals.
The filter drier is a disposable element. If there is any depressurization of the circuit, even short-term, it must be changed. Inside there is zeolite, which instantly absorbs moisture from the air. If you leave the old filter, the moisture will freeze in the capillary, forming an ice plug, and the refrigerator will stop freezing.
⚠️ Attention: The filter drier cannot be stored in an open package for more than 10 minutes. It must be soldered immediately after removal from the sealed bag.
The soldering process must take place quickly so as not to overheat the filter housing. Heat dissipation can be ensured by wrapping the filter housing with a wet rag or using a radiator clamp. After cooling, the seam is checked for leaks by blowing with a soap solution under nitrogen pressure.
Diagnostics of errors and common problems
After assembling the system and filling with refrigerant, it is necessary to carry out diagnostics. The main indicator of proper operation is uniform cooling of the evaporator and the absence of freezing of the capillary tube outside the refrigeration chamber. If the tube becomes covered with frost immediately after the filter, this is a sign of blockage or too small a diameter.
A common mistake is insufficient vacuuming. The remaining air in the system increases the condensation pressure, which causes the compressor to wear out. You can check this by the temperature of the condenser: it should be hot, but not red-hot, along its entire length.
It is also worth paying attention to noise. A humming, gurgling or whistling sound may indicate that the capillary length is incorrect. A tube that is too long will create excess pressure in front of it, and the freon will be “pushed” in jerks, creating characteristic sounds.
- 📉 Low suction pressure is a sign of a blockage or a tube that is too long/narrow.
- 📈 High discharge pressure - indicates a short/wide tube or the presence air.
- 💧 Condensation on the compressor suction tube - risk of water hammer, the capillary cross-section is too large.
In some cases, especially in No Frost refrigerators, a blockage may not be caused by a breakdown, but by oil getting into the circuit due to prolonged parking in a horizontal position. Before replacing the tube, make sure that the problem is in the throttle and not in contamination of the system.
Can a capillary from another refrigerator be used?
Can only be used if the internal diameter and length are exactly the same. However, given the difference in compressor models and freon types, this is a lottery. It is better to calculate and make a new section than to guess with a used part.
What are the dangers of independent replacement without a vacuum sealer?
The absence of a vacuum sealer will result in air and moisture remaining in the system. The moisture will freeze in the capillary, blocking the freon flow. The air will increase pressure, increase the load on the compressor and reduce cooling efficiency. The lifespan of the refrigerator will be reduced significantly.
How to determine that the capillary is clogged?
Signs: the compressor runs constantly, but there is no cold; the condenser (grid at the back) is cold or warm only at the compressor; the capillary tube may be covered with frost at the entrance to the evaporator, and then at room temperature.
Is it necessary to change the oil in the compressor when replacing the tube?
In most household cases, a complete oil change is not required if the compressor was working normally. It is enough to replace the filter drier. However, if the system has been open for a long time or moisture has entered it, it is better to replace the oil with fresh oil corresponding to the type of freon (mineral or polyester).
Which solder is best to use for copper?
For a copper-copper connection, copper-phosphorus solders (for example, PMF-7) without flux are sufficient. To connect copper-steel (with a filter), you definitely need silver solder (PSR) and flux, since phosphorus solders provide a fragile connection with steel.