Optimal length of the capillary tube in the refrigerator: calculation, selection and nuances

A capillary tube is one of the key elements of the refrigeration circuit, on which the efficiency of operation directly depends compressor and temperature stability in the chambers. Its incorrect length can lead to overheating of the motor, insufficient cooling or even system failure. But how to determine exactly what footage is needed for your model? After all, there is no universal answer: the parameters depend on the type of refrigerant, compressor power, route length and even climatic operating conditions.

In this article we will figure out how to calculate the optimal length of the capillary tube for refrigerators of different brands (Indesit, Atlant, Samsung, LG etc.), what formulas the craftsmen use, and what happens if you make a mistake with the footage. You will also find correspondence tables for popular models and step-by-step instructions for replacement - taking into account nuances that are not written about in standard manuals.

What is a capillary tube and why is it needed?

A capillary tube is a thin copper or aluminum channel with an internal diameter 0.5–1.2 mm, which performs two key functions:

• 🔹 Refrigerant throttling —reducing the freon pressure in front of the evaporator, which ensures its boiling and heat absorption.
• 🔹 Flow adjustment —maintaining stable refrigerant flow regardless of the load on system.

Unlike a thermostatic valve (TRV), the capillary tube has no moving parts, which makes it more reliable, but also more sensitive to precision selection of length. If the tube is too short, the freon does not have time to expand sufficiently - the compressor is overloaded. If it is too long, the refrigerant loses pressure ahead of time, and the refrigerator does not freeze well.

In modern refrigerators (No Frost, Low Frost, inverter models), the capillary tube is often combined with a filter-drier, forming a single unit. In old Soviet units (for example, "ZIL" or "Minsk") it could be a separate element soldered to the capacitor.

What determines the length of the capillary tube?

The length of the tube is not selected "by eye" - it is calculated taking into account several parameters:

1. Refrigerant type. For R134a and R600a (isobutane) require different lengths due to different viscosity and heat capacity. For example, R600a needs a shorter tube than R12 (obsolete freon).
2. Compressor power. The higher the motor performance (measured in W or BTU), the longer the tube can be - but only up to a certain limit.
3. Length of the circuit route. If the condenser and evaporator are located far from each other (for example, in refrigerators Side-by-Side), the tube must compensate for the hydraulic resistance.
4. Tube diameter. Standard values: 0.6 mm, 0.8 mm, 1.0 mm. The thinner the tube, the shorter it should be (other things being equal).
5. Temperature conditions. For freezer compartments (-18°C and below) the tube is shorter than for refrigeration compartments (+4...+6°C).

Also influence climatic conditions: in hot climates (for example, in the Middle East), manufacturers can install longer tubes to compensate for the increased load to the condenser.

Formula for calculating the length of a capillary tube

For an approximate calculation, experts use an empirical formula:

L = (Pk × Kf) / (D² × ΔT)

Where:

• L — tube length in meters;
• Pk — compressor power in W;
• Kf — coefficient refrigerant (R134a = 1,0; R600a = 0,85; R290 = 0,9);
• D — internal diameter of the tube in mm;
• ΔT — temperature difference between the condenser and the evaporator (usually 30–40°C).

Example: for a refrigerator Atlant MXM-1708 with compressor 90 W, refrigerant R600a and tube diameter 0.7 mm:

L = (90 × 0.85) / (0.7² × 35) ≈ 4.6 meters

However, this formula gives approximate the exact length is selected experimentally or according to the manufacturer's tables. data-i="126">with the system Samsung with the system No Frost the tube is often 20–30% shorter than in drip models of the same power.

Why you can’t use a tube with a reserve"

A long tube increases hydraulic resistance, due to which the compressor wears out, and the temperature in the chamber becomes unstable. In some cases, this can lead to icing of the evaporator and emergency protection.

Table of standard lengths for popular models

The following is a table with typical values for refrigerators of different brands. Data are based on service manuals and may vary slightly depending on. modifications.

Important: if your model has an inverter compressor, the length of the tube can be 10–15% shorter than in conventional refrigerators of the same power. This is due to a smoother adjustment of motor speed.

How to measure and replace the capillary tube?

If you decide to replace the tube yourself, follow this algorithm:

Turn off the refrigerator and defrost it at 12+ hours|

Drain the refrigerant through the service port (a vacuum pump is required)|

Unsolder the old tube from the filter drier and condenser|

Select a new tube according to diameter and length (see table above)|

Solder the tube, avoiding overheating of the copper (use a torch with a flame regulator)|

Fill the system with refrigerant and check the tightness with a soap solution-->

For soldering, use (solder with a melting point not higher 250°C, so as not to damage the compressor insulation. After replacement, be sure to:

• 🔧 Check the pressure in the system with a pressure gauge (norm for R600a: 0.1–0.3 MPa at suction).
• ⚡ Vacuum for 15–20 minutes to remove moisture.
• ❄️ Turn on the refrigerator and check the temperature after 6–8 hours.

If after replacement the compressor runs non-stop or ice forms in the chamber, it means that the tube has been selected wrong too short or long. In this case, you will have to repeat the procedure with a different length.

What will happen if the length of the tube wrong?

Errors in selecting the length lead to serious problems:

⚠️ Attention: If the tube is short, the compressor will operate in overload mode, which will lead to its overheating and reduced service life. Characteristic signs: constant hum of the motor, hot body, activation of the thermal relay.

⚠️ Attention: If the tube long, the refrigerant does not have time to completely evaporate in the circuit. This manifests itself as insufficient cooling, freezing of the evaporator or cyclical shutdown of the refrigerator at short intervals.

In both cases, electricity consumption increases by 15–30%and the risk of breakdown increases in 2-3 times. This is especially critical for inverter models (Samsung Digital Inverter, LG Smart Inverter), where the compressor is not designed for long-term peak loads.

In some cases, the wrong length of the tube can lead to hydraulic shock - when liquid freon enters the compressor. This almost always ends with irreversible damage motor.

How to choose a tube for non-standard refrigerators?

If your refrigerator:

• 🏠 Built-in (for example, Liebherr or Bosch),
• 🌡️ Medical (for storing vaccines),
• 🍷 Wine (with zone +10...+14°C),
• 🚚 Automotive (on 12/24 V),

then standard tables may not be suitable. In such cases:

1. Look for data in service manual (for example, for Liebherr IK 3560 the length of the tube is indicated on the refrigeration circuit diagram).
2. Contact the official service center brand - they can provide exact parameters according to the serial number.
3. Use dynamic calculation taking into account the actual pressure in the system (a manometric manifold is required).

For car refrigerators (Dometic, Indel B) the length of the tube is often shorter by 30–40%than in household models, due to the compactness of the system and the use of refrigerants such as R134a or R404a.

FAQ: Frequently asked questions about capillary tubes

Is it possible to shorten the capillary tube if it is too long?

Yes, but with reservations. You can shorten it no more than 10–15% from the original length, the pressure balance will be disrupted, and the compressor will wear out. data-i="226">Clean and solder the edge of the tube.

• Strip and seal the edge of the tube.
• Blow it with nitrogen to remove sawdust.
• Check the system for leaks.

How to determine the diameter of the tube without a micrometer?

If you don’t have accurate ones at hand tools, use caliper or even a regular ruler with magnification (for example, through a magnifying glass). Measure outer diameter and subtract twice the wall thickness (usually 0.1–0.15 mm for copper tubes). ≈ 1.0 mm, then internal ≈ 0.7–0.8 mm.

What is the difference between tubes for R134a and R600a?

Tubes for R600a (isobutane) are usually thinner and shorterthan for R134a, due to the higher thermal conductivity of the refrigerant. For example, when. same compressor power:

• For R134a: diameter 0.8 mm, length 5.0 m.
• For R600a: diameter 0.6 mm, length 4.0 m.

Also tubes for R600a should be cleaner —this refrigerant is sensitive to moisture and contaminants.

Is it possible to use an aluminum tube instead of a copper one?

No, it is It is strictly prohibited. Aluminum oxidizes upon contact with refrigerants, which leads to:

• Clogging of the circuit with corrosion products.
• Leakage of freon through microcracks.
• Fire hazard (aluminum can spark when soldered).

An exception is some industrial systems that use special alloys, but this is unacceptable in household refrigerators.

How to check that the tube is clogged?

Signs of a clogged capillary tubes:

• The compressor works, but the refrigerator does not cool.
• The condenser (grid at the back) remains cold.
• You can hear gurgling or "squelching" in the circuit.

For diagnostics:

1. Turn off the refrigerator and let it stand 1 hour.
2. Connect the pressure gauge to the service port. If the suction pressure (low side) is close to 0 —the tube is clogged.