Faced with the need to replace compressor a household refrigerator, many amateur craftsmen find themselves confused, looking at the copper tubes protruding from the motor housing. Outwardly, they may appear identical, but their diameter, purpose and location are strictly regulated by engineering logic. An error in determining which tube to solder where can lead to instant failure of the new unit or a complete lack of cold in the chamber. Therefore, understanding the principles of operation refrigeration circuit is critically important before starting work.
In a standard single-compressor refrigerator there are usually three main copper outlets, not counting the process pipe for charging freon. Two of them have noticeably different diameters, and the third, the capillary tube, is often thinner than the others and can be wound in a spiral or hidden in insulation. The master's task - accurately identify the suction line, discharge line and inlet capillary. An incorrect connection will lead to the fact that the system will not be able to create the required pressure, and the refrigerant will not circulate through the system.
In this article we will look in detail at how to visually and tactilely determine the purpose of each tube, what tools are required for high-quality installation and what typical mistakes are made newbies. We will look at the physical differences in diameters, explain the principle of operation piston group and give clear instructions for preparing connections. The diameter of the suction tube is always greater than the diameter dischargewhich is the first and main guideline for visual inspection.
Principal diagram of the operation of a refrigeration unit
To understand where to put the tubes, you need to briefly refresh your memory of the refrigerant circulation cycle. The compressor works like a pump that drives freon in a vicious circle, changing its state of aggregation. First, low-pressure freon gas enters the compressor, where it is compressed and heated. Then it exits under high pressure into the condenser (the radiator at the back of the refrigerator), where it cools and turns into liquid.
After the condenser, liquid freon passes through a filter drier and enters the thinnest capillary tube. This is where the sharp drop in pressure occurs. After leaving the capillary, the refrigerant enters the evaporator (inside the freezer), where it boils at a low temperature, actively absorbing heat from the refrigerator chambers. After the evaporator, the already gaseous, but cold freon returns to the compressor again, closing the cycle.
Understanding of this process dictates the connection logic: one tube should take gas from the evaporator (suction), the other should throw the compressed gas into the condenser (discharge). The third, thinnest, supplies liquid freon from the condenser. Violation of the sequence, for example, connecting the discharge to the capillary, will create excess pressure, which can rupture the thin walls of the evaporator or lead to breakdown of the compressor valves.
⚠️ Attention: Never turn on the compressor “for air” without connecting to the system or with open tubes for more than 30-60 seconds. This can lead to overheating of the windings and breakdown of the insulation, since the freon in the system also performs the function of cooling the motor.
It is important to note that in modern inverter models and refrigerators with the system No Frost the principle remains the same, but the requirements for system cleanliness and soldering accuracy increase many times over. Any microscopic moisture or debris can clog the capillary, so sealing and vacuuming are mandatory steps that should not be forgotten.
Visual and tactile diagnostics of tubes
The first way to determine the purpose of the tubes is a careful inspection. The housing of most modern compressors (brands Atlant, Danfoss, Secop, Embraco) has arrows or letter designations stamped on them. An arrow pointing away from the tube indicates discharge, and an arrow pointing toward the tube indicates suction. You can often find markings in Latin letters: D (Discharge) for discharge and S (Suction) for suction. The capillary tube is often not marked on the compressor body itself, since it is part of the external circuit.
If the marking is worn out or missing, include a visual assessment of the diameter in the work. The suction tube always has the largest diameter, usually about 8-10 mm or more, since the gas returning from the evaporator has a low density and occupies a large volume. The discharge tube is thinner, approximately 6-8 mm in diameter, since the compressed gas (or liquid at the beginning of the condenser) takes up less space. The capillary tube is the thinnest, its diameter often does not exceed 1.5-2 mm.
The tactile testing method only works if the old compressor is still partially functioning or has retained remnants of freon under pressure. When turned on for a short time (literally for 2-3 seconds), a strong air flow will be felt from the discharge tube, which can even blow out the lighter’s flame. Air, on the contrary, will be sucked in from the suction tube, which can be checked by placing your finger near the hole - it will “stick” slightly.
- 🔍 Diameter: The thickest pipe is always the inlet (suction), the middle one is the outlet (discharge), the thinnest is the entrance to the capillary.
- 🏷️ Marking: Look for embossed arrows or letters S/D on the metal casing next to the nozzles.
- 🌬️ Air flow: During a short start, it blows from the discharge tube, and sucks to the suction tube.
Sometimes masters use the “by ear” method, but it is ineffective for beginners. A more reliable way is to check the location of the tubes relative to the structure. The suction tube is often (but not always) located closer to the edge of the housing or has a more noticeable bend just at the outlet. However, you should not rely only on geometry, since the layout may differ from different manufacturers (Whirlpool, Bosch, Indesit).
Role and search for a capillary tube
The capillary tube is the “heart” of throttling in the system. It is a long (from 2 to 6 meters) copper tube of very small diameter, rolled into a coil. Unlike the thick lines leading to the compressor, the capillary is often hidden in a trough along the housing or taped to the evaporator tube for heat exchange. Finding its beginning is a key task during assembly.
The capillary tube is always connected to the outlet of the filter-drier. Therefore, the connection chain looks like this: Compressor (discharge) → Condenser (radiator) → Filter drier → Capillary → Evaporator → Compressor (suction). If you see a thin copper tube entering a thick evaporator pipe or frozen into an aluminum plate, this is a capillary. It should not be bent or compressed, since the internal cross-section is critical for creating a pressure differential.
When replacing a compressor, the old capillary tube is often cut off, and then the question arises: how to connect a new one? In professional repairs, the capillary is replaced entirely along with the circuit, but sometimes a joining method is used. For this, a special coupling is used, since the diameters of the capillary and the compressor discharge tube do not match. Direct soldering of a capillary into a thick compressor pipe is impossible without an adapter.
Is it possible to use a tube from a dropper instead of a capillary?
No, absolutely not. The capillary tube has a strictly calibrated internal diameter and length, calculated by engineers for a specific compressor power and evaporator volume. Replacing it with an arbitrary tube will either lead to defrosting of the products, or to freezing and breakdown of the compressor.
Even a microscopic speck of copper oxide that gets inside during soldering can clog the system. Therefore, when working with this unit, special cleanliness and the use of nitrogen during soldering are required.
Technology for correct soldering and installation
The process of connecting copper tubes requires not only the correct determination of “what goes where,” but also high-quality execution. The main tool here is a gas torch and solder. For refrigerators, refractory solder (containing silver) is used, which ensures the strength of the connection during vibrations and temperature changes. Soft tin solder used in plumbing is not suitable here due to the high pressure in the system.
Before soldering, the ends of the tubes must be cleaned to a shine, removing the oxide layer. A tube of smaller diameter is inserted inside a tube of larger diameter to a depth of 10-15 mm. The gap between the walls must be minimal (hundredths of a millimeter) for the effect of capillary drawing of the molten solder to work. If the gap is too large, the solder will not flow into the joint and the seal will be broken.
During the heating process, it is important not to overheat the copper. The torch flame should be directed towards the joint and not towards the tip of the tube. As soon as the copper heats up to a dark cherry color, a rod of solder is brought to the joint. The solder should melt from the heat of the tube, not from direct contact with the flame. This guarantees uniform distribution of the alloy along the entire perimeter.
☑️ Checklist for preparation for soldering
Particular attention should be paid to the filter-drier. It is installed strictly vertically, with the arrow pointing in the direction of freon movement. You cannot heat the filter itself when soldering - there is zeolite inside it, which when heated can lose its properties or, worse, spill into the system. The filter is changed every time the circuit is opened; it is a consumable item.
Table of correspondence of diameters and parameters
For convenience, the craftsmen have compiled the main parameters of the tubes into a table. Please note that dimensions may vary slightly depending on the compressor manufacturer (LG, Samsung, Beko) and refrigerant type (R134a, R600a). Refrigerant R600a (isobutane) requires less substance and often has a slightly modified geometry, but the “thicker-thinner” principle remains the same.
| Tube type | Purpose | Average diameter (mm) | Pressure in the system |
|---|---|---|---|
| Suction | Gas supply from the evaporator | 8.0 - 10.0 | Low (vacuum) |
| Discharge | Output of compressed gas to capacitor | 6.0 - 8.0 | High (up to 15 atm) |
| Capillary | Throttling (atomization) | 1.5 - 2.2 | High/low differential |
| Technological | Filling and vacuuming | 6.0 - 8.0 | Depends on the stage |
The table shows average values. To accurately select adapters or couplings, always measure the actual diameter with a caliper. The use of improperly sized fittings can lead to leaks that are extremely difficult to detect without special equipment.
It is also worth noting that for refrigerant R600a (isobutane), which is explosive, the requirements for tightness are even higher. Any microcrack in the solder is unacceptable. Therefore, after soldering all connections, the system must be checked with nitrogen under pressure before vacuuming.
Typical errors and safety measures
One of the most common mistakes is soldering without purging with nitrogen. When copper is heated in air, scale (copper oxide) forms inside the tube. Over time, this black powder is carried throughout the system by the flow of freon and oil, settling in the narrowest place - in the capillary or filter. The result is that the refrigerator stops freezing after a few months. Purging with nitrogen during soldering displaces oxygen and prevents oxidation.
Another error is overheating of the compressor. If soldering near the tubes for a long time, heat can transfer to the inside of the motor, melting the insulation of the windings or damaging the valves. It is recommended to wrap the tubes at the base with a damp rag or use heat-dissipating clamps to prevent heat from going deep into the housing.
⚠️ Attention: Work with refrigerants should be carried out in a well-ventilated area. Freon is heavier than air and in high concentrations can displace oxygen, causing suffocation. In addition, when the flame comes into contact with freon vapor, toxic compounds are formed.
Do not forget about the oil. A special refrigeration oil circulates in the system. If the compressor was lying on its side or upside down for a long time, oil could drain into the circuit. Before connecting such a compressor, you need to “blow” it through yourself (by turning it on briefly) to return the oil to the crankcase, otherwise water hammer can break the valves.
It is also critically important not to confuse the polarity of connecting the start relay to the compressor, although this does not directly apply to the tubes. But if you've already gotten to soldering, checking the electrical part won't hurt either. Incorrect connection of the relay will lead to the burnout of the starting winding in a matter of seconds.
FAQ: Frequently asked questions
Is it possible to replace copper tubes with aluminum ones?
Theoretically, it is possible using special copper-aluminum adapters, but professionals strongly do not recommend this. Aluminum is more difficult to solder, it is less ductile and more susceptible to corrosion at points of contact with other metals (electrochemical corrosion). It is better to use copper of the same grade as the original.
What to do if the tubes on the new compressor are shorter than necessary?
You cannot extend the tubes of the compressor itself. It is necessary to expand the mating parts of the circuit (condenser or evaporator pipes) using copper pipes of the appropriate diameter and connecting couplings. The extension must be carried out in compliance with soldering technology.
Is it necessary to change the oil in a new compressor?
No, modern compressors are supplied already filled with the required amount and type of oil. Opening the housing or trying to drain/add oil is strictly prohibited, as this will upset the balance and can lead to moisture and air getting inside.
Why does the refrigerator not freeze after replacing the compressor?
There may be several reasons: freon leakage due to poor soldering, capillary blockage with scale (if soldered without nitrogen), malfunction of the new one compressor (defect) or under/overfilling with refrigerant. Diagnostics with a pressure gauge station is required.
How to determine what kind of freon was in the refrigerator?
The type of refrigerant is usually indicated on a sticker inside the refrigeration chamber or on the compressor itself (for example, R134a, R600a, R12). The type of refrigerant also determines the type of oil: synthetic oil (POE) is used for R134a and R600a, and mineral oil is used for R12. You cannot mix them.
In conclusion, let us remind you: replacing a compressor is a complex technical process that requires not only knowledge of “which tube goes where,” but also the availability of special tools. If you are not confident in your abilities at the soldering or vacuum stage, it is better to entrust this work to professionals so as not to lose products and money on repeated repairs.