A situation when the refrigerator stops freezing or makes unusually loud sounds often confronts the owner with a difficult choice: call a technician or try to figure it out on his own. One of the critical components that require attention during diagnosis is compressornamely its lubrication system. If you notice that the unit is overheating and the noise level has increased significantly, it may be time to check the amount and condition of the lubricant. A lack of oil or its complete drying out can lead to jamming of the piston group in a matter of hours of operation.
However, the procedure for adding or replacing oil in a sealed circuit of a refrigeration unit is not just “open and pour”. This is a complex technical process that requires an understanding of the operating principles of the freon circuit and compliance with strict safety rules. It is important to note right away: in a working, sealed refrigerator, oil is not consumed and does not require scheduled replacement throughout its entire service life, which can reach 10-15 years. The need for intervention arises only after repair, replacement of the compressor, or when a refrigerant leak is detected when the system has been depressurized.
Before taking up tools, you must clearly understand the risks. Independent intervention in the refrigerant circulation system without the appropriate equipment (vacuum pump, pressure gauge station) can lead to permanent failure of the equipment. If you are not confident in your abilities, it is better to entrust this work to professionals. But if the decision is made, and you have the necessary soldering and vacuum skills, this article will become your detailed guide to choosing the right product and the technology for its implementation in refrigeration unit.
⚠️ Attention: Compressor maintenance work requires complete discharge of the refrigerant from the system. The release of freon into the atmosphere is prohibited by environmental standards, and the entry of air and moisture into the circuit if assembled incorrectly is guaranteed to disable the refrigerator.
Signs of lack of lubrication and diagnostics of the compressor
You can understand that the compressor does not have enough oil or it has lost its properties by a number of indirect signs that appear in the operation of the refrigerator. The first and most obvious symptom is a change in background sound. A serviceable motor hums smoothly and monotonously, while with a lack of lubrication, metallic knocks, grinding noises or a sharp howl appear. This indicates that the rubbing parts are running “dry”, which inevitably leads to their rapid wear and heating.
The second important indicator is the temperature of the compressor housing. During normal operation it is warm, but not scalding. If the body is heated to such an extent that it is impossible to touch it, this is a direct signal of a violation of heat transfer and lubrication. Often in such cases, the thermal protection relay is triggered, and the refrigerator begins to work cyclically: it turns on for a couple of minutes, gets very hot and turns off. This mode of operation kills the motor windings and the mechanical part.
For accurate diagnosis, it is necessary to analyze a combination of factors. Noise does not always mean a lack of oil; sometimes the cause is vibration of the housing or a malfunction of the start relay. However, if you are planning to replace the compressor or have already repaired the circuit, the question of the quantity and type of oil automatically arises. New compressors are already filled with oil, but its volume may be insufficient for long pipelines or large-area evaporators, so topping up is often required topping up.
Selecting the type of oil for the refrigeration compressor
A critically important step is the correct choice of lubricant. Using the wrong oil will lead to a chemical reaction with the refrigerant, the formation of acids, varnish deposits and, as a result, blockage of the capillary tube and failure of the compressor. Modern refrigerators use three main types of oils, and mixing them is strictly prohibited without first flushing the system.
The first type is mineral oils. They are used in older models of refrigerators running on R-12 freon, as well as in some modern units using hydrocarbon refrigerants (R-600a). These oils have good lubricity, but are poorly soluble in synthetic refrigerants. The second type is polyester (POE) oils. This is the standard for modern environmentally friendly freons R-134a and R-407c. They are hygroscopic, that is, they actively absorb moisture from the air, which requires special care when working.
The third type is polyvinyl ether (PVE) oils, which are often used in air conditioners and some industrial systems, but are less common in household refrigerators. The main rule is that the type of oil must match the type of refrigerant and the requirements of the compressor manufacturer. If you are replacing a compressor that already has oil in it, be careful not to mix it with any remaining product in the lines if the types are different.
| Oil type | Compatible refrigerant | Features | Hygroscopicity |
|---|---|---|---|
| Mineral | R-12, R-600a | Cheap, time-tested | Low |
| Polyester (POE) | R-134a, R-407c, R-410a | High stability, aggressiveness to insulation | High |
| Alkylbenzene (AB) | R-22, R-12, R-134a | Intermediate option, good compatibility | Medium |
| Polyvinyl ether (PVE) | R-410a, R-32 | High lubricity | Medium |
Preparation for the replacement or topping up procedure
The process of filling a compressor with oil requires careful preparation of the workplace and tools. You will need not only the oil itself, but also specialized equipment. First of all, a vacuum pump is needed to remove air and moisture from the system. The presence of moisture in the circuit with polyester oil is unacceptable, as this leads to the formation of acid, which corrodes the motor windings from the inside.
You will also need a torch (gas or oxy-acetylene) for soldering copper tubes, solder with flux, wire cutters, pliers and a syringe or measuring cylinder to accurately measure the volume of oil. The volume of liquid poured is strictly regulated by the compressor manufacturer and usually ranges from 200 to 400 grams, depending on the model. Overfilling the oil is just as dangerous as underfilling it: excess liquid in the system impairs heat transfer and can cause water hammer.
Before starting work, the refrigerator must be disconnected from the network for at least several hours so that the pressure in the system is equalized and the oil flows into the crankcase. The work area should be well ventilated, as freon vapors and combustion products during soldering can be harmful. If you are working with polyester oils, ensure that the oil container is opened immediately before filling to minimize exposure to air.
⚠️ Caution: Never leave the polyester oil container open for more than 10-15 minutes. It absorbs moisture from the air instantly, which can ruin the entire work.
Technology for filling oil through a capillary tube
There are several methods for filling oil, but the most common and effective in repair conditions is the method of vacuuming through a capillary tube. This method allows you not only to fill the required volume, but also to ensure that there are no leaks or moisture in the system. First, you need to dismantle the old compressor (if replacing) or cut off the service tube on a running unit (if topping up without replacement is required, which is done rarely and only through special valves).
The process begins with creating a vacuum. After installing a new compressor or preparing an old one, a hose from the vacuum pump is connected to its suction pipe. In parallel to the same pipe, a container with oil is connected through a tee or adapter. The pump turns on and a deep vacuum is created in the system. Under the influence of vacuum, the oil from the container begins to be sucked into the compressor.
You need to control the amount of oil poured using scales or marks on the graduated cylinder. As soon as the required volume enters the compressor (for example, 280 ml), the supply is shut off. Then the compressor should be “driven” for several seconds in a vacuum so that the oil disperses through the internal cavities, after which the suction tube is sealed. It is important not to turn on the compressor without load (vacuum) for more than 30-60 seconds, so as not to overheat it.
☑️ Checklist for preparing for refueling
Bleeding the system and removing air
After the oil is filled and the compressor is in place, the stage of assembling the circuit and removing air begins. The air remaining in the system contains nitrogen and oxygen, which at high pressures and temperatures can react with the oil, forming oxides. In addition, the air creates an “air lock”, which interferes with the circulation of the refrigerant and increases the condensation pressure, which leads to overload of the compressor.
Evacuation is a mandatory procedure. A pressure manifold and a vacuum pump are connected to the service pipe. The pump is turned on for 15-30 minutes (the time depends on the power of the pump and the volume of the system). The vacuum gauge should show a value close to -1 bar (or 760 mm Hg. Art.). If the pressure gauge needle begins to creep up after turning off the pump and closing the valves, it means that there is a leak in the system that must be found and eliminated before refilling with freon.
Only after successful evacuation is the refrigerant charged. Oil and freon must work together. If you have replaced the compressor, it is also recommended to replace the filter drier, since the old one could have absorbed moisture and oil breakdown products. The filter is installed immediately after evacuation, before soldering the capacitor, and soldering must be done quickly so that the filter does not have time to pick up moisture from the air.
What will happen if you do not make a vacuum?
The air remaining in the system will lead to an increase in operating pressure, overheating of the compressor and oxidation of the oil. In a system with R-134a and POE oil, this is guaranteed to cause the formation of acid deposits on the windings, which will lead to a short circuit and combustion of the motor after several months of operation.
Frequent errors and precautions
When repairing refrigerators on their own, beginners often make mistakes that nullify all their efforts. One of the most common is using oil with the wrong viscosity. Viscosity is selected depending on the boiling point of the refrigerant and the design of the compressor. Oil that is too thick will not have time to return from the evaporator to the compressor, causing oil starvation, and oil that is too thin will not create the desired film on the rubbing parts.
Another mistake is neglecting cleanliness. Even a microscopic speck of dust or shavings entering the circuit can clog a capillary tube with a diameter of less than a millimeter. All tools must be clean, and the ends of the tubes should be capped before soldering. It is also dangerous to use an open flame near the plastic elements of the refrigerator or without protecting the back wall.
Do not forget about safety precautions when working with freon. Although modern freons are not toxic in small doses, in high concentrations they displace oxygen. In addition, when heated with an open flame, freon can decompose to form phosgene, a chemical warfare agent. Therefore, you need to solder the tubes quickly and in a ventilated area.
⚠️ Attention: The characteristics of refrigerants and requirements for oils may change depending on new environmental standards. Always check the information on the label of a particular compressor, as the manufacturer may change the specifications for the same model in different years of production.
FAQ: Frequently Asked Questions
Is it possible to mix mineral and synthetic oil in the compressor?
Strongly not recommended. Mixing different types of oils (for example, mineral and polyester) can lead to separation of the mixture, sedimentation and loss of lubricating properties. If you need to switch from one type to another, the system must be thoroughly washed with a special solution or nitrogen.
How often should you change the oil in the refrigerator?
In the factory, the oil is filled for the entire service life of the refrigerator and does not require replacement. It only needs to be changed or topped up when repairing the compressor, replacing the motor, or when a serious leak is detected when the system has been open to air for a long time.
Which oil is best to use for R-600a?
For R-600a refrigerant (isobutane), mineral oil is most often used, since it dissolves well in this hydrocarbon refrigerant. However, some manufacturers may also use synthetic analogues, so always check the markings on the compressor.
What to do if moisture gets into the system?
If there is a suspicion of moisture ingress, it is necessary to replace the filter drier with a new one and repeat the vacuum procedure for a longer time (up to 1 hour). In critical cases, the system is flushed with nitrogen.
Is it possible to fill in more oil than normal?
No, overfilling oil is dangerous. Excess oil will get into the heat exchangers (condenser and evaporator), cover their walls with a film, which will sharply worsen heat transfer. The refrigerator will stop freezing, and the compressor will work overload. In addition, liquid oil can get into the compressor cylinder and cause water hammer, breaking the valves.