Repair of refrigeration equipment often begins with diagnostics of the compressor, which is the heart of the entire system. When a motor-compressor fails or begins to work intermittently, one of the first reasons technicians consider is problems with lubrication. Insufficient amount of oil or its complete absence leads to rapid overheating of the rubbing parts, jamming of the piston group and, as a result, to an expensive breakdown. However, excess lubricant can be fatal for the system, causing water hammer or blockage of the capillary tube.
The question of exactly how much fluid needs to be filled does not have a universal answer “for all at once,” since each unit has its own design features. The volume of the compressor crankcase depends on the manufacturer, series and even year of manufacture of the device. Trying to fill the oil “by eye” or according to the principle “the more, the better” is a gross mistake that can finally finish off a working mechanism. In this article we will look at the technical nuances, methods for determining the level and types of lubricants.
Before you begin any manipulations, it is important to understand that the refrigerator system is sealed and under pressure. Any intervention requires not only technical knowledge, but also compliance with safety measures. The standard oil volume in most household compressors varies from 200 to 350 milliliters, but the exact figure can only be found out from technical documentation or by weighing. The following sections will help you understand the intricacies of the replacement and topping up process.
⚠️ Attention: Before starting any work on servicing the compressor, be sure to disconnect the refrigerator from the electrical network. Residual stress or accidental starting of the engine during disassembly can cause serious injury.
Types of oils and their compatibility with refrigerants
Selecting the correct lubricant is the foundation of a successful repair. Modern and old refrigerators use fundamentally different types of oils that cannot be mixed with each other. The main separation occurs based on the type of refrigerant circulating in the system. For older models running on Freon R12mineral oils were traditionally used. They have good lubricity, but are poorly soluble in new types of refrigerants.
Modern environmentally friendly refrigerators using freons R134a, R407C or R600arequire the use of synthetic oils. Most often these are polyester (POE) or polyvinyl ether (PVE) fluids. Their chemical structure provides excellent miscibility with the refrigerant, which is necessary to return the oil from the circuit back to the compressor. If you pour mineral oil into a system with synthetic freon, it will simply settle in the heat exchangers and will not return to the crankcase, leaving the compressor without lubrication.
There is also the concept of hygroscopicity, which is critically important to consider during operation. Synthetic oils, especially polyester oils, have a high ability to absorb moisture from the air. Moisture ingress into the system leads to the formation of acids that corrode the motor windings and cause corrosion of metal parts from the inside. Therefore, such oils are supplied in sealed containers and require the fastest possible work when replacing.
- 🛢️ Mineral Oil - used in old systems with R12, not hygroscopic, but incompatible with new freons.
- 💧 Polyester oils (POE) - standard for R134a and R407C, require caution during storage due to fear of moisture.
- ❄️ Polyvinyl ether oils (PVE) - often used with isobutane (R600a), are moderately hygroscopic.
⚠️ Attention: Never mix mineral and synthetic oil in the same compressor. This will lead to the formation of a paraffin-like sediment, which will instantly clog the capillary tube and filter drier.
How to determine the required volume of oil
Determining the exact amount of liquid is a task that requires care. Manufacturers rarely indicate the oil volume in liters on the compressor nameplate; more often the type of refrigerant and electrical parameters are indicated there. However, there are proven methods for figuring out how much to pour. The first and most reliable way is to study the technical documentation for a specific model of refrigerator or compressor. Product data sheets often contain a table of filling volumes.
If the documentation is lost, which happens in most cases, you can use the weighing method. This method is considered the “gold standard” in service centers. The essence of the method is that all the oil is drained from a working compressor of the same model (or a similar series), and it is weighed on precise electronic scales. The resulting weight will be the reference for your replacement. Typically, the weight of the oil is from 180 to 300 grams, depending on the engine power.
Another method is visual, but it requires experience and accuracy. The oil level should be approximately in the middle of the height of the compressor or slightly lower when looking through the open hole (pipe). However, relying only on visual inspection is risky, since the internal design of crankcases from different manufacturers (for example Secop, Danfoss, Atlant) may differ. In some models the level may be higher, in others lower.
Therefore, when completely replacing the oil in the compressor, its volume may be slightly less than the full factory volume, since some of the old lubricant will remain in the circuit. But when replacing the compressor itself with a new one, the empty crankcase must be filled with the full volume specified in the specification.
Table of correspondence of models and volumes
For the convenience of craftsmen and enthusiasts, below is a summary table showing approximate oil volumes for popular types of compressors. Please note that the data may vary slightly depending on the specific modification and year of production. Always double-check the information on the markings on the device body.
| Manufacturer / Series | Refrigerant type | Oil type | Approximate volume (ml) |
|---|---|---|---|
| Secop (Danfoss) SC/DC | R134a | Synthetic (POE) | 250 - 300 |
| Atlant | R134a / R600a | Synthetic / Mineral | 220 - 280 |
| Embraco | R600a | Synthetic (PVE) | 200 - 240 |
| LG / Samsung (old) | R12 | Mineral | 280 - 340 |
Using a table allows you to quickly navigate, but does not provide a 100% guarantee. For example, compressors of the same series, but produced in different years, may have a modified crankcase design. Therefore, if you are doing repairs professionally, having a measuring cup and scales is a must. For household repairs, if there are no scales, you can use a syringe for refilling, measuring the volume according to the marks, but with an error of +/- 10-15%.
Why may the volumes in the table differ?
The variation in volumes is due to design changes. Engineers can reduce crankcase volume to save materials or increase it to improve cooling. The volume also depends on whether the compressor is low-speed (for quiet refrigerators) or high-speed (for fast freezing).
Step-by-step instructions for changing the oil
The process of changing the oil requires preparation of the workplace and the availability of tools. You will need: new oil of the correct type, a syringe or funnel with a thin spout, a waste container, rags and, preferably, a vacuum pump for subsequent pumping of the system. Before starting work, make sure that the refrigerator is unplugged and defrosted.
The first step is to dismantle the compressor or provide access to its pipes. If the compressor is completely removed, it must be turned upside down over a waste container. At the bottom of the housing there is a suction pipe (usually there are three, but the waste is drained through the one that leads directly into the crankcase, often this is a sealed tube or a special hole). Draining the old oil may take from 15 to 30 minutes, since the liquid is thick and viscous.
After draining, it is recommended “flush” the crankcase. To do this, you can use a small amount of the same type of fresh oil or a special flushing composition (if the situation allows). Pour in 50 ml of flushing agent, rotate the compressor shaft by hand (if it is not jammed), and drain the liquid. This will help remove wear and varnish deposits. However, at home, they often limit themselves to simply thoroughly draining the waste.
☑️ Checklist for preparing for replacement
Filling of new oil is done through the same pipe through which the waste was drained, or through a process pipe with shut-off valves. Use a syringe with a flexible tube to carefully inject the liquid inside without spilling it Control the level visually or by weight. After filling, it is necessary to immediately preserve the compressor or solder it into the system to minimize contact of oil with air.
Common mistakes when servicing the compressor
One of the most common mistakes is using the wrong oil. Self-taught craftsmen often fill motor car oil or transmission fluid, believing that “oil is oil.” This is strictly prohibited. Such oils contain additives that, when used in the refrigerator system, react with the copper of the tubes and the refrigerant, forming acid and hard deposits. The result is failure of the compressor after a few weeks or months.
Another mistake is ignoring cleanliness. Getting dust, lint from rags or metal shavings into the crankcase is fatal for bearings and cylinders. All tools and containers must be perfectly clean. Also, you should not leave the compressor open for a long time, especially in wet weather, since synthetic oils instantly absorb moisture from the air.
⚠️ Attention: Do not try to start the compressor “for testing” without oil or with open pipes. Working without lubrication, even for a few seconds, can cause irreversible scuffing on the cylinder bore.
Another mistake is overfilling. If you add more oil than normal, the excess will enter the condenser and evaporator. Oil has less heat transfer than refrigerant, and its presence in heat exchangers dramatically reduces the efficiency of the refrigerator. In addition, liquid oil can enter the compressor cylinder, causing a water hammer that will break the valves or connecting rod.
Diagnostics of the oil level without opening
Often users ask how to check the oil level without disassembling the unit. Unfortunately, in household refrigerators there is no inspection window or a probe, like in a car. The only indirect sign of oil problems is the nature of the compressor operation and the condition of the system. If the compressor operates with overheating (the housing heats up to 90-100 degrees or more), makes a metallic knock or hum, this may indicate oil starvation.
However, these same symptoms may indicate broken valves, electrical problems or a freon leak. It is impossible to make an accurate diagnosis without an autopsy. If the refrigerator has stopped freezing, and the compressor hums and turns off through the thermal relay, the likelihood of a lack of oil is high, especially if the device has been operating with a freon leak for a long time (the freon carried the oil with it).
In some cases, when the system is depressurized (for example, when the evaporator tube is broken), you may notice oily spots around the leak site. Freon in the system is under pressure and circulates together with oil in the form of an emulsion. If a leak occurs, then part of the lubricant leaves the system along with the gas. In such situations, before filling with freon, it is often necessary to add oil.
Consequences of incorrect refueling
Ignoring refueling standards leads to serious consequences. If there is a lack of oil, the rubbing parts (piston, cylinder, crankshaft) begin to run dry. The temperature rises sharply, the metal expands, and jamming occurs. The compressor hums, but does not start, consuming maximum current, which often leads to combustion of the electric motor windings.
If there is excess oil, heat transfer is disrupted. Oil entering the system creates a film on the walls of the tubes, which acts as a heat insulator. The refrigerator runs continuously, trying to gain temperature, which increases energy consumption and wear on the compressor. In the worst case, the capillary tube becomes clogged with an oil plug, and the circulation of the refrigerant is completely stopped.
It is also worth mentioning the chemical reaction. Incorrectly selected oil may react with the material of the seals (rubber bands), causing them to swell or break. This leads to internal leaks and the need to completely replace expensive system components.
Is it possible to use oil from another compressor manufacturer?
You can use oil from another manufacturer, but only with strict adherence to the chemical composition (mineral/synthetic) and viscosity. The brand (Secop, Embraco, Danfoss) is less important than the type of base. However, manufacturers often recommend their brands of oils to ensure compatibility with the materials of a particular compressor.
How often should you change the oil in a refrigerator compressor?
In a working, sealed refrigerator, the oil never needs to be changed. It is designed for the entire service life of the unit (10-15 years or more). Replacement is made only during repairs, when the system has been opened, a compressor fire has occurred, or a leak has been discovered that has carried away the lubricant.
What to do if there is old oil left in the system?
When replacing the compressor, some of the old oil always remains in the condenser and evaporator. This is fine. The main thing is not to mix different types of oils (mineral with synthetic). If the types match, the remaining old oil is not a problem. If the types are different, the system must be flushed with nitrogen or a special solvent.
Why does the oil darken after the compressor operates?
Oil darkening is a natural process. It is saturated with metal wear products, varnish deposits from overheating and burnt microparticles. Black, thick oil with a burning smell indicates that the compressor was overheating or air (oxygen) was getting into the system.