When household the refrigerator stops coping with its main task - freezing food, and the compressor begins to hum or turns off after a few seconds of operation, the owner is faced with the question of diagnostics. Often the cause of a breakdown is a violation of the circulation of the refrigerant or wear of the rubbing parts of the motor-compressor. It is at this moment that many craftsmen and amateurs ask the question: what is the name of the refrigerator oil that is poured inside the system, and is it possible to top it up or replace it yourself?
Unlike a car engine, where changing engine oil is a regular procedure, refrigeration compressor is a sealed unit, designed to operate without human intervention throughout its entire service life. However, when making repairs that involve replacing a compressor or clearing blockages, knowing the type of lubricant being used becomes critical. An incorrectly selected liquid can instantly damage a new part or clog a capillary tube.
In this article we will look in detail at what types of oils exist, how they differ chemically and why they should absolutely not be mixed. You will learn how to determine what exactly is in your system, and what risks are involved in trying to save on specialized lubricants. Understanding these nuances will help you avoid costly mistakes when restoring the functionality of refrigeration equipment.
Chemical composition and main types of oils
The main function of the lubricant in the refrigerator is to reduce friction between the moving parts of the compressor and remove heat. However, unlike other mechanisms, this substance is constantly in contact with the refrigerant (freon) and is under high pressure. That is why oil for a refrigeration compressor must have a unique set of properties: low pour point, high dielectric strength and chemical stability.
Historically, the type of oil used directly depends on the type of freon for which the system is designed. For a long time, the standard was mineral oils obtained by refining petroleum. They worked well with CFC and HCFC refrigerants (for example, R12, R22). However, with the advent of environmentally friendly freons, such as R134a and R600a, a new approach was required. Mineral oil simply does not dissolve in new refrigerants, which would lead to the fact that the oil would remain in the evaporator and not return to the compressor, causing it to starve of oil.
Synthetic oils were developed to solve this problem. The most common type for household refrigerators today is polyester oil. It has excellent solubility in modern freons and provides reliable lubrication. There are also PAG (Polyalkylene Glycol) type oils, but they are more often used in car air conditioners and are extremely hygroscopic, which makes their use in household appliances risky without special equipment. POE (Polyol Ester) - polyester oil. It has excellent solubility in modern freons and provides reliable lubrication. There are also PAG (Polyalkylene Glycol) type oils, but they are more often used in car air conditioners and are extremely hygroscopic, which makes their use in household appliances risky without special equipment.
⚠️ Attention: Never try to determine the type of oil by eye color or viscosity alone. Mineral and synthetic oils may look equally clear, but their chemical incompatibility will lead to the formation of sludge and acids that will destroy the engine windings in a matter of days.
Differences in the chemical structure also dictate operating rules. If mineral oils are relatively forgiving to moisture, then synthetic ones absorb moisture from the air like a sponge. This leads to hydrolysis - the breakdown of the oil into acids and alcohols, which causes corrosion of metal parts and breakdown of the electric motor insulation. polyester oils absorb moisture from the air like a sponge. This leads to hydrolysis - the breakdown of oil into acids and alcohols, which causes corrosion of metal parts and breakdown of the insulation of the electric motor.
Mineral oils: classics for older systems
Mineral oils, often designated by an abbreviation MO (Mineral Oil), are produced from crude oil through deep refining. For decades they have been the industry standard due to their availability and good lubrication properties. Such oils were ideal for CFC-based refrigerants that dominated refrigeration technology of the last century.
The main feature of mineral oils is their poor solubility in water and low hygroscopicity. This means that they do not absorb moisture from the atmosphere as actively during short-term contact during repairs as their synthetic counterparts. However, they have a serious drawback: they do not mix with modern freons. If mineral water is poured into a system designed for R134a, it simply will not circulate along with the gas, but will settle in the heat exchangers, drastically reducing the cooling efficiency.
The viscosity of mineral oils is selected strictly for the design of the compressor. For low-power piston compressors, typical of home refrigerators, oils with a viscosity of ISO 10, 15 or 22 are usually used. More viscous grades can be used in industrial installations or rotary compressors.
If you are repairing an old Soviet refrigerator or a model from the early 2000s that runs on R12 freon, most likely it is mineral oil inside. Replacing it with a synthetic one without thoroughly flushing the system is unacceptable, since mineral water residues can react with the new oil or simply contaminate the system.
Synthetic oils: the standard of modern technology
With the advent of environmental standards and the ban on the use of freons, which destroy the ozone layer, the industry switched to new refrigerants. Along with them came synthetic oils, the main representative of which is POE (Polyol Ester). This is a complex chemical compound created in laboratory conditions, and not extracted from the bowels of the earth.
The key advantage of POE oils is their complete solubility in freons R134a, R404A, R507 and R600a. This property ensures that the oil returns to the compressor: the oil circulates along the circuit along with the gas, lubricates the parts and returns back without forming oil plugs in the evaporator. Without this property, modern compact refrigerators with thin capillary tubes simply could not work.
However, synthetics also have a downside. Hygroscopicity polyester oils are incredibly high. They are able to absorb moisture from the air hundreds of times faster than mineral oils. Moisture entering the system causes two main problems:
- ❄️ Formation of ice plugs in the capillary tube, which blocks the circulation of freon.
- 🧪 Chemical reaction of hydrolysis, leading to increased acidity of the oil and corrosion of internal parts.
- ⚡ Reduction in dielectric strength, which can lead to breakdown of the compressor windings and short circuit.
That is why when working with modern refrigerators, the time during which the system is open to the atmosphere should be minimal. Often, craftsmen use special devices to plug pipes or flush the system with nitrogen to displace moist air.
What happens if you mix mineral and synthetic oil?
Mixing different types of oils (mineral and polyester) will lead to liquid separation, flaky sediment and loss of lubricating properties. At best, the compressor will overheat, at worst, it will jam after a few minutes of operation. Sediment can also permanently clog the filter drier and capillary tube.
Compatibility table of oils and refrigerants
The correct selection of lubricant is impossible without understanding what refrigerant is used in your refrigerator. This information is usually located on a sticker located on the back or inside the camera. Below is a table to help you navigate compatibility.
| Refrigerant type | Recommended oil type | Alternative | Note |
|---|---|---|---|
| R12, R22, R502 | Mineral (MO) | Alkylbenzene (AB) | Old systems, high requirements for purity |
| R134a, R404A, R507 | Polyester (POE) | Polyvinyl ether (PVE) | High hygroscopicity, requires caution |
| R600a (Isobutane) | Mineral (MO) / POE | Alkylbenzene (AB) | Highly purified mineral water is often used |
| R410A, R32 | Polyester (POE) | - | High operating pressure, synthetic only |
It is important to note that there are also alkylbenzene oils (AB), which occupy an intermediate position. They are less hygroscopic than POE, but are better soluble in some freons than mineral ones. However, in household refrigerators they are less common, mainly in specific industrial models.
When choosing an oil to replace, always rely on the recommendations of the compressor manufacturer, and not just on the type of freon. Different manufacturers (Danfoss, Embraco, Secop, LG) may have their own preferences for viscosity and additives.
The process of changing the oil and filter-drier
Changing the oil in the refrigerator is not just a matter of “draining and filling.” This is a complex technical procedure that requires evacuation of the system. The oil in the compressor is under pressure and mixed with freon. Simply by biting off the tube, you will not be able to drain it completely, since some of the oil remains in the windings and on the walls of the crankcase.
The replacement process usually looks like this. First, all refrigerant is removed from the system (this must be done by a certified specialist with a license to work with freons). Then the compressor is cut off. The old oil is drained, and flushing fluid is often added to the system to remove decay products of the old oil and contaminants. After this, a new compressor is installed and always a new filter drier filter drier.
The filter drier is a critical element. It contains zeolite or molecular sieve, which absorbs moisture and acidic residues. Whenever the system depressurizes, the filter must be replaced, since its resource is limited. If you leave the old filter, it can quickly become saturated and stop protecting the system, or worse, begin to release accumulated moisture back.
After assembling the system, it is necessary to create a deep vacuum using a vacuum pump. This is necessary to remove air and evaporate moisture that could get inside. The evacuation time depends on the pump power and the volume of the system, but is usually at least 15-30 minutes. Only after the required residual pressure is achieved, the calculated amount of freon is charged into the system.
☑️ Checklist when changing the oil
⚠️ Attention: Technical characteristics of refrigerators, types of used Refrigerants and oil requirements may vary by model and year. Always check the technical documentation (service manual) of the specific manufacturer before starting work. The use of unsuitable materials will void the warranty.
Common errors and myths
There are many myths surrounding refrigerator repairs that can lead to fatal consequences for the equipment. One of the most common is the statement that “there is no need to change the oil in the refrigerator, it is there forever.” This is only true if the system is sealed. If the compressor burns out, the oil in the system turns into acid, which eats away the copper and insulation. Adding new oil to a dirty system means killing the new compressor.
Another myth says that you can add any transformer or spindle oil if it is “similar”. This is categorically false. Dielectric strength refrigeration oil is much higher than that of conventional industrial oils. The use of surrogates will lead to breakdowns and fire.
It is also a mistaken opinion that the amount of oil does not matter, the main thing is that the compressor does not run dry. In fact, too much oil (overfilling) is just as dangerous as underfilling. Excess oil will enter the condenser and evaporator, occupying the volume intended for freon. This will lead to an increase in condensation pressure, overheating of the compressor and lack of cold.
Some “masters” advise adding oil directly through the filling valve without opening the system. This cannot be done efficiently without special equipment for injection under pressure, and most often this procedure ends with air and moisture entering the circuit.
Frequently asked questions (FAQ)
Is it possible to use automobile motor oil for a refrigerator?
No, absolutely not. Motor oils contain additives that, when in contact with freon and copper, can precipitate or cause corrosion. In addition, they do not have the necessary dielectric strength and can cause a short circuit in the compressor windings.
How often do you need to change the oil in the refrigerator?
In normal operation, the oil in the refrigerator is never changed. It is designed for the entire service life of the unit (10-15 years). Replacement is required only during repairs: if the compressor burned out, a breakdown of the circuit occurred, or the system was open to air for a long time.
What is the difference between oil for R134a and R600a?
For R134a, synthetic polyester oils (POE) are most often used, since mineral oils do not dissolve in it. For R600a (isobutane), the use of special highly purified mineral oils or alkylbenzene oils is often allowed, since isobutane mixes well with them, but the requirements for purity and absence of moisture remain high for both types.
What happens if you confuse mineral oil with synthetic oil?
When mixed, separation and loss may occur sediment, loss of lubricating properties. If mineral water is left in a system designed for synthetics (or vice versa), the compressor may overheat, and the heat exchangers will become contaminated with an oil film, which will drastically reduce cooling capacity.
Where to buy special oil?
Refrigeration oil is a specific product. It is rarely found in regular hardware stores. Look for it in specialized refrigeration equipment stores, suppliers of spare parts for household appliances, or on industrial marketplaces. Be sure to request a certificate of conformity and check the tightness of the packaging.