Many owners of household appliances are faced with a mysterious term when looking for information about refilling or repairing the cooling system. The phrase “liquid M for the refrigerator” often comes up in search queries, but does not always bring clarity. In fact, this is not some kind of mystical substance, but a designation of refrigerant or oil used in specific models of units, often Soviet or post-Soviet production.
Understanding what exactly is hidden under this marking is critical for proper operation and repair. Refrigerant is the “blood” of the refrigerator, circulating through the system and carrying warm. An error in choosing a substance can lead to a breakdown of the compressor or even an explosion of the system, so you need to understand the types of freon and oils with special care.
In this article we will analyze in detail the chemical composition, physical properties and rules for handling the working fluids of refrigeration units. You will learn why different types of oils cannot be mixed and how labeling affects the choice of repair strategy.
Chemical composition and physical nature of the substance
Under the general name “liquid M”, completely different chemical compounds can be hidden in everyday use. Most often we are talking about freon (freons) - hydrocarbons containing fluorine, chlorine or bromine. Older models of refrigerators, such as the famous ZIL or Biryusa, often used R-12 freon. This substance is highly stable and has excellent refrigeration properties, but it destroys the ozone layer of the planet.
Modern analogues, which may be designated by similar codes or require specific oils, operate on the basis of R-134a or R-600a. Isobutane (R-600a), for example, is explosive gas, but has high energy efficiency. It becomes a liquid in a static state only under high pressure inside the system.
⚠️ Attention: Never try to determine the type of freon by eye or smell. Some gases are colorless and odorless, but can be toxic or asphyxiating in high concentrations.
The second component that is often searched for under the name "liquid" is refrigeration oil. It is necessary to lubricate the rubbing parts of the compressor. The oil must be compatible with the type of freon. For R-12, mineral oils were used, and for new freons, synthetic polyester (POE) or polyvinyl ether (PVE) oils are required. Mixing mineral and synthetic oil is unacceptable, as this leads to the formation of a dense sediment that clogs the capillary tube.
Why should oil not be mixed with freon?
In an ideal system, oil circulates along with freon, but does not completely dissolve in it. It must return to the compressor. If chemical compatibility is impaired, the oil may precipitate or, conversely, dilute the freon too much, depriving the rubbing parts of lubrication, which will lead to jamming of the piston group.
Differences between refrigerants of different generations
The evolution of refrigerants has followed the path of increasing safety and environmental friendliness. The first generations of substances were toxic (ammonia, sulfur dioxide), then came the era of freons, which were considered safe for humans, but harmful to the environment. Now priority is given to natural refrigerants and mixtures with low global warming potential.
The key difference lies in the operating pressure and boiling point. R-12 boils at a temperature of -29.8 ° C, which was ideal for old-style household freezers. More modern R-134a boils at -26.3°C, which requires more efficient compressors or a larger heat exchanger surface to achieve the same temperatures in the freezer.
Below is a comparative table of the main characteristics of refrigerants that could be designated as “liquid M” in different contexts:
| Refrigerant type | Chemical formula | Boiling point (°C) | Type of compatible oil |
|---|---|---|---|
| R-12 (Freon-12) | CCl2F2 | -29.8 | Mineral (MO) |
| R-134a | CH2FCF3 | -26.3 | Polyester (POE) |
| R-600a (Isobutane) | C4H10 | -11.5 | Mineral / Alkylbenzene |
| R-407C | Blend | -43.5 ( glide ) | Polyester (POE) |
Replacing one type of refrigerant with another (retrofit) is a complex procedure. It requires not only evacuation of the system, but also complete flushing of the circuit from old oil, replacement of the filter-drier and often - replacement of the compressor itself with a model adapted for the new gas. An attempt to fill R-134a into a system designed for R-12 without changing the oil and filter will lead to rapid failure of the compressor.
The role of oil in the cooling system
When they talk about “liquid M” in the context of maintenance, they often mean oil. Unlike freon, which is in a closed circuit and ideally should not leave the system, oil requires periodic checking and replacement only during repairs. Its main function is to reduce friction between the piston and cylinder of the compressor.
However, oil also has a second, no less important function: it helps remove heat from heating engine parts. In addition, the oil is carried by the freon flow through the system and must have a certain viscosity in order to return back to the compressor crankcase. If the viscosity is too high, the oil will stagnate in the evaporator, reducing cooling efficiency. If it is too low, the pressure in the lubrication system drops.
Modern synthetic oils are highly hygroscopic, that is, they actively absorb moisture from the air. Hydrolysis Synthetic oil, when in contact with water, leads to the formation of acids that corrode the electric motor windings and metal parts. Therefore, an opened canister of synthetic oil is stored for a very short time.
- 🛢️ Mineral oils are cheap, time-tested, but do not work with new environmentally friendly freons.
- 💧 Synthetic (POE/PVE) - have excellent lubricating ability, but require absolute dryness of the system.
- 🔄 Alkylbenzene (AB) - an intermediate option, often used as a transition oil for retrofitting systems.
⚠️ Attention: Store an open canister with synthetic oil for no more than 2-3 days, tightly closing the lid. Moisture absorbed from the air will make the oil unsuitable for use in the refrigerator.
Diagnostics of a lack of working fluid
How to understand that there is not enough “liquid M” in the refrigerator, that is, refrigerant? The cooling system is sealed, and freon is not consumed during operation, like gasoline in a car. If the level drops, there is a leak. It is difficult to independently determine the location of the leak without equipment, but indirect signs are obvious.
The first sign is that the refrigerator runs constantly without turning off. The compressor hums continuously, trying to gain temperature, but the sensor does not give the command to stop. The second sign is weak cooling or its complete absence. In this case, the condenser (grid at the back) may be barely warm or cold, although the compressor is hot.
Sometimes a leak is accompanied by the appearance of oil stains under the refrigerator or on the floor where the unit is installed. The freon evaporates, but the oil that circulated with it remains. A characteristic chemical smell may also appear if the leak occurred inside the cabinet and the gas escapes through the seals.
It is important to distinguish between a lack of freon and a malfunction of the thermostat. If the compressor does not turn on at all or turns on rarely, and there is heat in the chamber, the problem is most likely in the electrics or sensors, and not in a “liquid” leak.
Safety precautions when working with refrigerants
Working with refrigerants falls into the category of high-risk work. Even if you are not a professional craftsman, knowledge of safety rules is necessary. Firstly, many freons are heavier than air. If there is a large leak in an unventilated room, they displace oxygen, which can lead to suffocation.
Secondly, upon contact with an open flame (gas stove, cigarette), some freons disintegrate to form phosgene a chemical warfare agent. Therefore, smoking or lighting a fire near the repair site where gas may escape is strictly prohibited.
Thirdly, liquid freon, escaping from the cylinder, has an extremely low temperature and can cause instant frostbite of the skin and mucous membranes of the eyes. Contact of a jet of gas in the eyes can lead to blindness.
- 🥽 Always use safety glasses and gloves when working with refrigerants.
- 🌬️ Ensure strong ventilation of the room during work.
- 🔥 Eliminate any sources of open flame and sparks in radius of 3-5 meters.
☑️ Safety rules when refueling
The process of refueling and restoring the system
Restoring the amount of “liquid M” in the refrigerator is not easy "topping up". This is a complex technological process. First, the technician must find and repair the leak. The system is then evacuated. This is a critical step: you need to remove air and, most importantly, water vapor from the circuit. Boiling water at low pressure allows you to pull moisture out of hard-to-reach places.
After vacuuming, filling is done. The amount of refrigerant is dosed to the nearest gram. Modern instructions for models Indesit, Atlant or LG on the nameplate (usually inside the chamber or on the back) always indicate the exact amount and type of freon. Overdosing is just as dangerous as underfilling: it leads to an increase in pressure, load on the compressor and possible rupture of the tubes.
The process ends by checking the operation of the unit under load. The wizard checks the compressor consumption currents, the temperature in different parts of the circuit and the time it takes to reach the operating mode. Only after this is the filling fitting sealed.
⚠️ Attention: Technical characteristics and requirements for oils may vary depending on the specific modification of the compressor. Always check the data on the nameplate of your device with the current compatibility tables of manufacturers.
Independent refilling without a vacuum pump and scales ("by eye" or by pressure) in 90% of cases leads to incorrect operation of the refrigerator and rapid re-breakdown. The pressure in the system depends on the ambient temperature, so relying only on the readings of the pressure gauge without taking into account other parameters is a gross mistake.
Is it possible to refuel the refrigerator yourself?
Theoretically, it is possible if you have the skills to solder copper pipes, a vacuum pump, a pressure gauge station and scales. However, if you are not experienced, the risk of damaging the compressor or creating an explosive situation (with R-600a) is extremely high. Saving on calling a technician often results in the purchase of a new refrigerator.
Frequently asked questions (FAQ)
Is it possible to mix freon R-12 and R-134a?
Absolutely not. These substances have different chemical structures and require different types of oils. Mixing will result in the formation of acids, deterioration of the engine insulation and plugging of the system. When switching to another type of freon, a complete flushing of the system and an oil change are required.
How often do you need to change the “liquid” (freon) in the refrigerator?
Freon is a working fluid in a closed cycle and is not consumed. It needs to be changed or added only in case of leakage caused by mechanical damage or corrosion of the tubes. In a working refrigerator, freon lasts for decades without replacement.
What is dangerous about mineral oil in a system with R-134a?
Mineral oil does not dissolve well in R-134a freon and does not return to the compressor. It settles in the evaporator, creating an oil film that interferes with heat transfer (the refrigerator stops freezing), and the compressor remains without lubrication and burns out.
Where can I find information about the type of liquid for my refrigerator?
The exact information is indicated on the factory sticker (nameplate), which is usually located inside the refrigerator compartment on side wall, on the door or on the rear wall of the cabinet. It shows the type of refrigerant (for example, R600a) and its mass in grams.