Faced with a breakdown of refrigeration equipment, many craftsmen and Enthusiasts are wondering about restoring the compressor's functionality. Changing the oil often becomes a key step in repair when the system has become contaminated with refrigerant breakdown products or mechanical particles. High-quality lubrication It is necessary to ensure the tightness of rubbing pairs and remove heat from moving elements.
However, replacing the fluid can lead to fatal consequences for the entire cooling system. Compressor is the heart of the refrigerator, and the wrong choice of composition can quickly damage it. In this article we will analyze in detail the chemical composition of lubricants, their compatibility with different types of freons and the exact volumes required for filling.
Before getting started, it is important to understand that simply “filling up the oil” is not enough. It is necessary to carry out a complete diagnosis, flushing of the system and evacuation. Errors at this stage often lead to repeated breakdowns after a short time. Mixing oils of different types is strictly prohibited, as this causes a chemical reaction with the formation of solid deposits.
Types of oils and their chemical composition
The basis for choosing a lubricant is always the type of used refrigerant. In the history of refrigeration, various substances were used, and each of them required its own chemical formula for lubrication. Today, the main players in the market remain mineral and synthetic oils.
Mineral oils are produced from petroleum by deep purification. They have excellent hygroscopicity, but do not dissolve well in modern freons. Their main competitor is POE (Polyolester) oils, which are synthetic esters. It is synthetics that have become the standard for environmentally friendly refrigerants.
⚠️ Attention: Synthetic oils (POE) are extremely hygroscopic. They absorb moisture from the air in a matter of minutes, which leads to the formation of acids within the system. An open canister cannot be stored for more than 20 minutes.
There is also semi-synthetics, which is a compromise between the first two options. It is cheaper than pure synthetics, but retains acceptable performance characteristics. The choice of a specific type depends on what kind of freon was initially filled into the circuit of your refrigerator.
Oil compatibility with types of refrigerants
A critically important parameter is the solubility of the oil in the refrigerant. If the oil does not dissolve in freon, it settles in the evaporator, creating a film that drastically reduces heat transfer. The refrigerator stops freezing, although the compressor is working properly.
For older models running on R-12 or R-134amineral oils were traditionally used. They do not mix well with these freons, but the special design of the oil separator allowed the system to work. However, with the advent of new environmental standards, the situation has changed.
Modern refrigerants, such as R-600a (isobutane) and R-407C, require the mandatory use of synthetic oils. Mineral oil in a system with R-600a simply will not return to the compressor crankcase, which will lead to oil starvation and jamming of the piston group.
Below is a compatibility table that will help you navigate the choice:
| Type refrigerant | Recommended oil type | Oil designation | Features |
|---|---|---|---|
| R-12, R-134a | Mineral | MO (Mineral Oil) | Low hygroscopicity, low cost |
| R-600a, R-410A | Synthetic | POE (Polyolester) | High solubility, afraid of moisture |
| R-22 (old splits) | Alkylbenzene | AB (Alkylbenzene) | Good compatibility with moisture residues |
| Universal | Semi-synthetic | PAG / MO+POE | Used during retrofit (replacing freon) |
When carrying out retrofit, that is, replacing old freon with a new one, the question often arises: is it necessary to completely remove the old mineral oil? Experts recommend doing a thorough flushing with nitrogen, since even 5% of mineral water residues can spoil the synthetic composition.
How much oil should be poured into the compressor
Determining the exact volume is an equally difficult task, than choosing the type of liquid. Unlike a car engine, where the level is checked with a dipstick, there is no dipstick in a hermetic refrigerator compressor. Underfilling will lead to overheating and rapid wear, and overflow to water hammer and valve failure.
There are several methods for determining the required amount. The most reliable is the factory marking on the compressor nameplate. However, if the sticker has worn off or the compressor has been moved, you have to use empirical methods. Usually the volume is from 150 to 400 grams, depending on the power of the unit.
The common method “by eye” or “as much as flowed out, so much was poured in” is erroneous. Some old oil always remains in the condenser and evaporator. If you simply replace the volume poured out during dismantling, the system will lack lubricant. It is necessary to take into account the oil remaining in the lines.
⚠️ Attention: When completely filling the system “from scratch” (after flushing), the volume of oil in the compressor should be approximately 20-25% of the internal volume of the crankcase, but not higher than the level of the sight glass (if there is one).
For domestic refrigerators For average power, the standard volume is about 200-250 grams. Industrial refrigeration compressors can require up to a liter or more. Always check the technical documentation of the specific model Danfoss, Secop or Atlant.
☑️ Checking the oil level
Technology for changing the oil in the compressor
The replacement process requires a strict sequence of actions. First, you need to bleed off any remaining refrigerant in a well-ventilated area. Then the compressor is sealed off and the waste liquid is drained. It is important to let the system drain completely for 15-20 minutes.
The next step is flushing. To do this, a special solvent or the same type of freon in liquid form is used, which is forced through the system under nitrogen pressure. This allows you to remove varnish deposits and oxidation products that inevitably accumulate at the bottom of the crankcase.
Filling of new oil is done through the process pipe. It is best to use the vacuum method: a vacuum is created in the compressor, and under the influence of atmospheric pressure the oil is sucked in through a funnel. This prevents the entry of air bubbles.
After filling, it is necessary to evacuate the system for 30-40 minutes. This will remove moisture and air. Only after reaching a deep vacuum (-1 bar) can the pipe be sealed and refilled with refrigerant.
What to do if the oil turns black?
Blackening of the oil indicates a breakdown of the insulation of the motor windings or overheating. If the oil has a burning smell or is black in color, a simple replacement will not help - a rewind or replacement of the compressor is required, since the system is contaminated with varnish combustion products.
Typical maintenance errors
One of the most common mistakes is ignoring the filter-drier. When changing oil or freon filter drier it must be changed. The old sorbent is already saturated with moisture and will not be able to protect the system from a new portion of oil, especially if it is synthetic.
Another mistake is using oil with the wrong viscosity. The viscosity is adjusted to the operating temperature of the evaporator. Freezers require more fluid oils than those for positive temperature conditions. Using thick oil in the freezer will cause it to not return to the compressor.
Some masters try to “improve” the properties of the oil by adding various additives. This is strictly forbidden. The chemistry of the refrigeration cycle has been fine-tuned for decades, and any foreign additives can cause an unpredictable reaction with seal materials or the refrigerant itself.
Diagnostics of the condition of the oil
You can assess the condition of the oil not only by color, but also by smell and the presence of suspension. If metal particles are visible in the liquid (check with a magnet or filter), this indicates serious wear of the rubbing pairs. In this case, repairs may not be economically feasible.
Oil acidity is the hidden enemy of the system. You can check it with litmus paper. If the environment is acidic, it means that the oil has reacted with moisture in the system. This requires thorough washing and installation of an additional acid filter on the suction line.
Regular monitoring of the lubricant condition helps prevent costly repairs. If you notice that the refrigerator starts to operate louder or does not turn off longer, check the oil level and quality. Perhaps it was its degradation that caused the loss of efficiency.
⚠️ Attention: If the oil has a milky tint when drained, this is a sign of water entering the system. Long-term drying with nitrogen and replacement of all rubber seals that could swell are required.
Frequently asked questions (FAQ)
Is it possible to mix mineral and synthetic oil in extreme cases?
No, you cannot mix them. Mineral and synthetic bases are chemically incompatible. When mixing, a precipitate may form, coke the capillary tube and disrupt the operation of the oil separator. Only complete flushing of the system allows you to switch from one type to another.
How often do you need to change the oil in a household refrigerator?
In a working household refrigerator, the oil is designed for its entire service life (10-15 years) and does not require scheduled replacement. It is changed only during repairs, when the system has been opened, a breakdown of the compressor has occurred, or the type of refrigerant needs to be replaced.
What are the dangers of using motor oil instead of refrigeration?
When motor oil boils (and in the compressor it partially boils) it forms carbon deposits that clog the thinnest channels of the capillary tube. In addition, it does not have the necessary cold resistance and will freeze in the evaporator, stopping the circulation of freon.
Where can I get information about the exact volume of oil for my compressor?
The exact volume is indicated in the service documentation of the refrigerator manufacturer or on the nameplate of the compressor itself (often indicated as "Oil charge" or simply the volume in grams). If there is no data, they are guided by similar models of the same power.