When the cooling system of your refrigerator stops coping with the task, and the shelves become warmer than necessary, craftsmen often mention the mysterious term “plastic metal”. For the average user, this sounds like a complex technical name for some rare part, but in fact everything is much simpler and more prosaic. Metal plastic is not a separate unit, but a colloquial name for combined tubes that are used in the evaporator or condenser circuits. It is these elements that are responsible for the circulation of the refrigerant, without which the generation of cold is impossible.
Why was there confusion and why does this material come up so often in conversations about repairs? The fact is that in modern refrigerator models, especially in the budget and mid-range segments, manufacturers are increasingly moving away from using pure copper. It is being replaced aluminum or bimetallic compounds, which are commonly called metal-plastic. Understanding what your heat exchanger is made of is critically important when planning repairs, since the methods of soldering and restoring seals for different metals are radically different.
In this article we will analyze in detail what is hidden behind this term, where exactly in the refrigerator design these elements are located and what problems equipment owners most often encounter. You will learn why replacing copper tubes with aluminum ones can be both economical and risky, and how to correctly diagnose freon leaks in hidden parts of the housing.
⚠️ Attention: Replacing evaporator tubes yourself requires specialized equipment (vacuum pump, pressure gauge station) and skills in working with refrigerants. Unprofessional intervention can lead to the final failure of the compressor.
What is hidden behind the term “metal-plastic” in modern technology
Strictly speaking, in the professional terminology of refrigeration engineers, the word “metal-plastic” does not exist. This is a popular name that has stuck due to the appearance and structure of the materials used in modern heat exchangerss. If earlier circuits were made exclusively from copper tubes, which were easily soldered and served for decades, now the industry dictates its own conditions. Manufacturers strive to reduce production costs by replacing expensive copper with cheaper alloys, often with anti-corrosion coating or plastic insulation.
The term “plastic metal” usually refers to one of two design options. The first is stainless steel or aluminum tubes coated with a layer of plastic or enamel to protect against corrosion. The second, more common option is to use tubes that visually resemble metal-plastic water pipes, but are designed to carry refrigerant. This is often called aluminum evaporators, which are installed directly into the wall of the refrigerator or freezer.
The main feature of such materials is their low thermal conductivity compared to copper, which is compensated by an increase in heat exchange area. However, there is also another side to the coin. Aluminum and its alloys are much less susceptible to repair. If a copper tube can be soldered with ordinary solder at home (although this is not recommended without experience), then restoring the tightness of “plastic metal” or aluminum requires argon welding or the use of special chemicals, which do not always guarantee a durable result.
Where the evaporator is located and how it is connected to the tubes
To understand, where exactly these notorious tubes are located, you need to look inside the refrigeration chamber. In models with the No Frost system, the evaporator is hidden behind a plastic panel on the back wall of the freezer compartment. This is where the main heat exchange process occurs: the refrigerant circulating inside the thin tubes boils and takes heat from the chamber, cooling the air. In refrigerators with a “crying” system, the evaporator can be built directly into the back wall of the fridge compartment or located in the form of a coil on the outer surface of the case.
The tubes, which users and craftsmen call metal-plastic, are most often part of this evaporator itself. They are thin channels through which freon moves. In modern models, these tubes can be integrated into an aluminum sheet (sheet evaporator) or made as a separate coil. If breakdown or corrosion occurs in this area, the refrigerant evaporates and the refrigerator stops freezing.
It is almost impossible to determine the location of the leak in such tubes without disassembling. However, there are indirect signs. If you see swelling on the inside back wall of the refrigerator or oily spots appearing under the refrigerator, this may indicate that the pipes hidden in the polyurethane foam have been reached. In such cases, repair often does not involve soldering, but a complete replacement of the evaporator or the installation of an external “crying” evaporator, which is mounted inside the chamber. corrosion I got to the tubes hidden in the polyurethane foam. In such cases, repairs often do not involve soldering, but a complete replacement of the evaporator or the installation of an external “crying” evaporator, which is mounted inside the chamber.
Why are the tubes hidden in the wall?
Hiding the evaporator in the wall of the housing (foamed evaporator) allows you to increase the useful volume of the chamber and improve aesthetics since there is no visible coil inside. However, this makes repairs almost impossible without violating the integrity of the case or installing external analogues.
Copper versus aluminum: what is the difference and which is better
The eternal dispute between supporters of copper and aluminum in refrigeration technology does not subside. To figure out what is best for your refrigerator, you need to consider the physical and chemical properties of these metals. Copper has excellent thermal conductivity and ductility. It bends easily without breaking, and, most importantly, it is easily soldered. Copper tubes less susceptible to electrochemical corrosion in copper-steel vapors that form in the refrigerator circuit.
Aluminum, which is often mistaken for “plastic metal” because of its silver color color and lightness, has its advantages. It is cheaper, lighter and resistant to certain types of oxidation, forming a protective film on the surface. However, this same film interferes with high-quality soldering. The connection of aluminum with copper (which is often used in the compressor) creates a galvanic couple, which, in the presence of moisture, leads to rapid corrosion and destruction of the seam. This is why aluminum circuits often fail faster than copper circuits.
Below is a comparative table of characteristics that will help you understand the difference:
| Characteristics | Copper | Aluminum ("Metal-plastic") |
|---|---|---|
| Thermal conductivity | High (395 W/m K) | Average (200-230 W/m K) |
| Maintainability | High (light soldering) | Low (requires welding or chemistry) |
| Service life | 15-20 years or more | 7-10 years (depending on conditions) |
| Cost material | High | Low |
The choice of material is often dictated by the manufacturer, and the user can influence little when purchasing. However, during repairs, the technician may suggest replacing the burnt area. If you are offered to replace an aluminum tube with a copper one, this is a good sign, but only if the connection is made professionally, through a steel adapter or high-quality welding, to avoid an electrochemical reaction.
Typical malfunctions and signs of a freon leak
Problems with heat exchanger tubes most often manifest themselves in the form of a refrigerant leak. Since freon is a gas that circulates under pressure, any violation of the tightness of the circuit leads to its gradual or instantaneous release. The most common cause of damage to “metal-plastic” or aluminum tubes is corrosion. Moisture entering the housing through microcracks or poor-quality insulation reacts with the metal, eating through it.
The second common cause is mechanical damage. This could be careless defrosting with a knife, when ice is chipped from the back wall, touching the hidden evaporator. Also, the tubes can burst due to water hammer or vibration of the compressor if the refrigerator is not installed level. In places where the tubes come out of the polyurethane foam layer, microcracks often form due to the constant expansion and contraction of the metal when the temperature changes.
- 🧊 Weak cooling: Food in the refrigerator compartment spoils, ice melts in the freezer, although the compressor works continuously.
- 🔊 Change in operating sound: The compressor hums louder than usual or turns on and off too often (clocking).
- 💧 Oil stains: Greasy stains appear under the refrigerator or on the back wall. Freon circulates along with the oil, and if gas comes out, the oil remains at the leak site.
- 🌡️ Condenser heating: The grill at the back of the refrigerator is either cold or hot only at the compressor, but not over the entire area.
Is it possible to replace the tubes yourself: step-by-step instructions
Replacing evaporator tubes is a complex technical process that is not formally recommended to be performed without a license and equipment. However, if you have the skills to use the tool and understand the risks, it is theoretically possible. First of all, it is necessary to dismantle the old evaporator. To do this, defrost the refrigerator, remove the inner lining (in No Frost models) or carefully cut off the foam layer (in models with a foamed circuit) to gain access to the tubes.
The next step is preparing a new evaporator. If you are replacing "plastic metal" (aluminum) with copper, you need to calculate the length and diameter of the tubes to match the compressor's performance. A route that is too long or short will upset the pressure balance in the system. After installing a new coil inside the chamber, its ends are brought out to connect to the system.
☑️ Algorithm for replacing the evaporator
The most crucial moment is soldering and vacuuming. Connections must be absolutely tight. After soldering, the system is connected to a vacuum pump and the air is removed for 30-60 minutes. This is necessary to remove moisture and air, which, when mixed with freon, form acid that kills the compressor. Only after creating a deep vacuum is the refrigerator filled with freon strictly according to the weights indicated on the unit nameplate.
⚠️ Attention: Information about the types of refrigerants (R134a, R600a) and types of oils is critical. Using the wrong freon or oil will cause immediate failure of the compressor. Always check the technical documentation of the specific model.
Prevention and extension of the service life of the heat exchanger
In order not to face the need for expensive repairs associated with replacing tubes, it is important to follow the operating rules. The main threat to “plastic metal” and aluminum is an aggressive external environment and mechanical stress. Check the condition of the door seals regularly. If the elastic does not fit tightly, warm, moist air constantly enters the chamber. This leads to increased formation of ice on the evaporator and, as a result, accelerated corrosion of the metal.
It is also worth paying attention to cleaning the condenser (the grille at the back of the refrigerator). Dust leads to overheating of the system, increased pressure in the tubes and increased load on the metal, which can cause depressurization in weak spots. Do not place the refrigerator close to the wall; ensure air circulation.
If you notice even a slight swelling of the back wall inside the refrigerator, do not expect complete failure of the equipment. This is a signal that the corrosion process has already begun and the tube is about to burst. A timely contact with a technician at the stage when the first signs appear can save the compressor, which, when operating without freon (in a vacuum), burns out very quickly due to lack of cooling and lubrication.
Frequently asked questions (FAQ)
Is it possible to solder a hole in the aluminum tube of a refrigerator?
Theoretically, you can use special two-component compounds (“cold welding”) or low-temperature solder for aluminum. However, in practice, such repairs are rarely durable due to vibration and temperature changes. It is safer to replace a section of the tube or the entire evaporator.
Why did the refrigerator begin to freeze worse after replacing the tubes?
This may be due to several reasons: the length of the new evaporator was incorrectly selected (too much or too little resistance), poor evacuation of the system (air remained) or an incorrect dose of freon filling. Repeated diagnostics by a technician is required.
How long does a “metal-plastic” evaporator last on average?
The service life greatly depends on the operating conditions and humidity in the room. On average, aluminum circuits last 7-10 years, while copper circuits can last 15-20 years or more. An aggressive environment (for example, a kitchen by the sea with salty air) reduces this period significantly.
How to distinguish a freon leak from a compressor breakdown?
When there is a freon leak, the compressor works constantly or turns on very often, but there is no cold, and the condenser (grid at the back) remains only partially cold or warm. If the compressor breaks down, it either does not turn on at all, or hums, but does not start, or works, but does not create pressure (checked by the master with a pressure gauge).