Modern refrigerators with the system No Frost have become a standard in the household appliances market, eliminating the need for regular manual defrosting. This technology is based on a complex process of air circulation, which is impossible without a key element - the evaporator. It is this part that is responsible for directly cooling the interior of the chamber, taking heat from the air.
Many owners do not even think about what is happening behind the plastic panels of the rear wall until they are faced with an increase in temperature or ice. Understanding how it works and functions will help you quickly diagnose faults and avoid costly repairs. In this article we will analyze in detail the physical processes occurring inside the unit. heat exchanger, will help you quickly diagnose faults and avoid costly repairs. In this article we will analyze in detail the physical processes occurring inside the unit.
The principle of operation is based on the ability of the refrigerant to change its state of aggregation. Liquid freon, entering the evaporator tubes under low pressure, boils at very low temperatures. This process requires a huge amount of thermal energy, which it takes from the walls of the tubes, cooling them to extreme values.
Physical principles of the heat exchanger
The central element of the cooling system is the evaporator, which is a coil of thin tubes, often equipped with aluminum plates to increase the heat exchange area. When the compressor pressurizes, the refrigerant passes through the filter drier and capillary tube, where it expands sharply and enters the evaporator. Here a phase transition of a substance from a liquid to a gaseous state occurs.
The surface temperature of the evaporator tubes in the freezer can drop to -20...-30°C. A nearby fan forces air from the chamber through this cold coil. Passing between the cold plates, the air flow gives up its heat and returns to the chamber already cooled. This cycle is repeated constantly, maintaining the set temperature.
However, such a scheme has an inevitable side effect. The air always contains water vapor. Upon contact with the ice plates of the evaporator, the moisture instantly condenses and turns into frost. If it were not for the defrosting system, the ice “coat” would quickly block the air channels, and the refrigerator would stop freezing.
⚠️ Attention: Never try to scrape ice from the evaporator with sharp objects. Thin tubes of the heat exchanger will be damaged, which will lead to an immediate release of freon and expensive repairs.
Why aluminum?
Aluminum evaporator plates have high thermal conductivity, which allows you to quickly transfer cold to the air. However, they are very sensitive to acids and alkalis, so aggressive household chemicals should not be used when cleaning.
Automatic defrosting system
To compensate for ice build-up, No Frost refrigerators have an automatic defrosting algorithm. This process is controlled by an electronic module or a mechanical timer, which counts the operating time of the compressor. Typically, the defrost cycle starts every 8-12 hours of operation of the unit.
When the defrost cycle starts, the compressor and fan stop. At the same time, the Defrost heating element (tubular electric heater) located directly under the evaporator or mounted in its lower part is switched on. Thermal energy heats the plates, and the accumulated ice melts.
The resulting water flows into a special pan located under the chamber, from where it evaporates naturally due to the heat from the operating compressor. The whole process takes from 15 to 30 minutes, after which the system switches back to cooling mode.
☑️ Signs of a working defrost system
Key components of the cooling unit
The efficiency of the evaporator depends on the coordinated interaction of several sensors and heating elements. Engineers have provided several levels of protection and control so that the system operates autonomously and safely.
The main elements of the unit are:
- ❄️ Evaporator —a copper or aluminum coil where freon boils.
- 🔥 Defrost heating element —a heating element that melts ice.
- 🌡️ Defrost sensor (defrost thermostat) - opens the heating element circuit when a certain temperature is reached (usually +10°C), preventing overheating.
- 🛡️ Thermal fuse - emergency element that breaks the circuit, if the defrost sensor fails and the temperature exceeds the critical temperature (about +70...+80°C).
It is important to understand that all these elements are connected into a single electrical circuit. If the thermal fuse burns, the circuit will open and the heating element will stop turning on, even if the heater itself is working. Diagnostics often begins with checking the integrity of this circuit.
In modern models Samsung or LG the functions of the mechanical timer and thermostats are often taken over by the main electronic control module, which receives data from digital temperature sensors. This increases accuracy, but complicates diagnostics without special equipment.
Symptoms of a malfunction of the evaporator and defrost system
Understanding how the evaporator works in a No Frost refrigerator allows you to quickly identify a breakdown based on indirect signs. Most often, problems are associated with a violation of the defrost cycle, and not with a freon leak.
The first and most noticeable sign is the formation of a “fur coat” or block of ice on the back wall of the freezer or refrigerator compartment. This indicates that the ice does not have time to melt and begins to grow, blocking the channels for air circulation.
Other symptoms include:
- 📈 Increase in temperature in the chambers when the compressor is running.
- 🔊 The appearance of extraneous sounds: hum, crackling or whistling (this is a fan touches ice build-ups).
- ❄️ Uneven cooling: it is colder at the back wall than at the doors.
If you notice that the refrigerator is not freezing well, and ice is visible on the back wall, most likely the problem lies in one of the elements of the defrost system: the heating element is burnt out, the sensor is stuck or burnt out fuse.
| Malfunction | Symptom | Probable cause |
|---|---|---|
| Ice on the back wall | Weak cooling, hum | Faulty heating element or timer |
| The refrigerator does not turn on | Silence, no light | Thermal fuse has burned out |
| Constant operation of the compressor | Overconsumption of energy, ice | Sticking timer contacts |
| Water on the floor | Puddles around the unit | Clogged drainage hole |
Diagnostics and replacing system elements
To carry out diagnostics, you need to gain access to the evaporator. On most models, this requires removing the rear plastic panel in the freezer and removing the air ducts. Before starting work, the unit must be defrosted for at least 12 hours so that all hidden ice melts.
The elements are checked using a multimeter in resistance measurement mode. The normal resistance of a defrosting heating element is usually from 200 to 400 Ohms (depending on the power and model). If the device shows an open circuit (infinity) or a short circuit (zero), the heating element must be replaced.
The defrost sensor at room temperature should “ring” (have resistance), and when cooled (for example, if you blow on it with a hairdryer and then sharply cool it with a freezing spray), it should open the circuit. A thermal fuse in good condition always has zero resistance.
⚠️ Attention: Technical characteristics of the elements (resistance, response temperature) may vary depending on the brand. Always check the markings of the new part with the original before installation.
During assembly, it is important to correctly install the drainage pipe and make sure that it is not pinched. An installation error can lead to water flowing into the housing during the next defrost, causing corrosion or a short circuit.
Prevention and care of the No Frost system
Although the system is called “no frost”, it still requires minimal attention for long service. The owner's main task is to ensure proper air circulation and prevent excess moisture from getting inside the chambers.
It is recommended to periodically check the tightness of the rubber seals on the doors. If the rubber is cracked or the door does not close tightly, warm, moist air constantly enters the chamber. The evaporator cannot cope with such a volume of moisture, and the ice begins to accumulate faster than the defrost cycle.
You should also avoid storing food in open containers without lids. The evaporation of moisture from soups, sauces and drinks increases the humidity inside the chamber, which accelerates the freezing of the heat exchanger.
Regular, at least once a year, cleaning in the refrigerator compartment with mandatory defrosting (disconnecting from the network for a day) will help remove contaminants from hard-to-reach places and check the operation of the drainage system. This will extend the life of the compressor and maintain cooling efficiency.
How often do you need to defrost a No Frost refrigerator?
Technically, you do not need to defrost a No Frost refrigerator to remove ice, since this is done automatically. However, complete defrosting (disconnection from the network for 24 hours) is recommended once every 1-2 years for hygiene, checking drainage holes and resetting electronic module errors.
Why does the refrigerator take a long time to reach temperature after defrosting?
After complete defrosting, there is a lot of moisture and heat inside the case. The compressor takes time (from 4 to 12 hours) to freeze this volume. Do not load food into an empty refrigerator immediately - let it go into idle mode.
Is it possible to operate the refrigerator if the defrosting heating element has burned out?
For a short time - yes, but not. Ice will gradually accumulate, block the ducts, the fan will begin to hum, and cooling efficiency will drop. As a result, the compressor will work without interruption, which will lead to its overheating and failure.
What does the "Ice Full" error or blinking indicators mean?
In many modern models (Bosch, Siemens, LG), electronics control the defrost time. If the sensor does not detect an increase in temperature within the allotted time, the module blocks operation and generates an error, indicating a malfunction in the defrost circuit.
Does the location of the refrigerator affect the operation of the evaporator?
Yes, critically. If the refrigerator is moved close to the wall, the heat exchange of the condenser (the grille at the back) is disrupted. The compressor is overloaded, the evaporator does not have time to cool properly, which disrupts the entire refrigerant circulation cycle. Leave a gap of at least 10 cm.