To ensure the safety of products and the correct operation of refrigeration equipment, it is critical to understand the physical processes occurring inside the chambers. The main element of the cooling system is the evaporator - a heat exchanger in which the refrigerant boils, removing heat from the internal volume of the unit. It is on the efficiency of the operation of this unit that it depends on how stable it will be the temperature of the evaporator in the refrigerator and whether the device will be able to maintain the specified mode.
Many owners of household appliances are faced with the problem of the formation of a snow coat or, conversely, insufficient cooling, not suspecting that the root of the problem lies in the disruption of heat exchange in the refrigerator. radiator surface. Under ideal conditions, the operating temperature of the evaporator surface should be well below the freezing point of water, which allows for efficient heat removal even when the humidity inside the chamber is high. However, actual indicators depend on many factors, including the type of refrigerant, thermostat settings and serviceability of sensors.
In this material we will analyze in detail what temperature values are considered normal for various models, why deviations occur and how to independently carry out initial diagnostics of the system. Understanding these processes will help you avoid costly repairs or notice a compressor malfunction in time. We will also look at the differences between static systems and technology No Frost, since the principles of operation of their evaporators are significantly different.
The principle of operation of the evaporator and the physics of the process
The evaporator is a complex system of tubes through which refrigerant circulates under low pressure. Entering this unit from a throttling device (capillary tube or expansion valve), liquid freon expands sharply and boils. At this moment, intense absorption of heat from the surrounding space occurs, which leads to strong cooling of the metal walls of the tubes and the plates attached to them. Boiling point The refrigerant at this moment can reach extremely low values.
Moisture from the air condenses on the surface of the cold evaporator, which instantly turns into frost. In a working refrigerator, this process is strictly controlled: in models with a drip defrost system, the ice periodically melts when the compressor stops, and in systems No Frost a special heating element is turned on. If the balance between cold production and defrosting is disturbed, the surface temperature begins to behave unpredictably, which leads to freezing of the channels or overheating of the compressor.
It is important to understand that heat transfer depends not only on the operation of the compressor, but also on the tightness of the circuit. If freon leaks, the pressure in the system drops, the boiling point shifts, and the evaporator stops cooling at full capacity, even if the compressor runs continuously. In such cases freon boiling point becomes higher than calculated, which makes cooling ineffective.
Why is ice a poor conductor of heat?
Ice has very low thermal conductivity compared to metal. A thick layer of frost on the evaporator acts as a heat insulator, preventing cold from penetrating into the chamber, which causes the compressor to work hard, trying to compensate for losses.
Normal temperature readings for different systems
The answer to the question of what evaporator temperature in a refrigerator is considered normal directly depends on the type of cooling system installed and the type used refrigerant. For classic single-compressor models with a drip defrost system, the evaporator surface temperature at the time of active compressor operation usually varies in the range from minus 5 to minus 15 degrees Celsius. This is enough to maintain +3...+5 °C in the main chamber.
In freezers and dual-circuit systems, the figures are significantly lower. Here evaporator temperature it can drop to minus 20...minus 24 °C and even lower, depending on the settings of the “Super Freeze” mode. In systems No Frostwhere one powerful evaporator cools the entire volume through air channels, the temperature on the radiator is also extremely low, but the air is supplied to the chamber already mixed and heated to the required values.
It is worth noting that modern inverter compressors operate in a more gentle mode, maintaining the evaporator temperature in a narrow corridor without sudden changes. This reduces energy consumption and noise levels. However, during initial startup or after defrosting, the temperature difference can be significant until the system reaches operating cycle.
⚠️ Attention: Do not attempt to measure the temperature of the metal surface of the evaporator with sharp objects or ice picks. Damage to the tube will lead to the immediate release of freon and the entry of moisture into the system, which will require complex evacuation and replacement of the filter-drier.
Below is a table of approximate temperature conditions for various components of the refrigeration system:
| Unit type / Mode | Surface temperature (min.) | Surface temperature (max.) | Note |
|---|---|---|---|
| Refrigeration chamber evaporator | -15 °C | -5 °C | Drip system |
| Evaporator freezer | -26 °C | -18 °C | Storage mode |
| Evaporator No Frost | -25 °C | -15 °C | Behind the air damper |
| Condenser (grid at the back) | +40 °C | +60 °C | High pressure zone |
Symptoms of malfunctions: freezing and ice
One of the most common signs of a temperature violation is excessive freezing. If you notice that the back wall of the refrigerator is covered with a thick layer of ice, and food is frozen to the shelves, this indicates that evaporator temperature too low or the defrost cycle is not starting. In systems No Frost this often leads to complete blocking of the air channels, and the cold stops flowing into the chamber, although the compressor hums continuously.
The other extreme is the situation when the evaporator remains warm or is covered with frost only at the entrance of the tube, and the rest dry. This is a classic sign of a refrigerant leak or a clogged capillary tube. In the first case, the pressure in the system drops and the freon evaporates too early, not reaching the end of the circuit. In the second, circulation stops completely, and refrigerant boiling does not occur in the required volume.
It is also worth paying attention to the nature of defrosting. If, after defrosting, the refrigerator begins to quickly become overgrown with ice again (within a few hours), the problem may lie in a malfunction of the defrost sensor or timer. The electronics “does not see” the ice or does not give a command to turn on the heating element, believing that the evaporator temperature is normal, although in fact the heat exchange is disrupted.
Diagnostics of the thermostat and sensors
The key element regulating temperature in the refrigeratoris a thermostat (thermostat) or an electronic sensor. It is these devices that command the compressor to turn on or off. If the thermostat is mechanical, its capillary tube should be in close contact with the evaporator. The displacement of the tube leads to the fact that the sensor measures the temperature of the air, not the surface, which causes incorrect operation:
- ❄️ The compressor does not turn off, causing deep freezing of products.
- ❄️ The unit turns off too early, without gaining the required cold.
- ❄️ There is a large temperature spread (hysteresis), when the difference between turning on and off is 10-15 degrees.
In electronic models, thermistors (NTC sensors) are responsible for control. Their resistance changes depending on heat. If the sensor “lies”, the controller receives incorrect data about what is the evaporator temperature at the moment and generates erroneous commands. Checking such elements requires a multimeter: it is necessary to measure the resistance at different temperatures and compare it with the table for a specific model.
Often the cause of failures is not the sensor itself, but oxidation of the contacts in the connector or damage to the wiring. Over time, compressor vibration can break contact, and the system will go into emergency mode or simply stop responding to changes in thermal conditions. Visual inspection of the wiring harnesses in the evaporator area often helps to find a break.
☑️ Diagnostics of the defrost system
The influence of the refrigerant on the boiling point
The type of refrigerant used directly affects the physical parameters system operation. Old models running on R12 (Freon-12) had the same operating pressures and boiling points.