Every refrigerator owner has at least once thought about how exactly a household appliance “understands” when to turn on the compressor and when to pause. The brain center of the cooling system is responsible for this intellectual process. Without this small but critically important unit, the refrigerator would turn into a useless box, unable to maintain a stable microclimate for storing food. thermostat, which is the brain center of the cooling system. Without this small but critical component, the refrigerator would turn into a useless box, unable to maintain a stable microclimate for storing food.
Complex physical processes of heat exchange always occur inside the chamber, which must be strictly controlled. It is thermostat (the second name of the device) that monitors the slightest changes in temperature in the evaporator or directly in the air of the fridge compartment. As soon as the indicators go beyond the specified limits, the mechanism closes or opens the electrical circuit, starting or stopping the operation of the motor-compressor.
Understanding the operating principle of this element is necessary not only for general development, but also for timely diagnosis of breakdowns. If you notice that the refrigerator has started to work without stopping or, conversely, is silent for too long, allowing food to defrost, the problem often lies precisely in temperature sensor. In this article we will examine in detail the internal structure, types of thermostats and methods for testing them.
The basic principle of operation of a mechanical thermostat
A classic mechanical thermostat is a sealed system filled with a temperature-sensitive gas or liquid. The main working element here is a bellows tube (bellows) - a corrugated container capable of changing its volume under the influence of pressure inside it. When the temperature in the chamber rises, the working substance expands, creating excess pressure on the walls of the bellows.
This pressure is transmitted to the lever system, which mechanically closes relay contacts. At this moment, electric current enters the compressor winding, and the refrigerator begins to cool the space. The process continues until the temperature drops to the lower limit. At this moment, the pressure inside the bellows drops, the spring expands, and the contacts open, stopping the cooling cycle.
⚠️ Attention: The sensitivity of a mechanical thermostat depends on the integrity of the capillary tube. If even a microscopic leak of freon filler occurs in the system, the thermostat will stop responding to temperature changes, and the compressor will either not turn on at all or will work continuously.
It is important to note that the desired temperature is set by the user manually, usually using a rotary knob inside the chamber. By turning the adjuster, you change the tension of the main spring, which requires more or less pressure from the bellows to close the contacts. This allows flexible control temperature range depending on the load of the refrigerator and the time of year.
Electronic sensors: a modern approach to control
In modern models of refrigerators, especially in systems No Frost and devices with inverter compressors, mechanics give way to electronics. Here, instead of bellows and gas, thermistors (NTC sensors) are used. Their operating principle is based on a change in the electrical resistance of the material depending on its temperature. The colder, the higher the resistance, and vice versa.
The electronic control module constantly scans the state of the sensors, receiving accurate digital data about the climate in each zone of the refrigerator. This allows the system to work much more efficiently, minimizing temperature changes that are inevitable when using mechanical analogues. Electronics is able to take into account many factors: fan operation, defrosting state, frequency of door openings.
- 🔹 High accuracy of maintaining specified parameters without manual adjustments.
- 🔹 Possibility of independent temperature control in the refrigerator and freezer compartments.
- 🔹 Integration with diagnostic systems and displaying errors on the display.
- 🔹 Less physical wear, since there are no moving mechanical parts.
Despite the reliability, electronic components are sensitive to power surges. If your refrigerator stops responding correctly to settings or shows the wrong temperature on the display, first of all you should check thermal sensor with a multimeter. Replacing such an element often requires disassembling the inner lining of the chamber, which is more difficult than replacing a mechanical analogue.
Why are electronics more accurate than mechanics?
A mechanical thermostat has a hysteresis (the difference between turning on and off) of several degrees, which leads to noticeable temperature fluctuations. The electronic sensor reacts instantly, allowing the control module to turn on the compressor in short pulses to maintain ideal mode.
Design features and arrangement of elements
The location of the thermostat depends on the type of refrigerator and the year of its manufacture. In older models, such as Atlant or Biryusa, the control unit is often placed outside, on the top of the body, and the capillary tube is attached to the evaporator inside the chamber. In more modern built-in and two-chamber models, the thermostat can be hidden behind a plastic panel or even built into the electronic control unit.
The key design element is capillary tube. This is a thin copper or aluminum conductor that connects the bellows to the sensitive area. It can be simply attached to the surface of the evaporator or embedded in a special channel. The length and method of attachment of the tube are critical: if it does not fit well to the heat exchanger, the readings will be incorrect.
Double-compartment refrigerators with one compressor often use a system where the thermostat controls the temperature in the freezer compartment, and the flow of cold air into the refrigerator compartment is regulated by a damper. This scheme saves energy, but requires precise calibration damper mechanism and correct positioning of the sensor.
| Thermostat type | Sensing element | Accuracy | Difficulty of replacement |
|---|---|---|---|
| Mechanical | Bellow with gas/liquid | Low (±2-3°C) | Low |
| Electronic (NTC) | Thermistor | High (±0.5°C) | Medium/High |
| Pneumatic | Membrane and air | Average | Average |
Typical faults and their symptoms
Diagnostics of problems with the thermostat often begins with an analysis of the behavior of the compressor. If the motor hums continuously without turning off for hours, this is a sure sign that relay contacts it is stuck in a closed state or the bellows has lost its seal and is not creating enough pressure to open the circuit. In this case, the food in the refrigerator compartment may freeze.
The opposite situation, when the refrigerator does not turn on at all or turns on for a very short time, also indicates a malfunction of the thermostat. The contacts may oxidize and stop conducting current, or the spring of the mechanism may weaken. In electronic models, an open circuit of the temperature sensor often leads to the control module going into emergency mode and blocking the start of the compressor to avoid damage to products.
- ❄️ A thick “coat” of ice forms on the back wall of the refrigerator compartment.
- 🔊 The compressor operates with short cycles (often on and off).
- 🌡️ The temperature in the chamber is significantly higher or lower installed.
- 💡 The light inside is constantly on (if it is tied to the door and thermostat), or goes out when the door is open.
Particular attention should be paid to the condition of the capillary tube. If it is accidentally pinched during installation or has traces of corrosion, this will lead to incorrect operation of the entire system. A visual inspection often helps to identify obvious defects, however, for accurate diagnosis it is required contact testing a tester under different temperature conditions.
⚠️ Attention: Before any diagnostics or replacing the thermostat, be sure to disconnect the refrigerator from the power supply! Working with live electrical components is dangerous and can lead to a short circuit.
Instructions for checking and replacing the thermostat
The process of replacing a mechanical thermostat is not technically difficult, but requires care. The first step is always to dismantle the old device. To do this, remove the regulator handle, unscrew the fastening screws and carefully remove the unit, being careful not to damage capillary tube. It is important to remember or photograph the wiring diagram, since the color markings may differ from one manufacturer to another.
The new thermostat should have similar characteristics and markings. Place the device in place, secure it and carefully straighten the capillary tube, fixing it in its normal place on the evaporator. Use special clamps or heat-resistant tape if the design provides for it. Loose contact of the tube with the surface of the evaporator will lead to incorrect operation.
☑️ Algorithm for replacing the thermostat
After assembly, it is necessary to check the tightness of the connections and the functionality of the system. Turn on the refrigerator and wait for the first cooling cycle. If the compressor turns off after reaching the desired temperature, it means the replacement was successful. Otherwise, additional adjustment of the screws on the thermostat body may be required, but this is recommended only by specialists with the appropriate equipment.
Setting and calibrating temperature conditions
Correctly setting the thermostat can extend the life of the compressor and ensure optimal storage conditions. For mechanical models, there is a “golden rule”: in summer the knob should be set to average values, and in winter, if the refrigerator is in an unheated room, you may need to use a special winter mode (if it is provided by the model).
Calibration of electronic systems usually occurs automatically, but the user can adjust the settings through control panel. It is recommended to check the actual temperature using an external thermometer placed in a glass of water. This will allow you to understand how accurately electronic sensor transmits data and whether there is a need for service intervention.
You should not set the minimum possible temperature unless absolutely necessary. Operating the compressor at its limit leads to accelerated wear of the oil and mechanical parts. The optimal mode for the refrigerator compartment is considered to be from +3 to +5 degrees Celsius, and for the freezer compartment - about -18°C.
The influence of external factors on the operation of the thermostat
The operation of the thermostat directly depends on environmental conditions. If the refrigerator is located next to a radiator or in direct sunlight, the sensor will register an increased temperature and force the compressor to work harder. This leads to excessive consumption of electricity and a reduction in the resource of cooling system.
It is also important to take into account the climate class of the refrigerator. Devices designed for moderate climates may not work properly in hot conditions or, conversely, in a cold garage. In the latter case, the oil in the compressor thickens, and the thermostat may not give a start command at all, since the temperature in the chamber is already low.
⚠️ Attention: Technical characteristics and control interfaces may vary depending on the specific model and year of manufacture. Always check the manufacturer's official instructions (user manual) before carrying out complex manipulations or settings.
Frequently asked questions (FAQ)
Is it possible to repair a mechanical thermostat or just replace it?
In most cases, mechanical thermostats are non-separable devices. An attempt to open the housing and bend the springs often leads to a violation of the tightness of the bellows and final failure. Professional repairs are possible only in specialized workshops with the replacement of the sensitive element, but it is more economically feasible to buy a new part.
Why does the refrigerator click but does not turn on?
A click usually means that the thermostat is trying to start the compressor by closing the contacts. If the motor does not start, the problem may be with the compressor start relay, the motor itself, or sticking contacts inside the thermostat itself. Diagnostics with a multimeter is required.
How to check an electronic temperature sensor without replacing it?
To check the electronic temperature sensor (thermistor), you need to remove it and measure the resistance with a multimeter at room temperature, and then cool it (for example, by putting it in the freezer for a few minutes). The resistance should change smoothly. If the readings are absent or do not change, the sensor is faulty.
Does defrosting affect the operation of the thermostat?
Regular defrosting is necessary for refrigerators with a drip system so that the ice does not isolate the sensitive element of the thermostat. If the evaporator is covered with a thick layer of ice, the sensor stops reading the temperature correctly, which leads to failures in the cooling cycles.