The question of correctly setting a thermostat or choosing an analogue during repairs often confuses even experienced home craftsmen. Many people confuse the concepts of electrical power of a compressor and thermodynamic power (performance) of the refrigeration unit itself, which leads to diagnostic errors. Understanding how these parameters interact is critical to ensuring stable operation of household appliances.
When the refrigerator stops freezing or, conversely, turns food into ice, the first thought is to turn the regulator. However, the mechanical knob you turn does not directly control the motor's power in the traditional sense of the word. It only sets the temperature threshold for the relay to operate, which opens or closes the electrical circuit.
There is a common misconception that you can simply take any thermostat and screw it in, choosing the “power” empirically. This is a dangerous approach, since each one thermostat is calibrated for a specific refrigerant and evaporator volume. Incorrect settings can lead to a constant working compressor without shutting down or, conversely, to too infrequent starts, which is detrimental to the safety of products.
The difference between electric and refrigeration power
Before understanding the settings, it is necessary to clearly separate two fundamental concepts. Electrical power is measured in Watts and indicates the energy consumption of the motor. Refrigerating power is measured in Watts of cold or kcal/hour and shows how much heat the unit is able to remove from the chamber per unit of time.
The thermostat, whether mechanical K-59 or an electronic module, does not regulate the speed of rotation of the compressor shaft (with the exception of inverter models, where control occurs differently). Its task is to control the temperature of the evaporator. When the sensor detects that the specified minimum has been reached, it turns off the power. When the temperature rises to the upper threshold, it turns on the motor again.
⚠️ Attention: An attempt to replace the thermostat with a model with a different operating temperature range without resetting may lead to freezing of the evaporator or overheating of the compressor due to the lack of pauses in operation.
It is important to understand that “power” in the context of setting is, in fact, sensitivity and response range. If you place a freezer-rated regulator in the refrigerator compartment, the system will not work correctly. The shutdown temperature may be too low, which will cause continuous operation of the equipment.
How the thermostat works in the system
The principle of operation of a classic mechanical thermostat is based on the expansion and compression of gas or liquid inside the bellows of a capillary tube. The end of this tube is attached to the evaporator. When the temperature changes, the pressure inside the system changes, which mechanically opens or closes the contacts.
The “power” or temperature range is adjusted using special screws hidden under a seal or plastic plug. One screw regulates the switch-on temperature, the other regulates the difference between switch-on and switch-off (differential). The third may be responsible for the shutdown temperature.
In modern models with the system No Frost the process looks more complicated, since the sensors are often electronic. However, the logic remains the same: the controller receives temperature data and supplies voltage to the compressor. An error in choosing the type of sensor (resistance) will lead to incorrect readings on the display.
Why can’t you ignore the type of refrigerant?
Thermostats are marked with letters indicating the type of refrigerant (K, L, R). Using the wrong regulator will result in the refrigerator either constantly thrashing or not turning on at all, since the vapor pressure of the refrigerant is different at different temperatures.
The influence of the type of refrigerant on the settings
A critically important parameter that many ignore is the type of refrigerant for which the thermostat is designed. Different gases (freons) have different physical properties, in particular, the dependence of saturation pressure on temperature. It is to this pressure that the thermostat bellows reacts.
If the system circulates R134aand the thermostat is calibrated for R600a (isobutane), then at the same temperature inside the chamber the pressure in the bellows will be different. This will lead to a shift in the temperature range. The refrigerator may turn off at -5°C instead of the required +4°C, defrosting food, or not turn off at all.
The labeling of thermostats usually contains information about compatibility. For example, the TAM series is often used in household refrigerators, but has different modifications. Professional repairs require checking the factory parameters with the actual readings of the pressure manifold.
Correspondence table of thermostats and refrigerants
To simplify the selection of components for During repairs, it is recommended to use reference data. Below is a table showing the dependence of the choice of component on the type of gas and temperature conditions.
| Refrigerant type | Thermostat series | Shut-off range (°C) | Application |
|---|---|---|---|
| R134a | K-59 / K-56 | -24...-28 | Freezers |
| R600a | K-50 / K-57 | -10...-14 | Refrigerator compartment |
| R12 (old) | TAM-112 | -20...-24 | Single-chamber models |
| R404A | K-61 | -30...-35 | Industrial chambers |
The data in the table is for reference only, as equipment manufacturers can use non-standard solutions. Always check the markings on the old thermostat housing before purchasing a new one. The numbers at the end of the code (for example 3366 or 3348) often indicate the length of the capillary tube and the temperature range.
Note that the length of the capillary tube also plays a role. If the tube is too short, the sensitive element may not have time to respond to changes in the temperature of the evaporator, which will lead to cycling (frequent on-off) of the compressor.
Algorithm for setting and adjusting the screws
If you decide to adjust the existing thermostat, you will need access to the adjusting screws. Usually there are three of them, but it is recommended to twist only those whose position you have fixed before starting work. It is best to take a photo or sketch the starting position.
The setup process takes time and patience. After each turn of the screw (usually 1/4 or 1/2 turn), it is necessary to allow the refrigerator to return to operating mode. This can take from 30 minutes to several hours depending on the load of the chamber and the ambient temperature.
☑️ Procedure for adjusting the thermostat
First adjust the shutdown temperature. If the refrigerator turns off too early (it is warm in the chamber), turn the range screw in the direction of increasing numbers (or clockwise if there is no marking). If it freezes too much, downward.
⚠️ Attention: Adjusting the differential (temperature difference) without professional tools is dangerous. A differential that is too small will result in frequent engine starts, which will burn out the start relay or windings.
For precise adjustments, you need an external thermometer placed in a glass of water in the center of the chamber. The readings from the built-in regulator are often inaccurate. Your goal is to turn off the compressor at +4...+5°C in the refrigeration chamber and turn it on at +6...+7°C.
Diagnostics of power regulator faults
How to understand that the problem is in the thermostat, and not in a freon leak or a compressor malfunction? There are a number of characteristic features. If the compressor runs continuously, but the cold does not accumulate, or vice versa - there is silence, although it is warm in the chamber, suspect first the thermostat.
One of the simple testing methods is to close the contacts. If, when the thermostat wires are shorted (bypassing it), the compressor starts and the refrigerator begins to freeze, it means that the motor itself and the freon are in order, and the regulator does not give a signal to turn on.
- 🔌 The compressor hums, but does not start: perhaps the thermostat does not supply voltage, or the problem is in the start relay. Checking the voltage at the thermostat contacts is mandatory.
- ❄️ The refrigerator has turned off and does not turn on: if there is voltage in the socket and a working power cord, an open circuit inside the thermostat is likely.
- 💧 Severe freezing of the rear wall: indicates that the thermostat “does not see” the cold and does not turn off the compressor in time. The sensor could have moved or failed.
It is also worth checking the integrity of the capillary tube. If it is pinched, flattened or damaged, the gas inside it may have escaped and the bellows will no longer respond to temperature. Visual inspection of the tube leading to the evaporator often reveals mechanical damage.
Common mistakes when choosing analogues
When searching for a replacement part, many users focus only on the appearance and fit dimensions. This is a big mistake. Even if a new thermostat fits perfectly in place of the old one, its internal characteristics may differ radically.
For example, installing a thermostat with a lower shutdown threshold in a refrigerator designed for high temperatures will lead to the unit working for wear, trying to achieve an unattainable minimum. This is a direct path to compressor failure.
In addition, it is important to consider the length of the capillary tube. If the new tube is much longer, its excess cannot be twisted into a tight ball, as this will disrupt the heat transfer and inertia of the system. The excess length is carefully laid with a snake in the free space of the case.
⚠️ Attention: The characteristics of thermostats may vary depending on the batch and manufacturer. Before installation, check the markings and, if possible, test the new component on a bench or with a multimeter.
The use of universal thermostats with a wide setting range is possible, but requires careful calibration. They often have a wider differential, which may be undesirable for some refrigerator models where precise temperature maintenance is required.
FAQ: Frequently Asked Questions
Is it possible to temporarily short-circuit the thermostat to make the refrigerator work?
Yes, this is possible for diagnostics or as a temporary measure (for a few days). Closing the contacts will cause the compressor to run continuously. However, this is dangerous: without temperature control, the evaporator can freeze into stone and the compressor can overheat. Use this circuit only under supervision.
Why does the new thermostat click but does not turn on the compressor?
The click means that the mechanics are working, but there is no contact. Possible reasons: the contacts inside are burnt due to a power surge, the compressor starting relay is faulty, or the compressor itself has a broken winding. It is necessary to test the circuit with a multimeter.
Does the temperature in the room affect the power setting?
Yes, indirectly. In a hot room, it is more difficult for the refrigerator to transfer heat through the condenser, so operating cycles may be longer. Some thermostats have a climate class. If the room is very cold (below +10°C), a regular refrigerator may not turn on at all, since the sensor “thinks” that it is already cold.
How often should the thermostat be changed?
The service life of a high-quality thermostat is 10-15 years or more. It does not have a certain resource in hours, like a compressor. Replacement is made only in the event of a malfunction: it does not hold the temperature, does not turn on or off.