What is the difference between thermostats for refrigerators: types and choice

The temperature controller, often called a thermostat, is one of the key elements in the control system of a refrigeration unit. It is this small device that decides when to start the compressor to produce cold and when to stop it to avoid freezing the food. Owners of household appliances are often faced with the need to replace this part when the refrigerator stops freezing or, conversely, starts working continuously.

However, when purchasing a new spare part, it turns out that there are a huge number of models on the market that may look almost the same in appearance, but have critical technical differences. An incorrect choice can lead to unstable operation of the unit, frequent shutdowns or complete failure compressor. Understanding the operating principles and design features of these devices will help you avoid costly mistakes during repairs.

In this article we will look in detail at how thermostats differ from each other, what to look for when marking and how to choose an analogue for your refrigerator model. You will learn about the types of contacts, temperature ranges of operation and installation features of various modifications of regulators.

The principle of operation and the role of the thermostat in the system

The main task of any thermostat is to maintain the specified temperature conditions inside the refrigerator chambers. The device reads the temperature using a sensing element and opens or closes the electrical supply circuit to the compressor. Depending on the design, this sensitive element can be mechanical or electronic, which determines the main design differences between the models.

Mechanical thermostats use a bellows tube filled with gas or liquid. When the temperature changes, the pressure inside the tube changes, which leads to deformation of the bellows and mechanical opening of the contacts. Electronic models use thermistors, which change their resistance depending on the heating, transmitting a signal to electronic control board.

Differences in operating principles dictate different accuracy of temperature maintenance and reliability. Mechanical devices are considered more maintainable and resistant to power surges, while electronic ones provide more precise control, but require stable power.

⚠️ Attention: An attempt to replace a mechanical thermostat with an electronic one (or vice versa) without altering the refrigerator control circuit is impossible. These systems are incompatible based on the principle of interaction with the compressor.

How does a bellows tube work?

Inside the sealed thermostat tube there is freon or inert gas. When cooled, the gas contracts and the bellows retracts, opening the contacts. When heated, the gas expands, pushing the membrane and completing a circuit to start the motor. The length and volume of the tube are strictly calibrated for a specific model.

Types of contacts: normally closed and normally open

One ​​of the most important parameters by which thermostats differ is the state of their electrical contacts in the initial position. This is a critical point that must be taken into account when selecting spare parts. If you confuse the type of contacts, the refrigerator will either not turn on at all or will work constantly without stopping.

Most household refrigerators are equipped with thermostats normally closed contacts. This means that in normal conditions (at room temperature or when the thermostat is warm) the circuit is closed and current flows freely to the compressor. Opening occurs only when the temperature inside the chamber drops to a predetermined minimum.

There are also models with normally open contacts, which are used in specific circuits, for example, to control fans or signal lamps. In such devices, the circuit closes only when a certain temperature is reached. For the main control circuit of the motor-compressor in home refrigerators, such relays are practically not used.

• 🔌 Normally closed (NC): Standard for most refrigerators Atlant, Indesit, Stinol. The circuit is closed when the chamber is warm.
• 🔌 Normally open (NO): They are rarely used, mainly to control additional equipment or in industrial installations.
• 🔌 Universal: Some modern thermostats have a switchable group of contacts, but require correct switching during installation.

When visually inspecting an old thermostat, you can often see markings on the body, for example, “1-2” or “1-3”. The numbers indicate the contact numbers, and their connection diagram depends on the temperature. For a household technician, the most important thing is to know that when the sensitive tube (for example, in your hand) is heated, the contacts should click, changing their state.

Temperature ranges and markings

Each thermostat is designed to operate in a certain temperature range. This is perhaps the main difference, which directly affects the quality of food storage. If you install a regulator with the wrong range, the chamber may be too cold or, conversely, not cool enough.

The markings on the device body usually contain codes indicating the temperature thresholds. For example, popular TAM series thermostats may be designated L13, K59 or TAM-133. The numbers in the code often indicate the temperature at which the compressor turns on and off. Different manufacturers use different coding systems, which complicates the selection direct analogue.

There are thermostats for single-chamber refrigerators, where the range is usually from -10 to +10 degrees Celsius, and for two-chamber models, where a lower shutdown threshold is required, often down to -20...-24 degrees. Installing a thermostat from a single-chamber refrigerator to a two-chamber one will result in the freezer not reaching the desired temperature.

Below is a table with examples of common thermostats and their approximate temperature characteristics (data may vary depending on the manufacturer):

Design features: capillary tube length

Another critical parameter that distinguishes thermostats is the length and diameter capillary tube. It is this tube, sealed at the end, that is inserted into the refrigeration chamber and comes into contact with the evaporator or air. Its length determines how deep the sensor can be placed and how correctly it will read the temperature.

Standard tube lengths vary from 0.5 meters to 3 meters or more. If the tube is too short, you simply will not be able to reach the evaporator mounting point, and the thermostat will respond to the temperature in the incorrect zone. If the tube is excessively long, it will have to be twisted into a ring, which can lead to damage or incorrect heat transfer.

When replacing, it is important not only to choose a similar length, but also to pay attention to the method of fastening. In some models, the tube is simply pressed against the evaporator with a plate, in others it is inserted into a special socket. The diameter of the tube may also vary, although most often it is standardized for ease of installation.

⚠️ Attention: The capillary tube is filled with gas under pressure. It is strictly forbidden to bite, bend at an acute angle or damage its integrity. This will lead to leakage of the working fluid and complete inoperability of the thermostat.

Mounting methods and geometric dimensions

The geometry of the thermostat housing is what you will encounter first when dismantling. Differences in the shape of the case, the location of the mounting holes and wire leads can make the installation of even a technically suitable thermostat impossible without a “collective farm” and additional adapters.

There are thermostats with a flat case and with a protruding power button, as well as models where the button is combined with an adjustment knob. Fastening can be carried out with screws, latches or special metal plates. It is also important to consider the location of the contact group: the pins can look up, sideways or down.

Also pay attention to the presence of an additional grounding pin. In older refrigerator models, the thermostat housing was often grounded through a special screw on a metal plate. In modern models, this requirement is less common, but it cannot be ignored if the design provides for grounding.

• 📐 Dimensions: The height, width and depth should allow the device to be installed in its original location without deformation.
• 🔩 Fasteners: The distance between the screw holes must match the original.
• 🔌 Conclusions: The number and location of contacts must correspond to the connection diagram of your refrigerator.

Sometimes manufacturers produce universal thermostats, which are equipped with a set of adapter plates and extension tubes. This allows you to adapt the same model to different types of refrigeration units, which simplifies the logistics of spare parts for service centers.

Electronic thermostats versus mechanical ones

With the development of technology, electronic temperature control modules are increasingly found in refrigerators, which are radically different from the usual mechanical “turners”. The main difference is the absence of moving mechanical parts and a bellows tube in the classical sense.

In electronic systems, the temperature sensor is a small thermistor that can be located directly inside the air flow of the chamber. The signal from it is sent to electronic control unit (module), which already makes the decision to start the compressor. Such systems make it possible to more accurately maintain the temperature and implement complex algorithms, for example, the “Vacation” mode or quick freezing.

Replacing a mechanical thermostat with an electronic one is possible only with a complete rework of the refrigerator control system, which is not economically feasible. However, if your refrigerator originally had electronics, then you need to look for an electronic sensor or module, since a mechanical analogue cannot physically interact with the control board.

Tips for selecting and installing analogues

When looking for a replacement for a failed thermostat, it is not always possible to find original spare part with exactly the same markings. Fortunately, many thermostat manufacturers produce compatible analogues. The main thing is to comply with the basic technical characteristics.

First of all, focus on the temperature range and type of contacts. If you are not confident in your knowledge, it is better to use the correspondence tables (cross-codes) provided by spare parts manufacturers. For example, thermostats Ranco are often direct analogues for Danfoss or Thermo.

When installing a new thermostat, make sure that the capillary tube fits tightly to the evaporator. Poor contact will cause the sensor to read the temperature late, causing temperature fluctuations. To improve heat transfer, it is sometimes recommended to lubricate the contact point with a special heat-conducting paste, although this is rarely done in domestic conditions.

⚠️ Attention: Technical characteristics and compatibility of thermostats may vary depending on the year of manufacture of the refrigerator and modification. Always check the parameters with the documentation for your specific model or consult with the manufacturer of the spare part.

Frequently asked questions (FAQ)

You can Is it possible to install a thermostat with a longer tube than the original?

Yes, you can, but the excess length will have to be carefully rolled into a ring with a diameter of at least 5 cm and secured in the free space of the refrigerator compartment. The main thing is not to damage the tube or disrupt heat transfer.

Why does the new thermostat click, but the refrigerator does not turn on?

This may indicate a malfunction of the compressor start relay, the motor itself, or a problem with the wiring. It is also possible that a thermostat is installed with normally open contacts instead of normally closed ones.

How to check the serviceability of the thermostat without removing it from the refrigerator?

You can close the thermostat contacts directly (observing safety precautions). If the refrigerator starts working when the contacts are closed, then the problem is in the regulator. However, for accurate diagnosis, it is better to dismantle it and “ring” it with a multimeter when the temperature changes.

What is the difference between a thermostat for a refrigerator with No Frost and a regular one?

In No Frost systems, thermostats often have a wider operating temperature range and can be equipped with an additional defrost tube or have a specific setting for working with a defrost timer.