When the refrigerator stops turning off or, conversely, does not want to start the compressor, the thermostat becomes the first victim of suspicion. It is this small unit that is responsible for maintaining the specified temperature inside the chambers. In domestic models of refrigerators, such as Atlant, Nord or Biryusa, the device of the RTK-X-Mseries is most often found. Understanding the principle of its operation and diagnostic methods allows you to avoid calling a specialist and save your budget.
Failure of this element leads to damage to products or defrosting of the contents, so prompt verification is critical. In most cases, the breakdown lies in a violation of contact or loss of tightness of the bellows. Diagnostics Does not require complex equipment, just basic skills in working with electrical measuring instruments.
Before proceeding with disassembly, it is necessary to de-energize the unit. Any manipulation of electrical components without disconnecting from the mains carries the risk of a short circuit. Next, we will look in detail at how to remove the sensor, take measurements and interpret the results.
Design and principle of operation of a thermostat
Thermoregulator RTK-X-M is an electromechanical device that opens and closes an electrical circuit depending on the temperature. The main working element is bellows a sealed corrugated container filled with freon or other gas-filled substance. A capillary tube extending from the bellows is attached to the evaporator, transmitting temperature changes to the working gas.
When the temperature inside the chamber decreases, the gas is compressed, the pressure in the bellows drops, and the spring opens the contacts, stopping the compressor. When the temperature rises, the gas expands, pushes the membrane, and the contacts close, starting the cooling cycle. The model RTK-X-M also has a forced defrosting mechanism, which is controlled by a separate pair of contacts.
⚠️ Attention: The bellows and capillary tube are filled with refrigerant under pressure. It is strictly forbidden to bite, bend at an acute angle or heat the capillary tube, as this will lead to gas leakage and complete inoperability of the sensor.
The device body is usually made of dielectric plastic or metal and is equipped with three main terminals for connecting wires. The accuracy of operation depends on the calibration spring, the position of which is adjusted by a screw on the rod. It is this unit that often becomes the cause of incorrect operation if the factory settings have been reset.
Internal design
Inside the case there is a movable group of contacts, which, when triggered, makes a characteristic click. This sound indicates the mechanical serviceability of the moving parts, but does not guarantee the tightness of the bellows.
Diagnostics of external signs of malfunction
An initial assessment of the condition of the refrigerator can be carried out without the use of measuring instruments. There are a number of symptoms that most likely indicate a failure of the thermostat RTK-X-M. If you notice that the compressor is running continuously without turning off for hours, this is the first alarm signal.
Second scenario - the refrigerator is silent. The compressor does not start at all, although there is voltage in the network and the light inside is on. In this case, the control circuit may be broken due to the contacts sticking in the open position. The third sign is an incorrect temperature regime, when the food in the chamber either freezes or remains warm regardless of the position of the regulator knob.
- 🔊 The compressor hums constantly, but the temperature does not drop below +10°C.
- ❄️ A “fur coat” or an ice crust forms on the back of the refrigerator wall.
- 🔌 When turning the regulator knob, there is no characteristic click (although it may be barely audible).
- 🌡️ The temperature in the chamber does not correspond to the set value on the regulator.
It is important to distinguish a breakdown of the thermostat from a malfunction of the start relay or the compressor itself. If the motor hums, clicks and immediately turns off, the problem is most likely in the starter. If the motor is silent or hums endlessly without clicking off, then diagnostics begins by checking the thermostat contacts.
Removing the thermostat for testing
To carry out an accurate diagnosis with a multimeter, the thermostat must be removed from the refrigerator. The dismantling process depends on the specific refrigerator model, but the general algorithm of actions is similar for most devices with a series regulator RTK. First you need to gain access to the mounting location.
In refrigerators with a top freezer, the thermostat is often hidden under a plastic panel or located inside the chamber itself. In models type Nord or Atlant it may be necessary to remove the top cover of the housing or dismantle the lampshade. Be careful with plastic latches, they can be brittle from the cold.
After gaining access, disconnect the wires. It is advisable to first take a photo of the connection diagram or mark the wires with a marker so as not to mix up the contacts during assembly. The capillary tube must be carefully removed from the technological hole in the evaporator or chamber wall.
⚠️ Attention: When removing the capillary tube, do not use excessive force. If the tube is stuck or stuck, carefully treat the entry point with warm water, but do not use sharp objects so as not to damage the seal.
It is not necessary to completely remove the thermostat unit from the refrigerator body to check with a multimeter if the length of the wires allows it. However, for visual inspection of contacts and checking “continuity” in different temperature conditions, it is more convenient to work with a dismantled unit.
☑️ Dismantling algorithm
Checking the contacts with a multimeter
The most reliable method checks - use of an electronic tester (multimeter) in resistance (Ohm) measurement mode or continuity testing. On the body of the thermostat RTK-X-M there are usually three contacts. Two of them are the main ones (working), and the third is responsible for the defrosting function or indication.
First, you need to determine which contacts are working. In the “off” position (the knob is turned counterclockwise until it clicks), the circuit should be open. When turning the knob clockwise (turn on), the contacts should close. The resistance of a working pair of contacts in the closed state should be close to zero (0–2 Ohms).
If the multimeter shows one (infinity) when the regulator is in the on position, it means there is no contact - the device is faulty. If the device shows zero even in the “off” position, the contacts are stuck, which also requires replacement. The third contact is usually checked separately: it can close under certain conditions or remain open depending on the modification.
| Handle position | Expected state of the contacts | Multimeter readings (Ohm) | Diagnosis |
|---|---|---|---|
| Off (minimum) | Open | 1 (infinity) | Normal |
| Enabled (average) | Closed | 0–2 | Normal |
| Any position | Constantly closed | 0 | Sticking contacts |
| Any position | Permanently open | 1 (infinity) | Open circuit |
Special attention should be paid to the grounding contact (if there is one on the case) or the third pin. In some modifications RTK-X-M the third contact is used to connect a defrost lamp or indicator. Its testing requires specific conditions, but the main load lies on the main power contacts.
Checking the tightness of the bellows (Temperature test)
Electrical testing of the contacts is only half the battle. The thermostat may ideally “ring” with a multimeter, but not respond to temperature changes due to gas leakage from the bellows. To check this function, you need to place the sensitive element (capillary with bellows) in a low-temperature environment.
To do this, the dismantled thermostat (or only its capillary part, if the length of the wires allows) must be placed in the freezer compartment of a working refrigerator or in a container with ice and salt. The temperature should be below freezing, approximately -10...-15°C. Keep the device in the cold for 15–20 minutes.
After cooling, without removing the sensor from the cold (or quickly connecting the probes), check the resistance of the main contacts. In a cold state, a working thermostat should break the circuit (show one on the multimeter screen), simulating the achievement of the set temperature. If the contacts remain closed in the cold, it means that the gas in the bellows is not compressed - depressurization has occurred.
- 🧊 Place the capillary tube in the freezer for 20 minutes.
- 🔌 Connect the multimeter probes to the working contacts.
- 📉 In a cold state, the resistance should become infinite (break).
- 🔥 When heated to room temperature, the circuit should close again.
This method allows you to identify “lazy” thermostats that are formally working, but have a shifted response range. If the refrigerator turns off only when the food is severely overcooled, the problem is precisely in the calibration or loss of properties of the filler gas.
⚠️ Attention: When conducting a temperature test, make sure that moisture or condensation does not get on the contacts of the multimeter or the thermostat terminals. Water can create parasitic resistance and distort the readings of the device.
Replacing and setting up a new regulator
If the diagnostics revealed a malfunction, the thermostat RTK-X-M needs to be replaced. Repair by soldering or refilling with gas at home is neither possible nor economically feasible. When purchasing a new analogue, pay attention to the length of the capillary tube and the number of contacts - they must match the original.
Installation is carried out in the reverse order of dismantling. The capillary tube is carefully inserted into the technological hole, being careful not to damage it. It is important to ensure tight contact of the sensing element with the evaporator if the design includes a clamping bar. After assembling and turning on the refrigerator, it may be necessary adjustment.
Adjustment consists of selecting the optimal position of the handle. By rotating the rod, achieve an operating mode in which the refrigerator turns off after about 30–40 minutes of operation and stays for the same amount of time (with normal loading of the chamber). If the cycle is too short or long,
After replacement, it is recommended to monitor the temperature in the chambers using an external thermometer on the first day. This will ensure that the new regulator operates correctly and does not allow freezing or insufficient cooling.
⚠️ Attention: The characteristics of thermostats may vary slightly depending on the batch and manufacturer. If after replacement the refrigerator does not work correctly (turns on too often), you may need to install an analogue with other temperature thresholds.
Frequently asked questions (FAQ)
Is it possible to temporarily short-circuit the contacts to make the refrigerator work?
Yes, this is possible to check the compressor or how temporary measure (for 1-2 days). You need to connect the wires going to the main contacts of the thermostat. However, in this mode the refrigerator will operate continuously, which will lead to freezing of the evaporator and spoilage of food. Constant operation without a thermostat is dangerous for the compressor.
What is the difference between RTK-X-M and RTK-X-M-1-3?
The numbers at the end of the marking indicate the length of the capillary tube and the temperature range of operation. For example, suffix"-3" could indicate a longer tube or shifted shutdown thresholds. For household replacement, analogues are often suitable, but it is better to look for an exact match or a model with universal characteristics.
Why does the new thermostat click, but the refrigerator does not turn off?
Perhaps the sensitive element (capillary) is not pressed tightly enough to the evaporator and does not feel a real decrease in temperature. The cause may also be a malfunction of the compressor itself (loss of performance) or a refrigerant leak in the system, due to which the temperature does not drop to the shutdown threshold.
Where is the adjusting screw for calibration?
Inside the thermostat housing, on the rod coming out of the bellows, there is often a thread with a nut or screw Rotating this element changes the spring tension, shifting the temperature range. However, factory calibration is usually accurate, and it is worth interfering with it only if you have special equipment for measuring temperature.