Modern refrigerators, especially models with the No Frost system, are complex electronic devices, where each element plays a critical role in maintaining the temperature. One of the key components that ensures stable operation of the defrost system and accurate temperature control is thermistor, which is often referred to in technical documentation as RKT. Owners of equipment may be faced with a situation when an error code associated with a temperature sensor lights up on the display, or the refrigerator begins to work incorrectly, for example, it freezes food or, conversely, does not cool the chamber sufficiently.
The abbreviation RKT stands for "silicon thermometric resistor", and the number "2" in the marking usually indicates a specific size, resistance rating or installation location depending on the electronics manufacturer. Checking RKT 2 - this is a procedure that is accessible even to non-professionals, if you follow safety precautions and have a minimum set of tools on hand. Understanding the operating principle of this element will allow you to independently diagnose the malfunction and avoid an expensive call to a technician to simply replace the part.
Before proceeding with active diagnostics, you must clearly understand that this sensor is a passive element that changes its electrical resistance depending on the ambient temperature. If you notice that your Atlant refrigerator, LG or Samsung is behaving strangely, you should not immediately blame the compressor or a freon leak. Often the problem lies precisely in incorrect sensor readings, which is why the control module receives false data and makes incorrect decisions about turning on or off the defrost heater.
What is RKT 2 and where is it located in the refrigerator
The RKT 2 thermistor is a compact element enclosed in a sealed housing, often resembling a small tablet or cylinder with two outgoing wires. Its main task is to transmit information about the current temperature in the evaporator or in the refrigeration chamber to the electronic control module. Unlike old mechanical thermostats, electronic sensors provide much higher measurement accuracy, which allows the compressor to operate in optimal mode, saving energy.
The location of the RKT 2 sensor depends on the specific model of the refrigeration unit and its functionality. In systems with fully automatic defrosting (No Frost), this element is most often mounted directly on evaporatorhidden behind the back wall of the freezer. It is here that he controls the ice defrosting process. In two-chamber models with one compressor, a second similar sensor may be located in the refrigerator compartment to control the air temperature.
It is important to understand that the “RKT 2” marking can be found in refrigerators of different brands, but their physical dimensions and ratings may differ. For example, in technology Indesit or Ariston this component is often installed in a plastic casing on the evaporator, while in models Beko it can be built into a special groove.
Why do sensors fail?
The main reason The failure of thermistors is the natural wear of the material as a result of constant heating and cooling cycles, as well as oxidation of the contacts in conditions of high humidity. Less commonly, the cause is mechanical damage during defrosting or a power surge.
⚠️ Attention: Before any manipulations inside the refrigerator related to removing panels and accessing electrical components, be sure to disconnect the appliance from the power supply. Working with live wiring is strictly prohibited and dangerous to life.
Symptoms of malfunction of the RKT thermistor
Diagnosis of any malfunction should begin by observing the behavior of the equipment. If the RKT 2 sensor fails or begins to transmit distorted data, the refrigerator will react in predictable ways. The electronic control unit, receiving incorrect signals, will not be able to correctly control the operating cycles of the compressor and defrost heater.
The most common sign of a breakdown is the appearance error code on the digital display or blinking of temperature indicators. The codes vary from manufacturer to manufacturer: it may be a flashing “Alarm” light, a combination of symbols on the screen, or a specific sound signal. However, you should not rely only on electronics, since the sensor can “lie” within acceptable values, without causing an alarm, but disrupting operation.
Pay attention to the following indirect signs:
- ❄️ Formation of excessive “fur coat” or ice in the freezer, even if the door closes tightly.
- 🌡️ Inconsistency between the actual temperature and the set values (food freezes in the refrigerator compartment or, on the contrary, spoils).
- 🔊 Continuous or too frequent operation of the compressor without sufficient pauses for rest.
- 💧 The appearance of puddles water under the refrigerator or inside the chambers due to problems with draining melt water.
If you find that the evaporator is completely covered with ice, but the defrost heater is working, then with a high degree of probability the problem lies precisely in defrost thermistor. It does not give a signal to the module that there is no more ice and it is time to stop heating, or vice versa - it does not initiate defrost on time.
Necessary tools for checking the sensor
To carry out high-quality diagnostics, you do not need a complex professional stand, a basic kit for a home technician is enough. The key tool here is multimeter (tester), which allows you to measure resistance. Without this device, the check will be only indirect and will not give an accurate result.
In addition to the measuring device, you will need:
- 🔧 A set of screwdrivers (phillips and flat) for dismantling panels and protecting the evaporator.
- ✂️ Pliers or wire cutters for working with wires (if replacement is required).
- 🔥 Hairdryer (construction or household) or a container of hot water to change the temperature of the sensor during the test.
- 📱 Smartphone with a camera to record the original position of the wires and fasteners before disassembly.
Make sure that the multimeter is in working order and its batteries are charged. To test thermistors, the resistance measurement mode in the range from 1 kOhm to 100 kOhm is usually used. If your device has a "test" mode, it will help you quickly determine the presence of an open circuit, but will not provide information about the current resistance.
It is also recommended to prepare a container for storing small fasteners so as not to lose screws during disassembly. In some refrigerator models, access to the RKT 2 sensor may be difficult, and partial disassembly of the inner lining of the chamber will be required.
Step-by-step instructions: how to check RKT 2 with a multimeter
The testing process begins with access to the sensor itself. In No Frost refrigerators, this usually requires defrosting the chamber for 10-12 hours (if there is a lot of ice), removing the back panel in the freezer compartment and finding the evaporator itself. The RKT 2 sensor is usually attached to the fins of the evaporator or inserted into a special hole in its body.
After you have reached the component, perform the following steps:
- Disconnect the sensor connector from the main control board or from the wiring harness. Do not try to measure resistance without disconnecting the sensor from the refrigerator network, otherwise the readings will be incorrect.
- Turn the multimeter into resistance measurement mode (Ohm).
- Connect the tester probes to the contacts of the RKT 2 sensor. Polarity in this case does not matter, since this is a symmetrical element.
- Fix the readings on the device screen at room temperature.
The normal resistance at room temperature (about +20...+25°C) for most RKT type sensors is from 4 to 7 kOhm. However, the exact values depend on the specific model. If the multimeter shows one (infinity), it means it is in the sensor break. If it shows zero, it happened short circuit. In both cases, the part must be replaced.
☑️ Algorithm for checking the thermistor
For deeper diagnostics, you can check the change in resistance when temperature change. Warm the sensor in your hands or blow warm air from a hair dryer on it. The resistance of a working thermistor should gradually decrease when heated. If the readings “jump” or do not change at all, the element is faulty.
Table of typical resistance values
To help you more accurately interpret the readings of your tester, below is a table with approximate resistance values for common types of thermistors used in refrigeration equipment. Remember that small deviations are acceptable, but they should not be critical.
| Sensor type / Temperature | Resistance at 0°C | Resistance at +25°C | Resistance at +50°C |
|---|---|---|---|
| RKT (standard) | ~13-15 kOhm | ~5-6 kOhm | ~2-3 kOhm |
| RKT 2 (modified) | ~10-12 kOhm | ~4.5-5.5 kOhm | ~1.8-2.5 kOhm |
| Defrost sensor (universal) | ~14 kOhm | ~6 kOhm | ~2.5 kOhm |
| fridge compartment sensor | ~20 kOhm | ~8-9 kOhm | ~3-4 kOhm |
As can be seen from the table, the resistance decreases with increasing temperature. This is typical for negative temperature coefficient (NTC) thermistors, which are most often designated as RKT. If your measurements differ radically from the table (for example, at +25°C it shows 50 kOhm or 0.5 kOhm), then the part is defective.
Replacing the RKT 2 sensor: nuances and features
If the check shows a malfunction, the only solution is replacing the sensor. Repairing the thermistor itself is impossible, since it is a sealed element. When purchasing a new part, try to find an original or a high-quality analogue with identical characteristics. Installing “by eye” or using a sensor from another model can lead to incorrect operation of the entire system.
The replacement process is usually not difficult:
- 🛠️ Carefully remove the old sensor from its seat. Often it is simply inserted into the hole or secured with a clip.
- 🔌 Connect the new connector. If the connectors do not fit, you will have to connect the wires by twisting, followed by soldering and heat-shrink insulation.
- 🧊 Place the sensor in place, making sure that it fits tightly to the surface being measured for accurate readings.
- 🔌 Reassemble the structure in reverse order and turn on the refrigerator.
⚠️ Attention: When connecting wires inside the wet chamber of the refrigerator, use only high-quality insulation. Regular electrical tape can peel off over time due to moisture and cold, causing a short circuit. It is best to use heat-shrinkable tubes.
After replacement and assembly, you must start the refrigerator and let it run a full cycle. During the first hours of operation, a longer operating time of the compressor is possible, since the system needs to reach the specified temperature regime. Make sure there are no error codes on the display.
Frequently asked questions (FAQ)
Is it possible to temporarily operate a refrigerator with a faulty RKT 2 sensor?
Operation is possible, but not advisable. If the sensor “lies” in the lower direction, the refrigerator may not turn on the defrost, which will lead to ice fouling on the evaporator and eventual breakdown of the compressor due to overload. If it is too long, the food may defrost.
Why does the new sensor not eliminate the error on the display?
There may be several reasons: the new sensor itself is faulty (defective), there is a break in the wiring between the sensor and the board, or the problem lies in the electronic control module itself. Also, the error could be “stuck” in memory and requires a reset (disconnection from the network for 15-20 minutes).
What is the difference between an RCT sensor and a thermostat?
A thermostat is a mechanical circuit breaker that simply turns the current on and off at a certain temperature. RCT is an electronic component that transmits accurate temperature data in the form of resistance, which allows a “smart” controller to flexibly control processes.
How to determine which sensor is faulty if there are several of them?
You need to know the error codes of your brand of refrigerator. Typically, error F1, F2 or E1 indicates a specific sensor (for example, in the freezer), and F3, F4 indicates another (in the refrigerator compartment). The decoding of the codes should be found in the instructions for the specific model.