Sudden breakdown of the refrigeration unit often takes you by surprise, causing you to panic about the safety of your food. However, before calling a specialist or buying new equipment, it is worth conducting an initial diagnosis. One of the common causes of incorrect operation of the refrigerator is the failure of the Checking this element does not require deep engineering knowledge, but requires the presence of a basic tool - a multimeter. Timely identification of a malfunctiontemperature sensor, which controls the on and off modes of the compressor.
Checking this element does not require deep engineering knowledge, but requires the presence of a basic tool - a multimeter. Timely detection of faults thermistor will allow you to avoid more serious problems with the control system. In this article, we will analyze in detail the algorithm of actions that will help you independently determine the state of the sensor.
Understanding the principle of operation of the sensor is necessary for the correct interpretation of the received readings. Thermistor changes its electrical resistance depending on the ambient temperature. If this parameter is outside the normal range, the electronic module receives incorrect signals, which leads to constant frost or, conversely, to a complete stop of cooling.
Principle of operation and types of temperature sensors
Modern refrigerators, be it Indesit, Bosch or LG, equipped with an electronic control system. They are based on sensors, most often negative temperature coefficient (NTC) thermistors. This means that as the temperature decreases, their resistance increases, and when heated, it decreases.
Depending on the design, sensors can be located in different areas: on the evaporator, in the air duct or directly in the storage chamber. Fault any of them can have different effects on the operation of the unit. For example, the defrost sensor is responsible for starting defrosting, and the main sensor regulates the cooling cycles.
It is important to understand that different models of refrigerators use thermistors with different nominal resistance values. The standard value is 10 kOhm at a temperature of +25°C, however, there are models with a resistance of 5 kOhm or 50 kOhm. Using an unsuitable analogue will lead to errors in the operation of the electronics.
For accurate diagnostics, you need to know not only the type of sensor, but also its location. In some models Samsung or Whirlpool access to the sensor may be difficult due to casing or a layer of ice, which requires partial disassembly of the unit before starting measurements.
Necessary tools and preparation for diagnostics
To carry out a high-quality test, you will need a minimum set of tools. The main device is digital multimeter, capable of measuring resistance in the range from tens of Ohms to hundreds of kOhms. It is desirable that the device has an audio test function to quickly check the continuity of the circuit.
In addition to the multimeter, you will need auxiliary tools to ensure safety and ease of operation. Before starting any manipulations with electrical components, it is necessary to turn off the power to the refrigerator by unplugging the plug from the socket.
- 🔧 Screwdrivers (Phillips and flathead) for removing protective panels.
- 🌡️ Cold source (ice pack) or hair dryer to change the temperature of the sensor.
- 📱 Smartphone with a camera for photographing the wiring diagram.
- ✂️ Insulating tape for insulating connections after checking.
⚠️ Attention: It is strictly forbidden to measure resistance on a sensor connected to the mains voltage. This will lead to instant failure of the multimmeter and may cause a short circuit.
Preparation of the workplace also plays an important role. Ensure good lighting in the repair area, as wires and connectors are often dark in color and difficult to see in the shadows. If the sensor is in a hard-to-reach place, you may need to move the refrigerator away from the wall.
Visual inspection and access to the sensor
The first stage of diagnosis is a visual inspection. In many cases, a fault can be detected without the use of measuring instruments. Carefully inspect the wires leading to the sensor for mechanical damage, kinks or traces of melted insulation.
Often the cause of a failure is oxidation of the contacts at the junction with the control board connector. If you notice a greenish coating or rust, the contacts must be cleaned. In some models Electrolux or Beko the connectors may be protected by rubber seals, which over time lose elasticity and allow moisture to pass through.
To access the sensor, you often need to remove the back wall inside the refrigerator or freezer. Be careful when removing plastic panels, as in the cold the plastic becomes brittle and breaks easily. It is recommended to first defrost the chamber for 15–20 minutes.
If a visual inspection does not reveal obvious defects, we proceed to an instrumental check. Before disconnecting the sensor, be sure to take a photo of the connection diagram so that during assembly you do not mix up the wires, especially if there are more than two of them.
Step-by-step instructions: how to check the sensor with a multimeter
The testing process involves measuring the resistance of the sensor at different temperatures. Switch the multimeter to resistance measurement mode (Ohms), selecting a limit of 20 kOhm or 200 kOhm, depending on the intended rating.
Disconnect the sensor connector from the control board or from the wiring harness. Touch the multimeter probes to the sensor contacts. Polarity in this case does not matter, since the thermistor is a non-polarized element.
Record the reading of the device. Now you need to check whether the resistance changes with temperature. To do this, you can hold the sensor in your hand (heat) or apply an ice pack to it (cool). The readings on the multimeter screen should change smoothly, without jumps.
☑️ Algorithm for checking the thermistor
If the resistance does not decrease when heated, and does not increase when cooled, the sensor is faulty. Also, a sign of a breakdown is the reading “1” or “OL” on the device screen, which indicates an open circuit, or “0,” which indicates a short circuit.
Analysis of readings and correspondence table
For correct interpretation of measurement results, it is necessary to compare the obtained data with reference values. Since ratings may vary, the table below is for the most common type of sensor with a resistance of 10 kOhm at +25°C.
| Temperature, °C | Resistance, kOhm (nominal) | Acceptable range, kOhm | Status |
|---|---|---|---|
| +25 | 10.0 | 9.5 – 10.5 | Normal |
| +10 | 16.5 | 15.5 – 17.5 | Normal |
| 0 | 26.0 | 24.0 – 28.0 | Normal |
| -10 | 40.0 | 38.0 – 42.0 | Normal |
| -20 | 60.0 | 57.0 – 63.0 | Normal |
If your readings differ significantly from the table ones, for example, at room temperature the device shows 2 kOhm or 500 kOhm, which means it has degraded. Such values will lead to the fact that the refrigerator will not work correctly: it will either not turn off or will not start at all. thermistor degraded. Such values will lead to the fact that the refrigerator will not work correctly: it will either not turn off or will not start at all.
It is important to take into account the error of the measuring device. Cheap multimeters can produce errors of up to 5–10%. For a more accurate diagnosis, you can use the comparison method: measure the resistance of a known good sensor of the same model and compare it with the one being tested.
Why can the readings “float”?
If the readings on the multimeter jump when the wire is slightly moved, this indicates a poor contact inside the sensor itself or at the place where the wires are soldered. Such a defect often manifests itself intermittently (periodically), which makes it difficult to diagnose without warming up or cooling the element.
Typical errors and signs of system malfunction
Incorrect operation of the temperature sensor is often disguised as other malfunctions. For example, if the refrigerator Atlant or Stinol started to freeze too much, turning food into ice, this may indicate that the sensor is “stuck” in a state of high resistance.
The control module “thinks” that the chamber is warm and does not turn off the compressor. In the opposite situation, when the resistance is too low, the unit may not turn on at all, believing that the required temperature has already been reached.
- ❄️ Freezing of a “cap” of ice on the back wall when the fan is running.
- 🔊 Frequent turning on and off of the compressor (clocking).
- 💡 The emergency temperature indicator on the control panel is on.
- 🌡️ The difference between the actual temperature in the chamber and the readings on the display.
Sometimes the problem lies not in the sensor itself, but in the wiring. Wires may rub against the housing or be damaged by rodents. Be sure to test the circuit from the sensor connector to the control board for a break.
Replacement of the sensor and final check
If the diagnostics confirmed a malfunction, the sensor must be replaced. When purchasing a new element, pay attention not only to the resistance, but also to the length of the wires and the type of connector. Universal sensors often require soldering or the use of adapters.
Install the new thermistor in place of the old one, making sure it fits snugly to the surface being measured. In some models, the sensor is inserted into a special socket on the evaporator and fixed with sealant or a latch.
⚠️ Attention: Do not use ordinary office tape or electrical tape to fix the sensor if they are not designed for low temperatures. Over time, the glue will dry and the sensor will no longer correctly read the evaporator temperature.
After replacement, reassemble the refrigerator in the reverse order. Plug in the unit and let it run for several hours. Check whether it has reached operating mode and whether the temperature in the chambers corresponds to the set values.
It is worth noting that the technical characteristics of some refrigerator models may vary slightly depending on the year of manufacture and region of assembly. If you doubt the compatibility of a part, it is better to check the manufacturer's official documentation or consult a service center.
Is it possible to temporarily short-circuit the sensor to make the refrigerator work?
Technically, this is possible for some models, where the short circuit simulates an emergency temperature, forcing the compressor to work constantly. However, this is extremely risky: the refrigerator will not turn off, which will lead to freezing of the evaporator, breakdown of the compressor and spoilage of food. This solution is only valid for a few hours to save the products before the technician arrives.
Why does the multimeter show different values for the same sensor?
This may be due to poor contact of the probes with the sensor terminals, a low battery in the multimeter, or the presence of carbon deposits on the contacts. It is also worth considering that the sensor has thermal inertia: it takes time to stabilize the readings after a temperature change (from 30 seconds to 2 minutes).
Where can I find the exact resistance table for my refrigerator model?
The exact data (Service Manual) is usually available in the technical documentation for service centers. They can be found in the public domain on specialized forums for repairing household appliances by searching for the model of the control board or the part code of the sensor.
Does the length of the wires of the new sensor affect the operation of the refrigerator?
For NTC thermistors, extending the wires of standard length (up to 1-2 meters) practically does not affect the readings, since the resistance of the wire itself is negligible compared to the sensor resistance. The main thing is to properly insulate the joints to prevent moisture from entering.