Modern refrigerators Bosch are equipped with a complex electronic control system that automatically regulates the temperature in the chambers, controls defrosting and controls the operation of the compressor. Temperature sensors play here the role of the “eye” of the system, transmitting information to the control module about the real state inside the chambers. If one of the sensors fails or begins to transmit distorted data, the refrigerator stops working correctly: food can spoil, ice coats freeze, and the unit hums continuously.
Self-diagnosis allows you to save a significant amount on calling a technician, since often the problem lies precisely in a banal open circuit or oxidation of contacts. In this article we will look at how to correctly check the sensorwhat tools are needed for this and how to interpret the obtained resistance values.
It is important to understand that electronics Bosch are very sensitive to voltage drops, so before starting any work it is necessary to completely de-energize device. The accuracy of the measurements is a critically important point: the error of the multimeter can lead to an erroneous conclusion about the serviceability of the part, which will entail unnecessary costs for the purchase of new spare parts. Let's look at the diagnostic process step by step.
The principle of operation and types of sensors in Bosch technology
In refrigeration equipment of the German brand, NTC thermistors (Negative Temperature Coefficient) are most often used. Their physical feature is that when the temperature rises, their electrical resistance drops, and when cooled, it increases. This is a non-linear relationship, which is strictly controlled by the manufacturer for each series of refrigerators.
The system can include several independent sensors: one controls the air in the refrigerator compartment, the second in the freezer, the third can monitor the evaporator temperature to control defrost. Control module reads the readings every few seconds and makes a decision to turn the compressor on or off.
If the sensor “lies”, the refrigerator may think that it is warm inside and work without stopping, or assume that the cold has already been reached and not turn on at all. Here are the main signs of a malfunction that you should pay attention to:
- 🌡️ Condensation forms on the walls of the chambers or ice freezes where it should not be.
- ❄️ Products in the refrigerator freeze, although the regulator is at a minimum.
- 🔊 The compressor is working cyclically incorrect: either for too long or at too short intervals.
- 💡 An alarm indication lights up on the display or the temperature icon flashes.
Understanding which one has failed is often suggested by the very logic of the unit’s operation. For example, if defrosting does not start, the problem is almost certainly in the evaporator sensor, and not in the main air sensor. thermistor has failed, the very logic of the unit’s operation often suggests. For example, if defrost does not start, the problem is almost certainly with the evaporator sensor and not the main air sensor.
Necessary tools and preparation for diagnostics
For a quality check, you will need a minimum set of tools that most home craftsmen can find. The main requirement is the accuracy of the measuring instruments. A regular indicator screwdriver will not help here; you need just one digital multimeter (tester) with the ability to measure resistance in the range from 1 kOhm to 50 kOhm.
Before you start disassembling the refrigerator, you need to prepare a workplace. Cover the floor with soft material to avoid scratching the coating and damaging fragile plastic elements when dismantling them. Also stock up on capacious dishes to collect water if ice has accumulated in the freezer.
☑️ Diagnostic tools
Don't forget about safety. Although the voltage in the sensors is low, the refrigerator itself is connected to a 220V network. Therefore, the first rule is complete shutdown from the power supply before removing any panels and plastic casings.
Removal and access to temperature sensors
Access to the sensor in the refrigerator compartment is usually hidden behind a plastic panel on the back wall or in the side parts. In models Bosch with a system No Frost the sensor is often built into the air duct or mounted on the evaporator. To get to it, you will have to remove shelves, drawers and decorative trims.
Be careful with plastic latches - they are quite strong in German technology, but at low temperatures they become brittle. If the plastic does not give in, do not use brute force, it is better to slightly warm the mounting area with a hairdryer or let it warm up at room temperature.
⚠️ Attention: When removing the back panel, ice may sprinkle in the freezer. Do not try to break it off with a knife or sharp objects - there is a high risk of damaging the circuit tubes or sensor wiring. Use only warm water or a hairdryer.
The sensor itself is a small plastic or metal cylinder from which two wires go deep into the case to the electronic unit. Often it is simply inserted into the technological hole and secured with sealant or a clip.
To remove the sensor, sometimes it is necessary to carefully cut off the old sealant. The main thing is not to damage the insulation of the wires going to the connector. If the wires are intertwined with other harnesses, carefully release them so that you can disconnect the chip.
Method of checking with a multimeter: step-by-step instructions
The most reliable diagnostic method is measurement electrical resistance. To do this, switch the multimeter to resistance measurement mode (Ω icon) and select the limit of 20 kOhm or 200 kOhm, depending on the model of your tester. Connect the probes to the sensor contacts (polarity is not important for thermistors).
Record the readings at room temperature. Then place the sensor in a container with warm water (not boiling water, 40-50°C is enough) and watch the numbers on the screen change. The resistance should gradually decrease. After this, you can check the reaction to cold by placing the sensor in the freezer - the numbers should increase.
If the multimeter shows “1” (infinity) or “0” (short circuit) regardless of temperature, the sensor is clearly faulty. Also an alarming signal is a sharp jump in readings or lack of response to changes in ambient temperature.
Below is a table with approximate resistance values for the most common thermistors used in refrigerators Bosch. Please note that the values may vary slightly depending on the specific series.
| Air temperature (°C) | Resistance (kOhm) - Type A | Resistance (kOhm) - Type B | Status |
|---|---|---|---|
| +25°C | ~6.0 - 6.5 | ~10.0 - 11.0 | Normal |
| +10°C | ~9.0 - 10.0 | ~16.0 - 18.0 | Normal |
| 0°C | ~12.0 - 13.0 | ~22.0 - 24.0 | Normal |
| -18°C | ~30.0 - 35.0 | ~55.0 - 60.0 | Normal |
Compare your measurements with the tabular data. If the deviations are more than 20-30%, the part requires replacement, since the electronics will receive incorrect data.
Diagnostics through error codes on the display
Many models Bosch are equipped with a digital display that displays fault codes. This makes it much easier to find the problem by pointing directly to the area where the sensor is not behaving correctly. Usually the Error code is accompanied by a flashing temperature indicator.
The most common codes associated with temperature sensors:
- 🔢 E1 — Malfunction of the temperature sensor in the refrigerator compartment (break or short circuit).
- 🔢 E2 — Problem with the sensor in the freezer compartment.
- 🔢 E3 — Malfunction of the evaporator defrost sensor.
- 🔢 F4 — Communication error between the control module and sensors.
However, the codes may vary depending on the generation of the refrigerator. To accurately decipher the error, look at the user manual or find a technical sticker inside the case (often on the end of the door or on the back wall).
What to do if the error code does not reset?
If after replacing the sensor the code continues to light, try completely turning off the power to the refrigerator for 15-20 minutes. The electronic unit should reboot and take new readings. If the error returns instantly, check the integrity of the wiring to the control board.
Sometimes the error can be caused not by a breakdown of the sensor itself, but by oxidation of the contacts in the connector or damage to the wire in the door hinge. Carefully inspect the entire circuit from the sensor to the board.
Replacement of the faulty element and calibration
If diagnostics confirm a malfunction, you must purchase an original spare part or a high-quality analogue with identical characteristics. When purchasing, pay attention to the markings and appearance of the connector. Installation This is done in the reverse order of dismantling.
Carefully insert the new sensor into the seat. If the design includes thermally conductive adhesive or sealant, be sure to use it - this will ensure proper heat transfer and protection from moisture. Without sealing, condensation may get inside, which will lead to a new breakdown in a short time.
⚠️ Attention: Do not use ordinary office glue or tape to fix the sensor. They do not have the required thermal conductivity, and temperature readings will arrive with a delay, which will disrupt the compressor operation algorithm.
After connecting the wires and assembling the plastic panels, turn on the refrigerator. During the first hours of operation, the device can work in enhanced mode, gaining temperature. Do not load products into the chambers until the temperature has stabilized (usually 2-4 hours).
Frequent questions and problems during testing
Owners often encounter a situation where a seemingly working sensor causes malfunctions. This may be due to the “drift” of characteristics: the sensor works, but its readings gradually shift from real values. In this case, only replacement helps.
It is also important to consider that in two-compressor models Bosch the sensors may be different for each chamber. They cannot be confused, as they may have different cable lengths or calibration curves.
If you are not confident in your abilities or the multimeter shows strange results, it is better to contact a specialized service. Refrigerator electronics are complex, and an error in diagnostics can lead to failure of an expensive control module.
Is it possible to check the sensor without a multimeter?
It is impossible to accurately determine serviceability without instruments. However, an indirect sign can be the operation of the compressor: if it does not turn on when the chamber is clearly overheated, and does not turn off during defrosting, there is a high probability of a problem with the sensor. But these are just guesses that require confirmation with a tool.
Where to buy an original sensor for Bosch?
It is better to look for original spare parts in authorized service centers or specialized stores of spare parts for household appliances, indicating the exact model number (E-Nr) of your refrigerator. There are many analogues on the market, but their parameters may differ.
Why does the refrigerator not turn off for a long time after replacing the sensor?
This is a normal phenomenon when first started. The unit needs time to cool the entire volume of the chambers and stabilize the temperature. If after 5-6 hours of continuous operation the temperature does not reach the set values, then it is worth checking the tightness of the system and the amount of refrigerant.
Does humidity affect the sensor readings?
Yes, if the tightness of the sensor housing or its installation location is broken, moisture can cause oxidation of the contacts or a short circuit, which will lead to incorrect resistance readings and errors in the operation of electronics.