A sudden stop of the compressor or characteristic clicks when trying to start the refrigerator Bosch often indicates a failure of the start-up protection device. This small but critical relay is responsible for supplying voltage to the motor windings and protecting it from overloads. When this component stops functioning, the refrigerator stops cooling and food begins to spoil. In most cases, replacing this part is the only way to restore the operation of the unit without calling a technician.
The procedure for dismantling the relay on models Bosch is not technically difficult, but requires compliance with safety measures and an understanding of the unit's structure. Incorrect operation may damage the compressor or electrical circuit. In this article we will look in detail at how to safely remove a faulty element, carry out a visual diagnosis of it and prepare a place for installing a new part.
Before you start disassembling, you need to make sure that the problem lies in the relay, and not in the compressor itself or the wiring. Often the symptoms are similar: the motor hums, but does not start, or makes a loud click and goes silent. The working relay in a cold state should show resistance between contacts 1 and 3 within 3-15 Ohms, as well as a characteristic sound rolling ball when shaken. If the sound of broken glass or ceramics is heard inside, replacement is inevitable.
Fault diagnosis and signs of breakdown
The first sign that starting relay has failed is the unnatural behavior of the compressor. Instead of the steady hum of a running motor, you may hear a series of rapid clicks repeated every few seconds. This means that the relay is trying to start the engine, but due to internal damage to the contacts or a broken winding, it opens the circuit. In some cases, the compressor may hum for several seconds, become very hot and then turn off by a thermal release.
For an accurate diagnosis, it is necessary to carry out an external inspection and “listening”. Remove the back panel of the refrigerator Bosch and locate the black cylindrical or cubic compressor. The relay is usually mounted on the side of its shaft. Gently tap the relay housing with the handle of a screwdriver. If a ringing sound is heard inside, reminiscent of the sound of broken glass, it means thermistor or the ceramic element inside is destroyed. This is a common problem for PTC type relays.
It is also worth paying attention to the condition of the contacts. If the relay is removable, you can carefully disconnect it (after turning off the power to the refrigerator!) and shake it. The absence of the sound of a rolling ball in a relay with a posistor indicates that the mechanism is stuck or destroyed. In models with an electromagnetic relay, the cause may be burning of the contacts, which can be seen by black carbon deposits when opening the case.
⚠️ Attention: Before any intervention in the electrical part of the refrigerator Bosch be sure to disconnect it from the network. Residual voltage or accidental contact with live parts under load can result in serious electrical injury.
Necessary tools and workplace preparation
To successfully complete the replacement task relay you do not need a complex professional tool. However, using the wrong items may complicate the process or damage the plastic latches of the relay housing. Preparation of the workplace also plays an important role: ensure that the area near the compressor is well lit, as it is often dark and cramped there.
You will need the following tools:
- 🔧 Pliers or pliers with narrow jaws for gripping the terminals.
- 🪛 Screwdriver (slotted and Phillips) for removing protective panels and covers.
- 🧤 Dielectric gloves to protect hands when working with electrical equipment.
- 📸 Smartphone for photographing the wiring diagram before removal.
- 🧹 Soft brush to clean the compressor contacts from dust and oxides.
Pay special attention to the cleanliness of the contacts on the compressor itself. Before installing a new relay, it is recommended to carefully clean the compressor pins with fine sandpaper or a file if an oxide film is visible on them. Dirty contacts can cause the new relay to fail again or cause poor contact, leading to heating and melting of the plastic.
If your refrigerator Bosch has access to the diagnostic menu through the control panel, it is worth checking the error codes before starting work. For example, an error E09 or F09 on some models may indicate problems with starting the compressor, which indirectly confirms the need to check the starting circuit. However, mechanical testing of the relay always takes precedence when there are obvious physical signs of failure.
Step-by-step instructions: how to remove a relay
The process of removing relays on refrigerators Bosch is standardized, but may have slight nuances depending on the series (for example, Classixx, KGN, GSN). The main rule is not to use excessive force. Plastic, especially on old refrigerators, becomes brittle and can crack from a careless tug.
Follow the steps in the following sequence:
- Disconnect the refrigerator from the power supply and move it away from the wall, providing access to the back wall.
- Remove the bottom protective panel (if there is one) or bend it to gain access to the compressor.
- Find the start relay: it is placed on the side terminal of the compressor and is often covered with a plastic casing.
- Carefully remove the casing by snapping the latches or unscrewing the screws.
- Take a photo of the connection of the wires to relay terminals.
- Remove the relay from the compressor terminals. It is usually held in place by a tight fit and a retaining bracket.
- Disconnect the wires from the relay terminals using pliers so as not to damage the insulation.
☑️ Checklist before removing the relay
When removing the relay, pay attention to the fixing metal bracket. On many models Bosch the relay is held in place by a spring bar that wraps around the housing. To remove the relay, you need to carefully press this bar up or to the side, while simultaneously pulling the relay off the compressor contacts. Do not pull on the wires - this may cause them to break at the base.
⚠️ Attention: If the relay cannot be removed with a slight force, do not pull it sharply. Check if you forgot to remove the retaining bracket or plastic holder. Excessive force can break the plastic terminals on the compressor, the repair of which is extremely difficult.
Types of relays and their compatibility with Bosch models
In refrigerators Bosch mainly two types of starting ones are used devices: posistor (PTC) and induction (electromagnetic). Understanding the difference between them is important for the correct selection of spare parts. PTC relays are more modern, have no moving parts (except for a thermal release) and are considered more reliable, but are sensitive to shock.
Electromagnetic relays (often found in older models) operate on the principle of closing contacts at a certain current. They have a movable core and produce a louder clicking sound when operating. Replacing one type with another is possible only within the framework of special cross-analogs designed for interchangeability, since their electrical characteristics and connection diagrams differ.
Below is a table that helps to identify the type of relay by external features and markings:
| Characteristics | Posistor relay (PTC) | Electromagnetic relay | Thermal relay (protection) |
|---|---|---|---|
| Design | Plastic case, ceramic element inside | Metal or plastic case with coil | Bimetal plate, often in one housing with a starter |
| Sound when shaking | Ringing of a broken one (if faulty) or silence | Clear knock of a moving core | Unverifiable by shaking |
| Marking | Often contains letters PTC, 15-25 Ohm |
Indication of voltage and current, for example 220V |
Temperature range, for example 120°C |
| Failure frequency | High (fragility of ceramics) | Medium (burning of contacts) | Low (if the compressor is working) |
When buying a new relay for Bosch focus not only on the model of the refrigerator, but also on the parameters of the old relay. It is important that the posistor resistance and the rated current match. Using an unsuitable analogue may result in the compressor starting intermittently or not starting at all.
Is it possible to temporarily start a refrigerator without a relay?
Theoretically, you can start the compressor by applying voltage directly to the starting winding, but doing this is strictly not recommended without special knowledge. This may result in burnt compressor windings or fire due to lack of protection. Use this method only for short-term diagnostics by professionals.
Frequent errors during dismantling and installation
Even a simple operation to replace a relay can go wrong if you make typical beginner mistakes. One of the most common is ignoring the condition of the wires. If the insulation on the wires going to the relay is melted or cracked, installing a new relay will do nothing. The wires must be cleaned and, if necessary, extended using high-quality insulation.
Another mistake is incorrect placement of the relay on the compressor contacts. The compressor pins must fit into the relay sockets tightly and all the way. If the relay is not seated tightly, the contact will disappear when the compressor vibrates, causing sparking and heating. In some cases, it is necessary to carefully bend the contacts inside the relay connector with pliers to ensure a tight fit.
Thermal protection relay is also often forgotten. On many models Bosch the starting and thermal relays are combined into one unit or mounted together. When replacing one element, it is recommended to check the second one as well. If the thermal relay is “tired”, it can turn off a working compressor ahead of time, creating a false impression of problems with starting.
Do not forget about the orientation of the relay. Some models have a strictly defined installation position (for example, arrow UP up). Installing the relay upside down can disrupt the operation of the thermal release or lead to moisture and dust getting inside the housing.
Checking operation after replacement
Once the new relay is installed and all wires are connected according to the photograph taken earlier, you can proceed to testing. Don't rush to close the back panel right away. Leave access to the compressor open to control the initial start-up process. This will allow you to notice sparking or hear uncharacteristic sounds in time.
Plug in the refrigerator. In the first seconds you can hear a hum, which after 1-3 seconds should be replaced by the smooth sound of a running motor. If you hear a clicking sound and the motor stops talking, turn off the power immediately. This is a signal that the relay did not work, the compressor is faulty, or an error was made during installation.
Pay attention to the heating of the body of the new relay. It may become slightly warm during the first 10-15 minutes of operation, but should not be so hot that it is impossible to touch. Excessive heating indicates poor contact or mismatch of compressor power relay settings.
⚠️ Attention: If, after replacing the relay, the compressor continues to hum and does not start for more than 5 seconds, turn off the refrigerator. Long-term operation in the “humming” mode without rotating the shaft will lead to overheating and combustion of the compressor windings in a matter of minutes.
Questions and answers (FAQ)
Is it possible to repair an old relay if the inside is broken posistor?
Theoretically, you can try to find a posistor with the same resistance and replace it, but in practice this is impractical. The cost of a new relay for Bosch low is low, and the time spent searching for parts and soldering is not worth it. In addition, a broken housing seal can lead to moisture ingress.
Why does a new relay burn out a few days after replacement?
This may indicate a more serious problem with the compressor, for example, an interturn short circuit of the windings or jamming of the mechanism. In this case, the starting current exceeds the rated one, and the relay burns out, performing its protective function. Compressor diagnostics are required.
Where can you find the relay markings on a Bosch refrigerator?
The markings are usually applied to the side or top edge of the plastic relay housing. Look for codes like 38311, PTC-15 or logos of component manufacturers, such as Secop, Danfoss or Siemens.
Does tilting the refrigerator affect the operation of the relay?
Yes, especially for electromagnetic relays. If the refrigerator is placed at a strong angle, gravity may prevent the core or moving contacts from returning to their original position, which will lead to incorrect operation or sticking of the relay.
How often do you need to change the maintenance relay?
The relay does not have a set service life and is replaced only in the event of a malfunction. Preventive replacement is not required if the refrigerator is operating normally. The average service life of a high-quality relay is 5-10 years.