A refrigerator is a complex electromechanical device where each element plays a critical role in maintaining low temperatures. When the compressor stops starting or hums but does not turn on, most often the problem lies in the start protection relay. This small component is responsible for supplying voltage to the motor windings and protecting against overloads.
Owners often confuse the concepts of adjustment and replacement, believing that the device can be “tweaked” or calibrated. In fact, in 95% of cases, an exact replacement of the burnt out element with a working analogue is required. However, before this, it is necessary to carry out proper diagnostics to make sure that the reason is in the relay, and not in the compressor itself or the wiring.
In this guide, we will analyze the physical principles of the device, testing methods with a multimeter, and a step-by-step algorithm for replacement. You will learn how to distinguish a thermal relay from a starting one, and you will understand why contact group it can stick. The correct approach to repair will save on calling a technician and extend the life of the equipment.
Principle of operation and types of start-up protection devices
The start-up protection relay is an electromagnetic or thermal switch that controls the start of the compressor motor. When the refrigerator is turned on, the current consumed by the motor increases sharply, and the relay closes the starting winding circuit. As soon as the rotor picks up speed, the current drops and the device opens the circuit, leaving only the main winding to work.
There are two main types of such devices: induction (electromagnetic) and posistor. Induction relays use a coil with a movable core, which retracts at high current and closes the contacts. PTC models, more modern, use the property of a semiconductor to change resistance when heated. The PTC after cooling (usually 3-5 minutes) restores conductivity, which explains the delay before restarting the compressor.
Thermal protection is built into the housing or located nearby and reacts to a critical increase in temperature or current. If the compressor overheats, the bimetallic strip opens the circuit, preventing the windings from burning out. Understanding exactly which one switching mechanism is used in your model is important for correct diagnosis.
- 🔌 Electromagnetic relays is a classic version, often found in older models Atlant or ZIL, position sensitive housings.
- 🌡️ Posistor starters —more reliable, have no moving parts, widely used in modern refrigerators Indesit i Beko.
- ⚡ Combined devices - combine the starting function and thermal protection in one housing, which simplifies installation, but requires precise selection.
⚠️ Attention: An attempt to “disassemble” and clean the contacts inside sealed housing of a posistor relay almost always leads to final failure. These elements are designed for one-time use and replacement as an assembly.
Fault diagnosis: signs and testing methods
Before proceeding with replacement, you need to make sure that the relay has actually failed. Typical signs of a malfunction are clicks when trying to start, the absence of a hum from the compressor, or, conversely, a hum followed by shutting down after a few seconds. Sometimes you may notice a burning smell or melted plastic in the connection area.
For an accurate check, you will need a multimeter. First, the device must be removed from the power supply. A visual inspection may reveal cracks in the case or blackening of the contacts, which is already sufficient reason for replacement. If there are no external defects, we proceed to the continuity test of the circuit.
The posistor is checked by measuring the resistance: in a cold state it should be low (several tens of Ohms), and when heated it should tend to infinity. For electromagnetic relays, the integrity of the coil and the mobility of the core are checked. If the coil rings and the core is jammed, the device will not work correctly.
It is also important to check the condition of the wiring going to the terminals. Often, oxidation or burning of wires creates a false impression that the relay itself is broken. Contact group must be clean and free of carbon deposits. If the wires are melted, they must be cleaned or replaced before installing a new element.
Preparation for replacement: tools and safety
Repairing electrical appliances requires compliance with strict safety rules. The very first action before starting any work is to completely disconnect the refrigerator from the electrical network. Even briefly touching live parts can lead to serious injury.
For work you will need a minimum set of tools: flat-head and Phillips screwdrivers, side cutters (nippers), pliers and a multimeter. It is also recommended to prepare electrical tape or heat shrink to insulate the connections. It is a good idea to have a flashlight on hand, as the back of the compressor is often poorly lit.
☑️ Safety check before repair
Access to the relay is usually located at the bottom of the refrigerator, at the back. In some models, for example Liebherr or Siemens, you may need to remove the protective metal or plastic casing secured with latches or screws. Be careful when removing the casing so as not to damage the condenser tubes.
Step-by-step instructions for dismantling and installation
The replacement process begins by removing the old relay. It simply slides onto the three pins coming out of the compressor. Gently rock the device from side to side to remove it. Do not use excessive force to avoid breaking the ceramic insulator or tearing off the wires.
Pay attention to the orientation of the device: the housing usually has an "UP" (up) marking or an arrow indicating the correct position. This is critical for electromagnetic relays since the core must move vertically under the influence of gravity. Incorrect installation will result in the compressor not starting.
If the new relay has a different connector type or wire length, they can be carefully cut and connected through a terminal block or twisted and then soldered. The main thing is to ensure reliable contact and high-quality insulation. Use heat-shrink tubing to protect against moisture and vibration.
What to do if the new relay does not fit the connector?
If the connectors are different, you can carefully transfer the contact pads from the old relay to the new one, observing the polarity. However, this requires soldering skills. A safer option is to use adapter blocks, if they are included, or replace the relay with an original one for your compressor model.
After installation, reassemble the structure in the reverse order. Make sure that the relay fits tightly on the compressor contacts and is secured with a metal bracket or plastic holder, if provided by the design. Only after visually checking all connections can you turn on the refrigerator to the network.
Compatibility table and relay markings
When selecting a new element, it is important to take into account not only the brand of the refrigerator, but also the model of the compressor. Different manufacturers use different labeling standards. Below is a table of correspondence between popular series of relays and compressors.
| Refrigerator manufacturer | Compressor type | Relay marking (example) | Device type |
|---|---|---|---|
| Atlant, ZIL | KT-60, SK-100 | RT-S, R-1 | Induction |
| Indesit, Ariston | Aspera, Danfoss | 103N0021, 3161334 | Posistor |
| Beko, Candy | Embraco, Secop | 6350102, 8160602 | Pozistor |
| LG, Samsung | LG, Samsung (inverter) | Model specific | Electronic unit |
Please note that for inverter compressors the concept of “starting relay” in its classical form is not applicable. It uses a complex electronic control board that regulates the engine speed. Replacement of the relay in inverter systems this is not possible - diagnostics and repair of the board or replacement of the compressor assembly is required.
⚠️ Attention: Technical characteristics of compressors and compatible articles spare parts may be changed by manufacturers. Before purchasing, be sure to check the part number on the housing of your old relay or compressor with the supplier's catalog.
Frequent errors and possible complications
One of the most common mistakes is installing a relay of inappropriate power. If the device is designed for less starting current, it will constantly turn off the compressor or burn itself out. If it is larger, the starting winding may not open, which will lead to overheating and combustion of the engine.
The condition of the capacitor is also often ignored if it is in the circuit. In some circuits, a capacitor is connected in parallel with the starting winding, which helps to shift the phase of the current. If it is swollen or has lost capacity, even a new relay will not help start the engine. Check the capacitor for swelling and electrolyte leakage.
Another problem is vibration. If the relay is poorly secured, vibration from the operating compressor may cause contact rattling or false thermal protection activation. Make sure that the retaining frame or spring is installed correctly and tightly presses the device to the compressor body.
When professional help is required
Despite the apparent simplicity, There are situations where DIY repairs may be dangerous or impractical. If after replacing the relay the compressor hums, but the shaft does not turn, the motor itself may be jammed. Attempts to “unwedge” it with a hammer or stick often lead to depressurization of the housing and leakage of freon.
It is also worth contacting a specialist if you find that the compressor windings are “ringing” on the housing (insulation breakdown). This means that the electric motor is faulty, and its replacement requires evacuation of the system and charging with refrigerant, which cannot be done at home without special equipment.
If the refrigerator is under warranty, any independent repair will lead to loss of warranty. In this case, it is better to call an authorized specialist, even if the problem seems trivial. Keep receipts and documents for the equipment.
Is it possible to use a relay from another refrigerator model?
The use of analogues is only possible if the electrical characteristics are completely identical: coil voltage, operating current and connection type. Visual similarity does not guarantee correct operation. It is better to look for the original article or a verified cross-number.
Why does the relay heat up during operation?
A slight heating of the case up to 60-70 degrees may be the norm for thermal relays. However, if the device heats up to a temperature at which it is impossible to touch, this is a sign of a malfunction: poor contact, excessive current, or incorrect installation.
How often should the starting relay be changed?
The service life of a high-quality relay is 10-15 years. Frequent replacements (once a year) indicate a problem with the compressor itself (turn-to-turn short circuit) or unstable voltage in the network. In the latter case, it is recommended to install a stabilizer.
Does the room temperature affect the operation of the relay?
Yes, it does. At very low temperatures (below +10°C), the viscosity of the oil in the compressor increases, the starting current increases, and the relay may not be able to start. At high temperatures (>+35°C), thermal protection may operate prematurely.
What to do if there is no original relay?
You can choose a universal analogue. There are sets of universal starting relays with a set of adapters for different types of compressors. The main thing is to correctly determine the compressor power (indicated on the nameplate) and select the appropriate range.