A modern refrigerator is a complex unit where each component performs its own function, ensuring the safety of food. However, like any equipment, it is subject to wear and tear, and one of the most common causes of failure is the failure of the compressor to start. In most cases, the culprit of this problem is not the motor itself, but a small but critical component - start-protective relay. It is responsible for starting the engine and protecting its windings from overloads.
Understanding the operating principle of this element will allow you to independently carry out initial diagnostics and even replace the part without calling a technician. Induction or posistor the type of device has its own characteristics that must be taken into account during repairs. If you notice that the refrigerator hums, but does not start, or turns on and turns off immediately, the problem most likely lies in the electrical start circuit.
In this article we will look in detail at how exactly this mechanism functions, why it fails and how choose the right replacement. Knowing the design of your unit, be it Indesit, Atlant or LG, will help save budget and time. It is important to approach the repair of the refrigerator carefully, observing safety precautions when working with electrical appliances.
The main purpose and functions of the relay in the refrigerator
The main task of the starting relay is to briefly supply voltage to the starting winding of the compressor motor. When the refrigerator is turned on, the motor rotor is motionless, and to spin it up requires significantly more force than to maintain rotation. Starting winding creates the necessary torque, after which it must be turned off, since constant work on it will lead to overheating and combustion of the motor.
Second, no less important function is thermal protection. The relay design has a built-in bimetallic element, which responds to the strength of the current flowing through the working winding. If the compressor seizes or another mechanical problem occurs, the current increases sharply. The bimetallic plate heats up, bends and opens the electrical circuit, preventing fire of the windings and destruction of the motor.
⚠️ Attention: Operating a refrigerator with a faulty thermal relay can lead to complete combustion of the compressor, the replacement of which is not economically feasible. At the first signs of incorrect operation (frequent clicks, heating of the motor housing), disconnect the device from the mains.
Thus, this small unit does double duty: it provides the correct starting algorithm and acts as a fuse. Without it, the safe operation of any piston compressor is impossible. Modern models may have an integrated protection system, but the classic circuit with an external relay remains the standard in the industry.
Operation principle: induction and posistor devices
There are two main types of starting devices on the household appliances market, and the principle of their operation differs significantly. Understanding this difference is necessary for correct diagnosis. Older models of refrigerators, as well as many budget options, are equipped with induction (electromagnetic) relays. They are based on a coil through which the current of the working winding passes.
When voltage is applied, the current is high, the magnetic field of the coil draws in the core, which mechanically closes the contacts of the starting winding. The engine begins to accelerate, the current drops, and the core, under the influence of gravity (or a spring), returns to its original position, opening the circuit. This process is accompanied by a characteristic click. Such relays are sensitive to the position of the refrigerator body.
More modern units, including many models Bosch and Samsunguse posistor (thermal) relays. There are no moving mechanical parts in their design. The key element here is posistor a ceramic element, the resistance of which increases sharply when heated. In a cold state, it passes current to the starting winding, heats up, the resistance increases, and the current practically stops.
Posistor devices are considered more reliable, since there is nothing mechanically stuck in them, but they are also susceptible to aging and can crack from vibration. After turning off the power, the posistor needs time (usually about a minute) to cool down before it can again pass current to start. That is why, when turned on again, the refrigerator often waits for a pause before starting the motor.
Typical signs of a malfunction of the starting mechanism
Diagnostics begins with observing the behavior of the refrigerator. The most striking symptom is the characteristic sound. The compressor tries to start, there is a loud click, a buzzing sound, and after a few seconds there is another shutdown click. The motor may be hot, but the shaft does not rotate.
Sometimes the refrigerator may operate unstably. It turns on, cools the chamber, but after a while it turns off prematurely or, conversely, it works without interruptions, without reaching the desired temperature. This may indicate that thermal protection it triggers falsely due to a violation of the calibration of the bimetallic plate.
Visual inspection can also provide a lot of information. If, when removing the relay, you see traces of burning, melted plastic, or smell burnt insulation, the part definitely requires replacement. Also, there should be no oxides or black deposits on the contacts inside the device.
- 🔊 The compressor hums for 3-5 seconds and clicks, but does not start - a classic sign of jammed contacts or a breakdown of the trigger mechanism.
- 🔥 The compressor motor housing becomes dangerously hot to the touch in the first minutes of operation - an activation signal thermal protection.
- 🧊 The refrigerator turns on only after a long period of inactivity (more than 5-10 minutes) - typical for an overheated posistor that does not have time to cool down.
- ⚡ Triggering of circuit breakers in the apartment's electrical panel when you try to turn on the refrigerator is a sign of a short circuit inside the relay or windings.
Dismantling and external inspection of the component
Before starting repairs, it is necessary to turn off the power to the refrigerator. Remove the rear panel at the bottom of the unit to gain access to the compressor. The start relay is usually placed on the side terminal of the compressor and secured with a bracket or plastic latches. Carefully disconnect the wires by first photographing their location or marking them with a marker.
Having removed the device, carefully inspect its body. It should be marked with technical specifications such as engine power and refrigerant type. Make sure there are no cracks in the case. For induction relays, it is important to check whether the core inside the coil is stuck. It should move freely under the influence of gravity when rocking.
☑️ Diagnostics of the refrigerator relay
If an external check does not reveal obvious defects, you will need a multimeter. Switch the device to resistance measurement mode (Ohms). Ring the contacts of the working and starting windings through the relay. In a normal state (cold for posistors), the circuit should ring. If the device shows infinity (one on the screen) where there should be a zero or a value close to it, then a break has occurred.
Table of main parameters and compatibility
When selecting a replacement, it is critical to take into account the parameters of the original device. Installing the wrong relay may result in the engine not starting or the starting winding burning out. Below is a table of correspondence between relay types and their characteristics for various compressors.
| Compressor type | Power (W) | Relay type | Characteristic cut-off current | Installation features |
|---|---|---|---|---|
| Low temperature (R12/R600a) | 1/8 - 1/6 HP | Posistor (PTC) | 1.3 - 1.6 A | Put on 3 pins |
| Medium temperature (R134a) | 1/5 - 1/4 HP | Induction | Depends on the weight of the core | Requires vertical installations |
| High-performance | 1/3 HP and higher | Posistor + Thermal | 2.0 - 2.5 A | Combined housing |
| Inverter (rarely) | Varies | Electronic unit | Controlled by a board | Cannot be easily repaired |
Please note that for compressors Atlant and Indesit universal posistor relays are often used, which are suitable for a wide range of powers. However, for old Soviet refrigerators or specific models Liebherr an original part with a specific cut-off current may be required. Markings on the case, such as RT, RCT or PTC, will help identify the type.
Is it possible to use a relay from another model?
Yes, you can, but only if two conditions are met: the type matches (inductive/posistor) and the nominal value matches current If you install a relay with a lower cut-off current, it will knock out during operation. If it is large, the motor winding will burn out when starting. In extreme cases, a difference in current of no more than 0.2 Amperes is allowed.
Replacement of parts and adjustment nuances
The replacement process does not require any special tools other than a screwdriver and pliers. The main thing is to correctly install the new relay on the contact group of the compressor. It should fit tightly, without backlash. If an induction relay is used, make sure that the arrow or inscription UP points straight up. Violation of the orientation will ensure that the core does not fall under its own weight and does not open the starting circuit.
For posistor devices, the orientation is less critical, but it is important to connect the wires to the terminals correctly. Color coding is usually used, but it is better to double-check the diagram in the instructions or on the body of the old relay. After installation, secure the device with a bracket or latches so that vibration during compressor operation does not break the contact.
⚠️ Attention: Before turning on for the first time after replacement, let the refrigerator stand in the off state for at least 15-20 minutes. This is necessary so that the refrigerant in the system calms down, and the new posistor (if installed) is guaranteed to cool down and be ready for operation.
Plug in the device. In the first seconds you can hear a more confident startup hum. If the compressor started working smoothly, without jerking or repeated clicks, and after a while cold appeared in the chambers, the repair can be considered successful. Check the current consumption with an ammeter: it must correspond to the rating indicated on the compressor nameplate.