When the refrigerator suddenly stops freezing and the compressor does not make the usual hum, the culprit most often turns out to be small but critical detail - starting relay. This compact module, hidden next to the motor, is responsible for starting the compressor and protecting it from overloads. Without it, even a working engine will not be able to start working, and the refrigerator will turn into an expensive cabinet.
In this article we will look at how exactly starting relay controls the start of the compressor, what physical processes are behind this, and why its breakdown leads to characteristic symptoms - from complete silence of the equipment to cyclical clicks without cooling. You will also learn how to check the relay yourself with a multimeter, without resorting to the services of a technician, and when it can be repaired and when it can only be replaced.
What is a starting relay and why is it needed in the refrigerator
Starting relay (sometimes called start-protective) is an electromechanical or electronic device that performs two key functions:
- 🔌 Starting the compressor - supplies short-term current to the starting winding of the motor to overcome the inertia of the rotor.
- 🛡️ Overheat protection - turns off the power if the motor consumes too much current (for example, when jammed).
The fact is that the refrigerator compressor is an asynchronous electric motor with two windings: working and starting. The working winding keeps the rotor spinning, but its magnetic field is not enough to move it. This is where a relay is needed: it connects the starting winding for a split second, creating additional torque. As soon as the rotor spins to the desired speed (usually 1-2 seconds), the relay automatically opens the starting winding circuit.
Without this mechanism, the compressor will either not start at all, or will consume excessive current, risking burning out. This is especially true for refrigerators with inverter compressors, where the relay plays the role of not only a starting, but also a regulating device.
Design and principle of operation of the starting relay
The design of the relay depends on its type, but in the classic version (electromechanical) it consists of:
- 🧲 Coils — creates a magnetic field when current flows.
- 🔧 Anchors —a moving contact that closes/opens the circuit of the starting winding.
- 🔥 Bimetal plate —protects against overheating, breaking the circuit when excess current.
- 🔌 Contacts —connected to the windings of the compressor and the 220V network.
How it works step by step:
- When the refrigerator is turned on, the current enters the working winding of the compressor and the relay coil.
- The coil creates a magnetic field that attracts the armature, which closes the contacts of the starting winding.
- The compressor starts, the current in the working winding drops (the rotor has spun), the magnetic field weakens, and the armature returns to its original position, opening the starting winding.
- If the current exceeds the norm (for example, due to mechanical blocking), the bimetallic plate heats up and breaks the circuit, preventing overheating.
In modern refrigerators (for example, Samsung No Frost or LG Inverter Linear) often used electronic relays, where the role of the coil and armature is performed by a semiconductor switch (thyristor or transistor). Such relays are more compact, more reliable and more accurately control the start.
What is the difference between a starting relay and a thermal relay?
The thermal relay (or thermostat) is responsible for turning the compressor on/off depending on the temperature in the chamber. The starting relay works only when the engine starts and is not connected to temperature sensors.
Schemes for connecting the relay to the compressor
There are two main circuits for connecting the starting relay, which depend on the type of compressor:
| Type of compressor | Scheme connections | Features |
|---|---|---|
| Single-phase asynchronous | The relay is connected to the starting and operating windings in parallel | Used in 90% of household refrigerators (Atlant, Indesit, Biryusa) |
| Three-phase | The relay controls the phase connected to the starting winding | Rarely found in everyday life, more often in industrial installations |
| Inverter | Electronic relay integrated into the control board | No mechanical contacts, control via PWM signals |
There is usually a relay on the body contact marking:
S (Start) - starting winding,
R (Run) - working winding,
C (Common) - common contact.
In refrigerators Samsung or Bosch other designations may be used, so before replacing the relay be sure to check the diagram on the compressor or in the service manual.
Signs of a faulty start relay
Failure of the relay is manifested by clear symptoms that are difficult to confuse with other faults:
- 🔇 The compressor does not start —the refrigerator does not freeze, but the light inside is on. At the same time, clicks of the relay are heard. (Attempts to start), but the motor does not hum.
- ⚡ The compressor turns on and immediately turns off —the relay is activated for protection due to the false operation of the bimetallic plate.
- 🔥 The relay gets hot or smells like burning —a sign burnt contacts or a short circuit in the coil winding.
- 🔄 Cyclic clicks without starting —the relay tries to turn on the compressor, but it does not spin up (perhaps the winding is jammed or burned out).
Critical moment: if the relay clicks, but the compressor does not start within 1-2 seconds, this almost always indicates a malfunction of the relay or the motor starting winding. In rare cases, the problem may be an unstable network voltage (less than 190V or more than 240V), but this can be easily checked with a multimeter.
⚠️ Attention: If the relay makes repeated clicks at intervals of 5-10 seconds, do not try to start the compressor. manually (for example, due to a short circuit of the contacts). This can lead to an interturn short circuit in the motor windings!
How to check the starting relay with a multimeter
Diagnostics of the relay does not require professional equipment - just a digital multimeter and knowledge of electrical engineering. Follow this algorithm:
☑️ Checking the starting relay
Step 1. Checking the relay coil
Switch the multimeter to resistance measurement mode (200 Ohm) Connect the probes to the coil terminals (usually these are contacts S and C or R i C).A working coil should show resistance in the range 10–50 OhmIf the device shows OL (break) or 0 (short circuit), the relay is faulty.
Step 2. Checking the contacts
In the continuity mode, check the circuit between contacts S and R in two states:
- In the normal position (without voltage supply) - the circuit should be open (no sound signal).
- When the armature is forced to close (you can gently press it with a screwdriver) - the circuit should closed (beeping of the multimeter).
If the contacts do not close or, conversely, are always closed - the relay is subject to replacement.
Step 3. Visual inspection
Disassemble the relay (if it is collapsible) and inspect:
- Bimetallic plate for deformation.
- Contacts for carbon deposits or melting.
- Coil for overheating (darkening of the varnish on the wire).
If the contacts have a black coating or are melted, cleaning with sandpaper will give a temporary effect - it is better to replace the relay.⚠️ Attention: When checking the relay do not apply 220V to it directly without load (compressor). This can damage the bimetallic plate or coil!
Typical causes of relay failure and how to avoid them
The relay does not fail, but due to systematic violations use or normal wear and tear. Here are the main reasons:
- ⚡ Power surges — lead to breakdown of the coil or “sticking” of the contacts. Solution: use a voltage stabilizer for the refrigerator.
- 🔥 Overheating of the compressor - if the motor is worn out (for example, due to a freon leak or a clogged capillary), the relay operates too often and wears out. Solution: regularly clean the refrigerator condenser.
- 💧 Moisture ingress —condensation on the contacts causes corrosion and short circuits. Solution: monitor the tightness of the door seal.
- ⏳ Natural wear —the relay has a limited operating life (about 100,000 cycles). After 7–10 years of operation, it is recommended to replace it preventively.
In refrigerators with a system No Frost the relay wears out faster due to more frequent activation of the compressor (to defrost the evaporator). If your refrigerator is of this type, check the condition of the relay every 5-6 years.
Replacing the starting relay: step-by-step instructions
If diagnostics have confirmed that the relay is faulty, it must be replaced. This does not require special skills, but it is important to follow the sequence of actions:
Step 1. Preparation
Unplug the refrigerator and move it away from the wall to gain access to the compressor. It is located at the bottom of the back wall and looks like a black metal cylinder with tubes. The relay is attached directly to the compressor housing or next to it.
Step 2. Removing the old relay
Carefully remove the protective casing (if any) and disconnect the wires from the relay, having previously photographed their location. Usually the relay is attached to latches or screws - unscrew them and remove the device.
Step 3. Installing a new relay
Purchase a relay with the same parameters as the old one. Main criteria:
- Type of relay (electromechanical or electronic).
- Rated current (indicated on the case, for example, 5A or 10A).
- Compatibility with the compressor model (for example, Danfoss, Embraco).
Install the new relay in the reverse order, connecting the wires according to the photo.
Step 4. Checking operation
Turn on the refrigerator and listen:
- The compressor should start without long clicks.
- The relay should not get hot or make any extraneous sounds.
If the refrigerator started working, but after a few minutes it turned off again, check the voltage in the network or the condition of the compressor.
⚠️ Attention: Do not use relays from other models of refrigerators, even if they are similar in appearance. The operation parameters (current, delay time) may differ, which will lead to premature failure. compressor wear.
FAQ: Frequently asked questions about refrigerator starting relays
Can the relay be repaired or just replaced?
Mechanical relays with burnt contacts can sometimes be restored, by cleaning them with sandpaper (zero) or a file. However, this is a temporary solution - after 1-2 months the contacts will burn out again. Electronic relays are not repaired, only replaced.
How to determine that the relay is broken and not the compressor?
If the relay clicks, but the compressor does not start, disconnect it. relay and apply voltage directly to the compressor (to the working winding). If the motor hums, the relay is to blame. If not, the problem is in the compressor. Attention: this test must be performed by a specialist, as it requires working under voltage!
How much does a new relay cost and where is it? buy?
The cost of the relay depends on the type:
- Mechanical: 500–1500 rubles.
- Electronic: 1500–4000 rubles.
Can be purchased at repair service centers refrigerators, spare parts stores (for example 220-Volt, All-Zap) or on AliExpress (but be careful with compatibility).
What will happen if you do not replace the faulty relay?
If the relay does not start the compressor, the refrigerator simply will not freeze, and food It’s worse if the relay is “stuck” in the closed state - this will lead to overheating of the compressor and its failure (the cost of replacing a compressor is 5–10 times higher than the relay).
Is it possible to use a universal relay instead of the original one?
Theoretically, yes, but only if its parameters (operation current, time) delays, type of fastening) completely coincide with the original one. For example, a universal relay RBM-1 is suitable for many compressors Danfoss, but before purchasing you need to check the characteristics.