Modern refrigerator is a complex electromechanical unit, where each element performs a strictly defined function, ensuring the safety of products. Many owners of household appliances are faced with a situation where the compressor hums, but no cold is produced, or the motor does not make any sounds at all. In such cases, most often the culprit is a small but critical component - relay. It is this unit that is responsible for starting and protecting the engine, without which normal operation of the cooling system is impossible.
Understanding that what does a relay do in a refrigeratorallows you not only to correctly diagnose a breakdown, but also to avoid expensive repairs in a service center. Replacing this part often takes only a few minutes and is inexpensive compared to replacing a compressor. In this article, we will analyze in detail the design of start-up protection mechanisms, their types, and also describe step-by-step the process of checking the serviceability of the element using simple tools.
The main function of the start-up protection mechanism
The main task of the relay is to ensure the correct start of the compressor motor. The refrigerator motor is an asynchronous type with a squirrel-cage rotor, which requires the creation of a rotating magnetic field to start. Starting winding turns on only for a short time to accelerate the shaft, after which it must be immediately turned off. If this does not happen, the winding will burn out and the compressor will fail. The relay automatically opens the starting winding circuit when the engine reaches the required speed.
The second, no less important function is thermal protection. During operation, the compressor heats up, and the current in the circuit may increase due to overloads or problems with voltage in the network. The thermal relay monitors the current and temperature of the motor housing. If the permissible values are exceeded, the bimetallic plate inside the relay bends and opens the contacts, completely de-energizing the unit. This prevents insulation melting and fire hazards.
⚠️ Attention: Operating a refrigerator with a faulty or missing start-up relay is strictly prohibited. An attempt to start the compressor directly or with a faulty protection will burn out the motor windings in a matter of seconds.
Thus, the relay acts as an intelligent switch and safety guard. It synchronizes the operation of the starting and working windings, ensuring a smooth start, and instantly responds to emergency situations. Without this component, the compressor resource would be exhausted after the first turn on.
Operating principle and internal structure
To understand why the relay fails, it is necessary to consider its internal design. Most classic refrigerators use electromagnetic start relays. Inside the housing there is a coil through which the current of the working winding of the motor passes. When voltage is applied, the current increases sharply, creating a magnetic field that draws in the core. This core mechanically closes the contacts, connecting the starting winding.
As soon as the compressor rotor begins to rotate, current consumption drops. The magnetic field weakens, and under the influence of gravity (or a spring), the core returns to its original position, opening the starting winding circuit. This cycle is repeated every time the refrigerator is started. The thermal relay uses bimetallic platewhich deforms when heated, breaking the electrical circuit.
- 🔌 Contact group -moving and fixed contacts responsible for switching the starting winding circuit.
- 🧲 Electromagnetic coil —creates a field for moving the core at the time of startup.
- 🌡️ Bimetallic element —a sensitive thermal protection component that responds to overheating.
There are also relays with a posistor (PTC), where the role of a switch is performed by a ceramic element that changes its resistance when heated. Such devices are considered more reliable, since they have no moving mechanical parts that could stick. However, classic electromagnetic models are still widespread in old and budget models of equipment.
Why does the relay click?
The characteristic click when the refrigerator is turned on is the sound of the start relay contacts opening. If the clicks are repeated frequently, but the cold does not come, it means that the relay cannot keep the contacts closed or the compressor is jammed.
Varieties of relays for different models of compressors
There are many modifications of relays on the household appliances market, and they are not always interchangeable. Choosing the right part depends on the type of compressor, its capacity and manufacturer. Incorrect installation of an unsuitable relay can lead to the fact that the engine either will not start or will work with overload.
The main division occurs according to the type of design: electromagnetic and posistor. Electromagnetic models are sensitive to spatial position - they can only be installed in a certain orientation (arrow up or down), otherwise the core will not be able to return to its original position under the influence of gravity. Posistor (PTC) are universal in orientation, but require time to cool down (about 1-2 minutes) before restarting.
Relays also differ in the number of contacts and the shape of the housing. Some models have one input and one output, while others have a more complex configuration with additional terminals for alarms or fan control. When selecting an analogue, it is important to take into account not only the appearance, but also the electrical parameters indicated on the marking.
| Relay type | Principle of operation | Sensitivity to position | Service life |
|---|---|---|---|
| Electromagnetic | Retraction of the core by current | High (orientation required) | Medium (mechanical wear) |
| Posistor (PTC) | Heating of the ceramic element | Low (universal) | High (no rubbing parts) |
| Thermal (protective) | Deformation of the plate from heating | Depends on the model | High |
Typical symptoms of a relay malfunction
Diagnostics begins with monitoring the behavior of the refrigerator. If you notice that compressor it hums for a few seconds, then there is a click and the motor stops, and after a while the cycle repeats - this is a classic sign of a faulty starter mechanism. The engine tries to start, the relay is triggered, but due to a breakdown it opens the circuit too early or cannot hold the contacts.
Another symptom is a complete lack of response to being plugged into the network. The light inside is on, the fan (if any) works, but the compressor is silent. In this case, the thermal fuse inside the relay could blow, breaking the power circuit completely. Also, a malfunction may be indicated by a burning smell or melted plastic in the area of the rear wall of the unit.
- 🔊 Frequent clicks —the motor hums for 3-5 seconds and turns off with a characteristic sound.
- 🔥 Overheating of the housing —the rear wall or the compressor itself becomes hot to the touch.
- 🚫 No startup —complete silence on the motor side when plugged in.
It is important to distinguish a relay failure from a malfunction of the compressor itself. If after replacing the relay the situation does not change, perhaps the problem lies in the interturn short circuit of the motor windings or mechanical jamming of the piston group.
Step-by-step instructions for checking a relay with a multimeter
For accurate diagnosis you will need multimeter (tester) and a minimum set of tools to remove the relay from the compressor. Before starting any work, be sure to disconnect the refrigerator from the power supply! This safety rule must not be violated.
Remove the protective cover from the back of the compressor and carefully disconnect the relay. It is usually simply slipped onto the motor contacts and secured with a bracket or latches. Visually inspect the body: the presence of soot, cracks or melted areas indicates that the part requires replacement without further inspection. If there are no external defects, we proceed to dialing.
☑️ Checking the relay with a multimeter
Switch the multimeter to resistance measurement mode (Ohm). First check the thermal protection: the probes are applied to the input and output contacts of the power circuit. The device should show zero or a value close to it. If the screen shows one or infinity, the circuit is broken, the relay is faulty. To check the trigger mechanism (in electromagnetic relays), you need to turn the part over. In a vertical position (as on a compressor), the contacts should be open (infinity), and in an inverted position, closed (zero).
Normal winding resistance:Working winding: 10-20 Ohm
Starting winding: 20-35 Ohm
Between the body and windings: Infinity
If you use a posistor relay, just ring its contacts. Resistance should be low (about 3-15 ohms) when cold. When heated with a hairdryer, the resistance should increase to infinity, but at home it is enough to check the integrity of the circuit in a cold state.
Replacing parts and precautions
The process of replacing a relay is technically simple, but requires care. After purchasing a new part, install it on the compressor contacts, observing the correct orientation. The relay housing and compressor cover often have arrows indicating the "UP" or "DOWN" direction. Incorrect installation of the electromagnetic relay will result in it not opening the starting circuit.
Attach the retaining bracket or latch. Make sure the wires are not pinched or touching the hot condenser tubes. Put on the protective plastic cover. Only after complete assembly can you plug in the refrigerator. The first start may take longer as the thermal relay needs time to stabilize.
⚠️ Attention: Never short-circuit the relay contacts to force the compressor to start! This can lead to instant wiring failure or fire if there is a short circuit in the system.
If after replacing the relay the refrigerator started working, but after a while it stopped freezing again, the reason may be a freon leak or a malfunction of the thermostat. In such cases, the relay may be operational, but it protects the compressor from running idle or in emergency mode.
Is it possible to repair an old relay if it is burned out?
Theoretically, the electromagnetic relay can be disassembled and the contacts can be cleaned of carbon deposits with fine sandpaper, and the plate can also be bent. However, this is a temporary measure. The reliability of such a repair is low, and the risk of the compressor breaking down again is high. The cost of a new relay is low, so it is more rational to replace it.
Why does the relay constantly click, even when the refrigerator is full?
Frequent clicks indicate that the compressor cannot gain speed. Reasons: low voltage in the network, jamming of the engine piston group or wear of the relay itself (weak spring or burnt contacts). This may also be a sign of a faulty starting winding.
What is the difference between relays for single-chamber and double-chamber refrigerators?
The main difference is the power and operating current. Compressors of two-chamber models are usually more powerful, so the relays for them are designed for higher currents. Installing a weak relay on a powerful motor will cause it to burn out quickly. Always focus on the power markings (for example, 1/4 HP, 1/3 HP).
How often do you need to change the relay in the refrigerator?
The relay does not have a scheduled replacement period and serves until a malfunction occurs. On average, the service life of a high-quality relay is 5-10 years, which often coincides with the life of the compressor. Frequent power surges can significantly reduce this period.