A sudden stop of the refrigerator compressor or its inability to start often indicates a faulty start relay. This small but critical element is responsible for supplying voltage to the motor windings at the moment of start. If you are faced with the fact that the refrigerator hums, but does not start, or, conversely, the motor is silent, but the light inside is on, the first thing that comes to the mind of an experienced technician is to check this particular unit.
Self-diagnosis allows you to save time and money, since replacing the relay is one of the simplest procedures for repairing household appliances. However, it is important to understand that starting relay is not just a switch, but a device with complex internal logic that depends on physical processes. Incorrect diagnosis can lead to the purchase of unnecessary spare parts or, worse, to failure of the compressor itself.
In this article we will take a detailed look at what the device looks like, what types of relays exist and how to use a multimeter to determine whether it is time for a replacement. You will learn to distinguish a burnt part from problems with the wiring or the engine itself.
The design and principle of operation of the starting relay
To understand the testing process, you need to understand what exactly we are diagnosing. The start relay (often called a start relay) is attached directly to the compressor housing. Its main task is to briefly apply voltage to the starting winding of the electric motor to create torque. As soon as the rotor picks up speed, the relay must turn off the starting winding.
There are two main types of devices that are found in modern and old models of refrigerators. Electromagnetic relays (often labeled as PZR, RTK) work based on current: when starting, the current is high, the magnetic field draws in the core and closes the contacts, when accelerating, the current falls, and the spring opens the circuit. Posistor relays (marking P-1, RT) they use a thermistor, which is heated by the passing current and loses conductivity, breaking the starting winding circuit.
⚠️ Attention: In older models there may be a mercury switch inside the relay. Be extremely careful when disassembling such devices to avoid breaking the glass capsule. Modern analogues usually do not contain mercury.
A bimetallic plate is also often mounted inside the housing thermal protection , which opens the contacts when the compressor overheats. This prevents the motor windings from burning out. When diagnosing, it is important to check not only the starting function, but also the integrity of the protection circuit.
What is the difference between a posistor and an electromagnetic relay?
Electromagnetic relays make a click during operation, while posistor relays are almost silent (except for the click of thermal protection). PTC resistors are more reliable, but are sensitive to power surges in the network.
External signs of malfunction and primary diagnostics
Before taking up the tools, it is worth analyzing the behavior of the refrigeration unit. Characteristic symptoms suggest with a high degree of probability that the relay is broken even before opening the back panel. If you hear a characteristic click, followed by the hum of the motor, and then another click and silence - this is a classic picture of a faulty starter. The compressor tries to start, the relay gives a pulse, but if the engine does not start, the current does not drop (in electromagnetic models) or the posistor does not turn off the winding in time, which leads to thermal protection tripping or contact burnout. A visual inspection of the part itself can also provide a lot of information. faulty starter.
The compressor tries to start, the relay gives a pulse, but if the engine does not start, the current does not drop (in electromagnetic models) or the posistor does not turn off the winding in time, which leads to thermal protection tripping or contact burnout. A visual inspection of the part itself can also provide a lot of information.
- 🔥 Burning smell: If, when removing the relay, you feel a sharp smell of burnt plastic, the part definitely requires replacement.
- 🔊 Extraneous sounds: Rumbling or rattling inside the relay case when shaken (if there are broken contacts or core).
- 🌡️ Overheating: Excessive heating of the relay body during operation, which can be noticed even without instruments.
Sometimes the problem lies not in the relay itself, but in oxidized contacts on the connector or burnt ones wires Therefore, the initial inspection should include checking the condition of the terminals. If the contacts are blackened, cleaning them can temporarily solve the problem, but it is better to replace the entire assembly.
Necessary tools and safety measures
Checking the relay on the refrigerator with your own hands is a simple procedure, but requires compliance with strict electrical safety rules. The most important rule: all manipulations are carried out only with completely disconnected from the network an electrical appliance. The plug must be removed from the socket, and not simply turned off with the toggle switch.
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be a multimeter (tester) configured to measure resistance (Ohm) or continuity. You may also need pliers, a screwdriver and possibly fine sandpaper to clean the contacts.
☑️ Safety check before repair
Do not forget that the compressor may be hot if it has just been running. Let it cool for 15-20 minutes before starting work. This will protect you from burns and allow you to more accurately check the thermal protection, which can be opened when hot.
How to remove the relay from the compressor
Access to the start relay is usually located at the bottom of the refrigerator, at the back. You will need to remove the protective cardboard or metal cover covering the engine compartment. Fastening can be carried out using latches or screws.
The relay itself is mounted on three pins coming out of the compressor housing. It is fixed either due to a tight fit or an additional bracket. Carefully remove the retaining bracket (if equipped) and pull the relay down. Do not use excessive force to avoid damaging the compressor leads.
At this stage, it is important to remember or photograph the position of the wires. Although it is difficult to confuse them due to different pin lengths and markings, visual fixation will help to avoid errors during assembly. Pay attention to the markings Start (start) and Run (operation) on the body of the part.
⚠️ Attention: When removing the relay, act carefully. If a part is stuck or strongly oxidized, do not jerk it sharply. Light rocking from side to side will help loosen the fit without damaging the ceramic insulators.
Visual inspection and checking with a multimeter
After removing the device, you can begin detailed diagnostics. A visual inspection often reveals obvious defects: melted plastic, blackened contacts, cracks in the case. If the relay is a posistor, you can carefully open it (if the design allows) and inspect the ceramic element for chips.
The main method of checking is testing with a multimeter. Switch the device to resistance measurement mode. For electromagnetic relays, the circuit is checked between contacts that must be closed at rest (normally closed thermal protection contacts). The resistance should be close to zero.
For posistor relays, the test is a little more complicated. In a cold state, the resistance between the contacts of the starting winding should be low (tens of ohms). If the multimeter shows infinity or, conversely, zero, the part is faulty. Thermal protection is also checked: it should “ring” (show zero) in a cold state.
| Relay type | What we check | Normal reading | Symptom of failure |
|---|---|---|---|
| Electromagnetic | Protection contacts | 0 Ohm (closed) | Infinity (open) |
| Electromagnetic | Start contacts | Open | Short-circuited |
| Posistor | Posistor resistance | 10-50 Ohm (cold) | ∞ or 0 Ohm |
| Any | Appearance | The whole body | Cracks, burning, soot |
Replacing the relay and starting the system
If the diagnostics showed a malfunction, the only correct solution is to replace the part with a similar one. It is important to choose a relay with exactly the same markings or a complete technical analogue. Installing a relay that is not suitable for the current or type can lead to the compressor burning out.
The installation process is the reverse of removal. Push the new relay onto the compressor pins as far as it will go. Make sure that the marking Top or arrow ↑ on the relay body is facing up, as required by the instructions. This is critical for the correct operation of the mechanism.
After connecting the wires and fixing the bracket, reassemble everything in the reverse order. Plug in the refrigerator. Normal starting should occur with a characteristic click, followed by a smooth hum of the running motor. If the clicking sounds are repeated and the motor does not start, immediately turn off the power.
⚠️ Attention: Compressor specifications and starting relay requirements may vary depending on the manufacturer and year of manufacture. Always check the markings of a new part with the original or technical documentation of your refrigerator model.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay?
Theoretically, you can start the engine by applying voltage directly to the starting winding, but this is strictly not recommended without special knowledge. This can lead to instantaneous burnout of the windings or a fire. A relay is an essential safety element.
Why does a new relay burn out immediately after installation?
Most often, the reason lies in a malfunction of the compressor itself (interturn short circuit, jamming of the piston group) or problems with the voltage in the network. If the compressor “pulls” too much current, it will quickly damage even a working relay.
How to distinguish a bad relay from a bad capacitor?
Some circuits (especially old ones) use a starting capacitor. If it swells or leaks, it is faulty. The relay is checked by checking the contacts. Often these elements are changed in pairs, since the failure of one could damage the other.
How much does it cost to replace a relay?
The cost of the part itself varies from 300 to 1500 rubles, depending on the model of the refrigerator and the type of relay. The work of a replacement technician usually costs more than the spare part itself, so self-repair is economically feasible.