Sudden silence of the refrigerator or, conversely, its obsessive humming without cooling often indicates a breakdown in the compressor starting circuit. In most cases, the culprit is starting relay a small but critical component that supplies an impulse to the motor winding. If this element fails, the motor hums, clicks, but cannot start, which leads to heating of the housing and potential combustion of the windings.
Before calling a technician or buying a new compressor, it is worth conducting an initial diagnosis. Starting relay (or "relay" as it is called often called in everyday life) you can check it yourself using a minimal set of tools. This will save significant money, since the component itself is inexpensive, and the replacement procedure does not require complex equipment.
In this article we will analyze the design of various types of starting devices, methods for checking them with a multimeter and visual inspection. You will learn how to distinguish a burnt contact from a mechanical jam and when exactly a complete replacement of the unit is required.
Signs of a faulty starting device
The first step in diagnosis is to observe the behavior of the equipment. If compressor the refrigerator makes a loud click and immediately goes silent, or hums for a few seconds, and then there is a click again and there is silence - these are classic symptoms. The engine tries to start, receives a starting impulse, but the relay opens the circuit too early or does not close it at all.
Another alarming signal is heating of the compressor housing. If you put your hand to the back wall of the unit and feel that the motor is hot, although the refrigerator is not cooling, it means that current is flowing into the windings, but the rotor does not rotate. In such a situation the risk of burning out the motor windings reaches 90%if you do not disconnect the device from the network immediately.
It is also worth paying attention to the cyclical operation. A working refrigerator turns on and off as the temperature rises. If you hear constant attempts to start every 30-60 seconds, this indicates that thermal relay the protection is triggered due to an overcurrent caused by the inability to start.
⚠️ Attention: Long-term operation of a refrigerator with a faulty start relay can lead to an interturn short circuit in the compressor. In this case, repairs will become economically unfeasible.
Design and types of starting relays
To properly check the element, you need to understand the principle of its operation. There are two main types of devices that are used in modern and old models of refrigerators Indesit, Atlant, Beko and other brands. The first type is electromagnetic relays, which are more often found in old technology.
The second, more common type today is posistor (thermal) relays. Inside them there is a ceramic element (posistor), which, when voltage is applied, heats up and changes its resistance, opening the starting winding. The principle of operation is simple: in a cold state, the resistance is low, the current flows to the starting winding, the motor accelerates, the posistor heats up and turns off this winding.
Visually they may differ in the shape of the case and the number of contacts. Electromagnetic ones often have an elongated shape and a movable core, while posistor ones look like compact plastic boxes with three or four contacts. Understanding the type of your device will help you choose the right testing method.
How does a posistor differ from a regular resistor?
A posistor is a semiconductor element whose resistance increases sharply when heated. When cold, it passes current, starting the engine, and when heated from the passing current, it actually turns into a dielectric, breaking the starting winding circuit. A conventional resistor maintains a constant resistance.
Preparation for diagnostics and safety measures
Any work with electrical appliances requires compliance with strict safety rules. Before removing the relay, you must completely turn off the power to the refrigerator. It is not enough to simply turn it off with a button - you need to unplug the cord from the outlet. This will eliminate the risk of electric shock and short circuit.
To carry out diagnostics, you will need the following set of tools:
- 🔧 Screwdriver (Phillips or flat) for removing the casing.
- 🔌 Multimeter (tester) for continuity testing.
- 🧤 Dielectric gloves (recommended).
- 📸 Smartphone for photographing the connection diagram.
Remove the protective casing from the compressor. It is usually secured with latches or screws. Carefully remove the relay itself from the compressor contacts. It may hold tightly, so gently rock it from side to side. Before disconnecting the wires, be sure to take a photo of which wire is connected where, or draw a diagram so as not to mix up the terminals during assembly.
☑️ Checklist before starting the test
Visual inspection and check of the hammer relay
Start with an external inspection. If traces of burning, melted plastic or black spots are visible on the relay body, further inspection may not be required - the element is definitely faulty. Also pay attention to the condition of the contacts: oxidation or carbon deposits may prevent the flow of current.
Electromagnetic (hammer) relays are tested in an inverted state. In the operating position, the contacts are closed, but if you turn the relay over, under the influence of gravity the core should fall and break the circuit. If, when turning over, you do not hear a characteristic knock or the contacts remain closed (or open depending on the design), the mechanism is jammed.
Use the multimeter in continuity mode. Connect the probes to the contacts. In a normal position the chain should ring. When turned over, it breaks. If the multimeter shows resistance close to infinity in both positions, it means the coil is burnt out or the contacts are oxidized. If it shows zero in both cases, the contacts are “stuck.”
The table below will help you interpret the multimeter readings for various conditions:
| Relay state | Multimeter readings (Ohm) | Action |
|---|---|---|
| Good (normal position) | 0 - 5 Ohm (Closed) | Installation back |
| Good (inverted) | ∞ (Open) | Installation back |
| Burnt coil | ∞ in any position | Replacing the relay |
| Sticking contacts | 0 Ohm in any position | Cleaning or replacing |
Diagnostics of a posistor (thermal) relay
Checking a posistor relay has its own characteristics. Since its operation is based on changes in resistance when heated, a “cold” test with a multimeter will only show the integrity of the circuit, but does not guarantee correct operation under load. In a cold state, the resistance should be low (usually several tens of Ohms).
If the multimeter shows an open circuit (infinity) on a cold posistor, the element is definitely faulty. However, if there is resistance, this does not mean that the relay is working. There are cases when the posistor does not heat up to the required temperature or, on the contrary, heats up too quickly, preventing the compressor from accelerating.
To accurately check the posistor, experienced craftsmen sometimes use the method of briefly connecting to the network through a fuse, but this is dangerous for an untrained user. A safer method is to replace it with a known-good analogue. The cost of a posistor is low, so buying a new element for testing often saves time.
Relay replacement and test run
If the diagnostics show a malfunction, proceed with replacement. Install the new relay onto the compressor contacts, observing the orientation (usually the "UP" marking points toward the top). Place the wire terminals firmly onto the appropriate terminals. Make sure that the wires do not touch hot parts of the compressor or each other.
Attach the protective cover. Now you can turn on the refrigerator. In the first seconds, you will hear a characteristic click and rumble of the engine starting. If the compressor started working smoothly, without vibrations or repeated clicks, and after 10-15 minutes the chamber began to get colder, the repair was successful.
It is important to monitor the temperature of the new relay housing during the first hours of operation. It may become slightly warm, but should not be so hot that it is impossible to touch. If the heating is excessive, you may have selected a relay with unsuitable characteristics.
⚠️ Attention: Compressor specifications and starting equipment requirements may vary depending on the year and model. Always check the markings on the new relay with the data on the old one or in the manufacturer’s technical documentation.
Frequently asked questions (FAQ)
Is it possible to repair a burnt-out relay or just replace it?
In 95% of cases, the relay must only be replaced. Internal elements (posistor or coil) cannot be restored at home. Attempts to clean the contacts or glue the housing give a temporary effect and can lead to a fire.
Why does a new relay burn out after a week?
This may indicate a problem not in the relay, but in the compressor itself (turn-to-turn short circuit) or in the wiring of the refrigerator. Also, the cause may be unstable voltage in the network. In such cases, in-depth diagnostics of the motor is required.
Is a universal relay suitable for my refrigerator?
Universal relays exist, but they require precise tuning or current selection. It is best to look for an original analogue by the catalog number indicated on the body of the old device or compressor.
How to understand that the problem is in the relay, and not in the compressor?
If, when connecting a new working relay, the compressor starts and works, the problem was in the relay. If the symptoms repeat with the new relay (buzzing, clicking, does not start), there is a high probability of a malfunction of the motor itself or the starting winding.