The sudden stop of operation of a refrigeration unit often takes you by surprise, especially when there are perishable products inside. If you notice that the compressor is trying to start, making a clicking or humming noise, but then goes silent after a few seconds, the problem most likely lies in the starting device. It is this small unit that is responsible for supplying voltage to the motor windings, allowing it to gain the necessary speed.
Before calling a technician or buying expensive spare parts, it makes sense to carry out initial diagnostics yourself. To do this, you will need a minimum set of tools, the main one of which is a multimeter. Checking the relay - the procedure is not the most complicated, but it requires care, compliance with safety precautions and an understanding of the basic principles of the operation of electrical circuits.
In this article we will look in detail at how to determine the type of faulty unit, how to properly prepare the device for measurements and what indications are on the screen multimeter indicates a breakdown. Competent diagnostics will help you save time and money, and also understand whether it is worth changing the part or whether the problem lies deeper, for example, in the compressor itself.
Types of starting relays and the principle of their operation
To successfully carry out diagnostics, you need to understand what kind of device you are dealing with. In household refrigerators, there are most often two main types of starting devices: posistor (thermal) and induction (electromagnetic). The principle of their operation is radically different, which affects the testing methodology.
Posistor relay works based on the properties of a ceramic element (posistor) to change its resistance when heated. When cold, it passes current, allowing the engine to start. When current passes, the posistor heats up, its resistance increases sharply, and the starting winding circuit opens. This process only takes a few seconds. If the posistor is “broken,” the circuit does not open, and the engine burns out, and if it is broken, the motor will not start.
Induction devices, often called “tablets” or “barrels” because of the shape of the housing, use an electromagnetic coil. When voltage is applied, current passes through the starting winding, the magnetic field draws in the core, which closes the contacts. After starting the engine, the current drops, the core, under the influence of gravity or a spring, returns to its original position, opening the circuit. Mechanical contacts the inside of such relays often burns or sticks, which is the main reason for their failure.
Preparation for diagnostics and technology safety
Any work related to the electrical components of the refrigerator requires strict adherence to extreme caution. The compressor operates on 220 volts, which poses a real threat to life. The first and most important step is to completely disconnect the refrigerator from the power supply. Don’t just turn off the button, but unplug the cord from the socket.
To carry out the work you will need:
- 🔧 Phillips and flat-head screwdrivers for removing the casing.
- 🔌 Multimeter (tester) with the function of continuity and resistance measurement.
- 🧤 Dielectric gloves (recommended).
- 📸 Smartphone for photographing the connection diagram before disassembling.
After turning off the refrigerator, you need to gain access to the compressor. It is usually located at the lower rear of the unit. Remove the protective cardboard or metal panel covering the engine compartment. You will see a black “pot” of the compressor, to which a small plastic or metal box is attached - this is the device we are interested in. Carefully remove it, having first photographed the position of the wires.
⚠️ Attention: Even after disconnecting from the network, a residual charge may remain in the capacitors. Before touching the metal contacts of the relay, wait 5-10 minutes or carefully short the contacts of the power plug (if it is connected to a long wire) through the dielectric to eliminate the risk of electric shock.
Visual inspection and initial condition assessment
Before handling multimeter, conduct a thorough visual inspection of the removed assembly. External signs often allow you to immediately determine the nature of the breakdown without complex measurements. Shake the relay next to your ear: if you hear a clear ringing or knocking sound inside, this means that the internal contacts or mechanical elements have become detached or destroyed.
Inspect the housing for melting, blackening or cracks. The presence of burning or the characteristic smell of burnt plastic is a sure sign that a short circuit or overheating has occurred inside. If you see traces of oxidation on contact groups or terminals, this may also be the cause of poor contact, although often oxidation is a consequence, not a cause.
For posistor relays, the condition of the ceramic element itself is critical. If it is crumbled, blackened or has visible chips, its functionality is impaired. In induction relays, pay attention to the movable core: it should move freely inside the coil and should not be rusted or jammed.
Instructions: how to test a relay with a multimeter
Diagnostics with a multimeter is the most reliable way to determine the performance of a component. Switch the device to resistance measurement mode (Ohms) or dial-in mode (usually indicated by a speaker icon). If you use the dialing mode, the device will emit a sound signal when the circuit is closed.
Let's consider the testing algorithm for different types of devices. To induction relay it is necessary to check the integrity of the coil and the condition of the contacts. Apply the probes to the input and output contacts of the coil: the device should show a slight resistance (from 30 to 200 Ohms, depending on the model). If the screen shows one or infinity, the coil is broken, the relay is faulty.
Next, check the contacts. In a normal (open) state, the resistance between them should be infinite. If you turn the relay over (simulating a start), the contacts should close and the device will show zero or a value close to it. Lack of reaction indicates a mechanical breakdown or severe burning of the contacts.
For positor relay checking is even simpler. Measure the resistance between the contacts to which the posistor is connected. When cold it should be low (3 to 50 ohms). If the device shows infinity, the element is broken. If zero, a short circuit is possible, although for posistors this is less typical than destruction of the structure.
☑️ Relay diagnostic checklist
Table of typical resistance values and faults
For ease of interpretation of measurement results, use the table below. It will help you quickly navigate the instrument readings and draw the correct conclusion about the condition of the part.
| Relay type | What we check | Normal reading | Failure sign |
|---|---|---|---|
| Induction | Coil resistance | 30 - 200 Ohm | Infinity (break) or 0 Ohm (short circuit) |
| Induction | Contacts (at rest) | Infinity | Resistance less than 10 Ohms (sticking) |
| Posistor | Posistor resistance | 3 - 50 Ohm | Infinity or a sharp jump when heating |
| General | Case insulation | Infinity | Any resistance value (breakdown to the body) |
It is important to understand that resistance values may vary slightly depending on the manufacturer and model of the refrigerator, be it Indesit, Bosch or Atlant. However, the order of magnitude always remains similar. If you see values that differ radically from the table ones, the part requires replacement.
Why can a relay burn out immediately after replacement?
A common reason for a new relay to burn out again is a malfunction of the compressor itself. If the motor is “jammed” or there is a short circuit in its windings, the starting device takes on a huge current and burns out in seconds. Always check the resistance of the compressor windings before installing a new relay.
Replacement of a faulty relay and first start-up
If diagnostics showed a malfunction, you must purchase a similar part. You need to search by the markings indicated on the body of the old relay, or by the model of your refrigerator. There are no universal solutions here: a relay from one brand may not fit another due to differences in contact geometry and current characteristics.
Installation of a new part is carried out in the reverse order. Make sure the relay is seated tightly and the wires are connected according to your photo. Avoid kinking the wires and preventing moisture from entering the casing. After assembly, do not rush to load the products.
Plug in the refrigerator and listen. The compressor should start with a characteristic hum, the relay may click once at start, but then smooth operation should occur. If after 10-15 seconds the click is heard again and the engine stalls, the problem is not solved. The compressor itself or the thermostat may be faulty.
⚠️ Attention: Do not leave the refrigerator running unattended in the first 30-40 minutes after repair. This will allow you to notice sparking, smoke or repeated failure in time and prevent fire.
Frequently asked questions (FAQ)
Is it possible to repair a relay if the contacts are simply burnt?
Theoretically, the induction relay can be disassembled (if it is not sealed in plastic) and the contacts can be cleaned with fine sandpaper. However, practice shows that such a measure gives only a temporary effect. The metal of the contacts has already been altered by the arc, and soon they will stick again. It is safer and safer to buy a new part, the cost of which is usually low.
Why does a new relay burn out immediately after installation?
This is an alarming signal. Most likely the problem is not in the relay, but in the compressor. If the refrigerator engine is “heavy” (stiff piston movement) or has a breakdown of the windings, the starting current exceeds the norm by several times. The relay acts as a fuse and burns out to protect the wiring. In this case, motor diagnostics are required.
How to distinguish a relay from a thermal relay?
The starting relay is attached directly to the compressor terminals (often together with a thermal protector). The thermostat (thermostat) is usually located inside the refrigerator compartment or in the control unit and has a long capillary tube with a sensitive element at the end, which measures the air temperature.
Can a refrigerator operate without a start relay?
No, it cannot. Without a starting device, a single-phase asynchronous compressor motor will not be able to produce starting torque. It will only hum and heat up until the thermal protection works or the winding burns out.