A sudden stop of the refrigerator compressor is always an alarming signal that requires immediate intervention. Often the cause of a breakdown is not the motor itself, but a small but critical device - the starting relay. It is this component that provides the initial impulse to start the engine and protects it from overloads. If you notice that the refrigerator hums but does not start, or the compressor turns on for a couple of seconds and immediately clicks when it turns off, then diagnosing the relay becomes a priority.
To accurately determine the malfunction, you do not have to call a technician right away. Having a simple tool such as a multimeter allows you to carry out initial diagnostics at home with high accuracy. In this article we will look at how to correctly check the refrigerator relaywhat resistance values are considered normal and what to look for during a visual inspection. Video materials built into the training process will help you clearly see each stage of the procedure.
Modern refrigerators, be it Indesit, Atlant or Bosch, use similar operating principles of starting equipment. Understanding the physics of the process will help you avoid mistakes. The relay can be electromagnetic or posistor, and the methods for testing them have their own nuances. We will consider both options so that you can confidently handle the repair of equipment of any model.
The principle of operation and types of starting relays
Before you pick up a multimeter, you need to understand what exactly we are going to check. The start relay is an electrical switch that closes the compressor start winding circuit only at the moment of start. As soon as the engine reaches the required speed, the relay opens the circuit and the motor runs on the main winding. If this mechanism jams or burns out, starting becomes impossible.
There are two main types of devices that are found in household appliances. The first type is electromagnetic relayswhich can often be found in older models of refrigerators. They have a moving core and contacts that can burn over time. The second type is posistor (solid-state) relays installed in modern technology. They have no moving parts, and switching occurs due to changes in the resistance of a special ceramic element when heated.
⚠️ Attention: An attempt to replace a posistor relay with an electromagnetic one (or vice versa) without changing the connection diagram will lead to to compressor combustion. Always install a part with exactly the same marking code.
Visually, these devices are also different. Electromagnetic ones often have a more complex design with a coil and a lever mechanism, while posistor ones look like a compact plastic barrel with three contacts. Understanding the type of relay you have is critical to choosing a test method, although using a multimeter is universal for both cases.
Why do relays fail?
The main reason for a starting relay to burn out is frequent power outages or power surges in the network. Every time the light blinks, the compressor tries to start, putting a huge load on the relay contacts. Over time, the metal of the contacts burns out, or the posistor loses its properties, ceasing to conduct current of the required strength.
Preparation for diagnostics: tools and safety
Diagnostics of electrical devices requires strict adherence to safety rules. A refrigerator is a high-power device that operates on a 220-volt network. Any carelessness may result in electric shock or damage to electronics. Therefore, the first step is the complete preparation of the workplace and tools.
You will need the following set of tools for a quality check:
- 🔌 Multimeter (digital or analog) - the main device for measuring resistance and circuit integrity.
- 🪛 Set of screwdrivers - for removing the back cover of the refrigerator and dismantling the compressor casing.
- 🧤 Dielectric gloves - to protect hands when working with wiring.
- 🔦 Flashlight - to illuminate the compressor area, since it is often dark there.
Before starting any work, de-energize the refrigerator. Unplug the power cord from the outlet. Don’t just turn off the button if it is there, but disconnect it from the network. This will ensure that you won't get shocked if you touch the contacts. It is also recommended to move the unit away from the wall to provide convenient access to the rear panel.
☑️ Safety checklist before repair
After removing the rear protective panel, you will see the compressor - black “pan” at the bottom of the unit. A plastic box fits its terminals, in which our desired relay is located. Carefully remove this cover. It is often held in place by latches or screws. Be careful not to damage the wires going to the thermostat or other components.
Visual inspection and dismantling of the device
Removing the relay is a simple but important step. Usually it is simply put on the three pins of the compressor. However, before you pull, carefully inspect the mounting method. In some models, for example, in old ZIL or Biryusa, the relay can be fixed with a metal bracket or a plastic clamp.
After removing the device, carry out a thorough visual inspection. Often external signs speak of a problem louder than any measurements. Shake the relay near your ear: if something inside dangles and rattles like a dry knuckle, it means that the insides are destroyed and the part definitely requires replacement. The entire relay should not make sounds when shaking.
Pay attention to the condition of the plastic and contacts:
- 🔥 The presence of melts, soot or soot on the body indicates a short circuit or overheating.
- 💧 Traces of oxidation or rust on contact groups can interfere with normal current conduction.
- 💥 Cracks in the body of a posistor relay often indicate that the ceramic element has exploded due to a voltage surge.
⚠️ Attention: If you find traces of oil or a burning smell inside the relay casing, this may indicate not only a breakdown of the relay itself, but also problems with compressor sealing. In this case, simply replacing the relay may not solve the problem for a long time.
If visually the device seems intact, we move on to instrumental diagnostics. Clean the contacts from dust and dirt with a dry cloth. Make sure that the terminals that fit onto the compressor pins are not loose and are firmly in place. Weak contact is a common cause of sparking and subsequent failure.
Technology for checking with a multimeter (step by step)
Now comes the most important point - measuring the parameters. Switch the multimeter to resistance measurement mode (Ohms, denoted Ω). Typically this range is 200 ohms or 2 kohms. If you are using an analog dial gauge, first calibrate the zero by shorting the probes.
The testing process depends on the type of relay. For posistor relay (usually has 3 contacts) the algorithm is as follows:
- Find the contacts going to the starting winding. Usually these are two contacts located nearby.
- Touch these two contacts with the multimeter probes.
- The normal resistance of a working posistor at room temperature is from 10 to 60 Ohms.
- If the device shows infinity (number 1 on the left or OL) - the circuit is broken, the posistor is burned out.
- If the resistance is close to zero, a short circuit has occurred inside the element.
For electromagnetic relay the circuit is more complicated. Here you need to “ring” the coil and contacts. The coil resistance is usually 30-40 ohms. Connect the probes to the coil terminals. If the arrow does not move or the digital indicator shows a break, the coil has burned out. Next, we check the moving contact: in a vertical position it should close the circuit (resistance is close to 0), and when the relay is turned over, it should open.
Below is a table with approximate resistance values for various types of relays found in refrigerators of popular brands.
| Relay type | Normal resistance | Symptom of malfunction | Probable cause |
|---|---|---|---|
| Posistor (PTC) | 15 - 50 Ohm | Infinity or 0 Ohm | Destruction of the ceramic element |
| Electromagnetic (coil) | 30 - 45 Ohm | Infinity | Breakage of the coil winding |
| Electromagnetic (contacts) | < 1 Ohm (closed) | High resistance | Soot, oxidation, burning |
| Thermal protection relay | < 1 Ohm (cold) | Infinity | Bimetallic plate burnout |
Analysis of results and search for hidden defects
Having received the multimeter readings, you need to interpret them correctly. If you see values close to normal, this does not guarantee 100% serviceability. A posistor relay can show normal resistance when cold, but when voltage is applied, it instantly burns out or does not switch. This is called a “floating” fault.
Pay attention to the thermal protection relay, which is often built into the same housing as the starting one or located next to it. It is responsible for turning off the compressor when it overheats. Check its contacts: when cold they should be closed (ringing). If the multimeter shows a break, the thermal protection has tripped or burned out. This often happens after trying to start a stuck compressor.
A critical point that is often forgotten: checking the compressor windings themselves. If the relay burned out, it could have done so for a reason, but because of problems with the motor. Before installing a new relay, be sure to ring the three pins on the compressor. The resistance between them should be in the range of 10-40 Ohms. If you see a short circuit (0 Ohm) or an open circuit (infinity) between the motor terminals, replacing the relay will not help; repair or replacement of the compressor is required.
It is also worth checking the wires going from the relay to the connector. Sometimes the core inside the insulation breaks, especially at the very entrance to the relay housing. Move the wires when the multimeter's continuity mode is turned on - if the readings jump, it means that the contact inside the wire is broken.
Relay replacement and final assembly
If the diagnostics confirmed the relay is faulty, it must be replaced. It makes no sense to repair a burnt posistor or melt the contacts of an electromagnetic relay at home - the resource of such restoration will be minimal, and the risk of fire is high. Buy a new part strictly according to the article number or model of your refrigerator.
The installation process is simple: the new relay is put on the pins of the compressor. It is important to maintain orientation! The relay body usually has arrows UP or TOPthat should point up. Also ensure connection polarity if the connectors are not symmetrical. In some models LG or Samsung the connectors may differ in shape, which eliminates errors, but in older models you need to be careful.
⚠️ Attention: After installing the new relay, do not rush to close the back cover. Plug in the refrigerator and listen. The compressor should start with a characteristic hum, and after 10-20 seconds the relay click should turn off the starting winding (the hum may change slightly, becoming quieter). If there is no startup or the hum is intermittent, immediately turn off the power.
After making sure that operation is normal, assemble the casing and install the back panel in place. Do not leave the compressor unprotected, as this may lead to dust, moisture or accidental contact with working parts, which is dangerous.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay?
Theoretically, you can start the motor by applying voltage directly to the starting winding, but doing this is strictly prohibited in domestic conditions. This requires special skills, poses a risk of fire and will completely kill the compressor. A relay is a necessary element of protection and control.
Why does a new relay burn out after a short time?
If a new relay burns out quickly, then it is not the reason. Most likely, the compressor itself is faulty (interturn short circuit, wedge), there are problems with the wiring or unstable voltage in the network. Also, the cause may be incorrect installation (wrong side).
Where can I find the relay markings for purchase?
The markings are usually applied to the side or top edge of the plastic relay case. Look for a code of letters and numbers (for example, RT-12, 17.900.45.010). You can also search by refrigerator model in spare parts catalogs.
What is the difference between a relay for a single-compressor and a two-compressor refrigerator?
The operating principle is the same, but the physical dimensions and power may differ. Dual-compressor models often use less powerful compressors and, accordingly, more compact relays. The main thing is the coincidence of electrical characteristics and seats.