A sudden stop of the refrigerator compressor often causes panic, because this threatens food damage and expensive repairs. However, in many cases the problem lies not in the motor itself, but in a small and inexpensive element - the start relay. It is this unit that is responsible for starting the engine and its operation in normal mode, opening the starter winding circuit after gaining speed. If the relay fails, the compressor either hums but does not start, or clicks and is immediately turned off by the protection.
Checking this component is possible even for a home craftsman with a minimum set of tools, the main one of which is multimeter. Correct diagnosis allows you to avoid purchasing unnecessary spare parts and accurately determine whether the entire compressor needs to be replaced or whether it is enough to install a new relay. In this article, we will look in detail at how to remove the part, which contacts to pay attention to, and what resistance values are considered normal for a working device.
Before taking active steps, you need to make sure that the work is safe. Any manipulations with the electrical components of the refrigerator must be carried out only when the device is disconnected from the network. Ignoring this rule may result in electric shock or damage to the control electronics.
⚠️ Attention: Before starting any diagnostic work, be sure to disconnect the refrigerator from the power supply and wait for the capacitors to discharge (usually 2-3 minutes).
Design and principle of operation of the starting relay
The starting relay is an electromechanical device that controls the supply of voltage to the starter winding of the compressor electric motor. When the refrigerator is turned on, the motor rotor is stationary, and moving it from its place requires significantly more force than to maintain rotation. It is this task that is performed by starting windingwhich the relay connects for a split second and then turns off when the engine picks up the required speed.
There are two main types of relays found in household refrigerators: induction (with a coil) and posistor (thermal). Induction models operate using electromagnetic force: the current passing through the coil creates a magnetic field that draws in the core and closes the contacts. The posistor ones use the property of the ceramic element (posistor) to sharply increase the resistance when heated, actually opening the circuit of the starter winding. Understanding the type of relay you have is important to correctly interpret test results.
A malfunction most often manifests itself as an open circuit, when the contacts oxidize or burn, or as a short circuit, when the mechanism is stuck in the on position. In the first case, the engine hums but does not start; in the second, the compressor winding may burn out due to overheating. Therefore, timely diagnosis is critical to saving an expensive unit.
Structurally, the relay is usually enclosed in a plastic case, which is attached directly to the compressor terminals. The case is often marked with the model and connection diagram, which makes it easier to find analogues in case of replacement. Inside the case there are moving and fixed contacts, springs and, depending on the type, a coil or a posistor.
⚠️ Attention: If traces of plastic melting are visible on the relay body or a burning smell is felt, the part definitely requires replacement without additional checking.
Preparation for diagnostics: tools and safety
To carry out high-quality work on checking the start relay, you will need a minimum set of tools that most home craftsmen can find. The main device will be a multimeter capable of measuring resistance in the range from zero to several tens of kilo-ohms. You will also need screwdrivers to remove the compressor protective panel and, possibly, pliers to carefully remove the terminals.
It is important to select the correct position of the regulator on the multimeter. To check the integrity of the circuit and contacts, the dialing mode, indicated by the speaker symbol, is best suited. If your device does not have such a mode, you can use the resistance measurement mode Ohmby selecting the limit of 200 Ohm or 2 kOhm. In the dialing mode, the presence of a contact will be accompanied by a sound signal, which is much more convenient when working in limited light conditions.
Before starting the test, it is necessary to ensure good access to the compressor. It is usually located at the bottom rear of the refrigerator and is covered with a metal or plastic casing. After removing the casing, you will see a black barrel-shaped motor-compressor, to which a refrigerant tube and an electrical cable fit.
The next step is to carefully remove the relay itself. It fits onto three pins coming out of the compressor. Sometimes the relay is secured with a metal bracket or plastic latches. You must act carefully so as not to damage the wires or break the plastic case, which may be dry over time.
☑️ Preparing to check the relay
Visual inspection and removal of the relay
After the relay is removed from its seat, the first step is to carry out a thorough visual inspection. Often external signs can immediately indicate the nature of the malfunction, which will save time on instrumental diagnostics. Shake the relay next to your ear: if a clear knocking sound of a detached element is heard inside, this is a sure sign of destruction of the internal structure, and such a device cannot be repaired.
Inspect the contact groups and conclusions. Carbon deposits, black spots or oxidation on the contacts indicate a poor connection, which could lead to heating and failure of the unit. If the relay is a posistor, pay attention to the ceramic element: it must be intact, without cracks or chips. Cracks in the posistor often occur due to thermal shock during frequent switching on and off.
Check the condition of the wires going to the relay. The insulation should not be melted or cracked. If the wires turn black, this indicates that a current higher than the rated current passed through them, which could be caused by a malfunction of the compressor itself or an interturn short circuit.
Why can the relay burn out?
A frequent reason for the failure of the starting relay is poor-quality voltage in the network or turning on the refrigerator too often. If you turn off the appliance and immediately turn it on again, the compressor tries to start under pressure, which creates an overload. Always pause for at least 5-10 minutes before turning on the refrigerator again.
Special attention should be paid to the labeling. On many modern models, such as Indesit, Atlant or Beko, the connection diagram is printed directly on the relay cover. The arrow indicates the correct installation position: the inscription should be read horizontally and the arrow should point upward. Violation of this rule can lead to incorrect operation of the mechanism or its rapid failure.
Checking an induction relay with a multimeter
Induction relays, often used in older models of refrigerators and brand units Biryusa or Nord, have a control coil. Checking such a device begins with testing the coil. Switch the multimeter to resistance measurement mode and connect the probes to the coil terminals. The resistance of a working coil is usually several tens of Ohms (for example, from 30 to 60 Ohms), the exact value depends on the specific model.
If the multimeter shows one (infinity), then there is a break in the coil, and the relay will not be able to create a magnetic field for launch. If the resistance is close to zero, this indicates a short circuit of the turns, which is also a malfunction. In both cases, replacement of the component is required.
Next, the mechanical part is checked - the contacts. At rest (when the relay is lying on the table), the contacts of the starter winding should be open. When voltage is applied (under test conditions this is simulated manually or by applying current), they should close. Ring the contacts in different relay positions. If the contacts are “stuck” and show a short circuit constantly, the engine will not be able to switch to operating mode.
It is also important to check the thermal release if it is built into the relay housing. This is a bimetallic plate that opens the circuit when overheated. When cold, it should conduct current (resistance close to 0 ohms). When heated (which is difficult to check at home without special equipment), it should open the circuit.
Diagnostics of a posistor relay
Posistor relays, widely used in refrigerators LG, Samsung i Stinol, are structurally simpler, but their verification has its own characteristics. The main element here is a posistor - a ceramic resistor whose resistance depends on temperature. At room temperature, its resistance should be low (usually from 10 to 50 ohms), which allows current to flow freely through the starter winding when starting.
To check, connect the multimeter probes to the posistor terminals. If the device shows resistance within the specified limits, the element is most likely working. If the multimeter shows infinity or the resistance is significantly higher than normal (megaohms), the posistor is broken or dried out and requires replacement. It is noteworthy that visually a posistor may look intact, but not perform its function.
One of the features of posistors is their inertia. Once voltage is applied, they heat up and increase resistance, essentially turning off the starter winding. In order for the relay to work again, the posistor needs to cool down, which takes from 1 to 3 minutes. That is why you need to pause when trying to start the refrigerator again.
The table below shows approximate resistance values for various types of relays that will help you interpret the multimeter readings.
| Relay type | Element being tested | Normal resistance | Symptom of malfunction |
|---|---|---|---|
| Induction | Coil | 30 - 60 Ohm | ∞ (open) or 0 (short circuit) |
| POSISTOR | POSISTOR | 10 - 50 Ohm | > 100 Ohm or ∞ |
| Any | Contacts (rest) | 0 Ohm (closed) | ∞ (open circuit) |
| Any | Thermal protection | 0 Ohm | ∞ (in a cold state) |
Typical errors and possible malfunctions
When diagnosing the start relay, beginners often make mistakes that can lead to an incorrect diagnosis. One of the most common is trying to test the relay without completely disconnecting it from the compressor. In this case, the multimeter may ring the circuit through the motor windings, showing false results. Always check the relay as a separate, isolated element.
Another mistake is ignoring the state of the compressor contacts. Even if the relay is working properly, oxidized or burnt mating pins on the motor itself will not make contact. Clean them with fine sandpaper or a file before installing a new or tested relay. They also often forget to check the integrity of the wires coming from the thermostat or control board to the relay.
It is worth mentioning “symptomatic” treatment. If you change a relay because the previous one burned out, but the cause has not been eliminated (for example, power surges or rare defrosts leading to heavy duty operation), the new relay can also quickly fail. Compressor should operate normally, without overloads.
If after replacing the relay the refrigerator started working, but after a while it stopped turning on again or started humming, the problem may be deeper. This may indicate an interturn short in the motor windings or a loss of compressor performance (compression). In such cases, simply replacing the relay will only give a temporary effect.
⚠️ Attention: Never try to fix the relay contacts in a closed state ("block" it) to force it to start. This will lead to instant burning of the starting winding