A sudden stop of the refrigerator often becomes an unpleasant surprise, especially when there are perishable foods in the chamber. One of the key elements that ensures the engine starts is the starting relay. It is this small block that supplies the initial impulse to the compressor winding, allowing it to start working.
If you notice that the refrigerator is humming but does not start, or the compressor clicks and immediately goes silent, the problem may lie in this unit. Diagnostics using a multimeter allows you to accurately determine whether a part is working properly or whether it requires replacement. This is a procedure that is accessible even to those who are not professional craftsmen, but have basic skills in working with electrical appliances.
In this article we will analyze in detail the algorithm of actions, the necessary precautions and technical nuances that will help you carry out your own diagnostics. Understanding the principle of operation starting mechanism will save you time and money on calling a specialist.
The principle of operation of the starting relay and its role in the system
The starting relay is an electromechanical device that automatically connects the starting winding of the engine to moment of launch. As soon as the compressor rotor reaches the required speed, the relay opens the circuit, leaving only the main winding to work. In modern models, most often there are posistor elements that change their resistance when heated, while in old refrigerators induction mechanisms with a coil were used.
The main task of the device is to provide a short-term jump in current necessary to overcome the inertia of a stationary piston. If this element fails, the compressor receives power only to the main winding, which is not enough to start. As a result, the engine only hums, trying to move, which can lead to its overheating and thermal protection.
Structurally, the relay consists of a housing, a contact group and an internal switching mechanism. Posistor, being the heart of the modern version, in a cold state it has low resistance, passing current. When current passes, it heats up, its resistance increases sharply, and the starting winding circuit actually opens. This physical process occurs in a fraction of a second and is repeated every time the refrigerator is turned on.
Necessary tools and safety measures
Before starting any work with electrical equipment, you must strictly follow the electrical safety rules. A refrigerator is a high-voltage device, and careless handling of wires can lead to serious consequences. The first and most important step is to completely disconnect the device from the power supply.
To carry out diagnostics, you will need a minimum set of tools. The main device will be a multimeter (tester), which will measure the resistance of the circuit and check for a short circuit. You may also need pliers, a screwdriver and possibly electrical tape to isolate the connections after checking.
- 🔌 Multimeter with resistance (Ohm) measurement function and continuity testing.
- 🪛 Set of screwdrivers for removing the compressor protective cover.
- 🧤 Dielectric gloves for additional hand protection.
- 🔦 Flashlight for illuminating the work area in the compressor niche.
Make sure the work area is well lit and the floor is dry. Do not perform diagnostics if there is water or high humidity nearby. After turning off the refrigerator, wait 10-15 minutes so that the residual charge in the capacitors has time to dissipate, although in household models this is rarely dangerous, but it doesn’t hurt to be on the safe side.
⚠️ Attention: Never touch the metal parts of the compressor or wiring with wet hands. Even when the device is unplugged, the capacitors can retain a charge that can cause an unpleasant electric shock.
Check the integrity of the multimeter probes before starting work. The insulation must not be cracked or damaged, otherwise the meter readings may be incorrect and the risk of electric shock will increase. If you are using a pointer analog tester, make sure that it is calibrated.
Relay dismantling and visual inspection
After all precautions have been observed, you can begin to remove the part. The relay is usually located at the bottom of the refrigerator, at the back, directly on the compressor housing. It is covered with a plastic or metal casing, which is secured with latches or screws.
Carefully remove the protective cover. In most modern models, the relay is simply snapped onto three contacts of the compressor. However, before tightening it, you need to photograph or sketch the connection diagram. This will help avoid mistakes during reassembly, since the location of the contacts may differ from one manufacturer to another.
☑️ Preparation for dismantling
After removing the part, carefully inspect its body. There should be no traces of burning, melted plastic or cracks. If you see black spots or smell burnt insulation, this is a sure sign that it contact group has overheated. In this case, further testing may be a formality, since the part clearly requires replacement.
Shake the relay near your ear. If a ringing or knocking sound is heard inside of a detached element, this also indicates mechanical destruction of the internal components. PTC models often fail due to thermal expansion of materials, which leads to loss of contact inside the housing.
Is it possible to restore a burnt-out relay?
Restoring a starting relay, especially the posistor type, is not economically feasible. The cost of a new original or compatible part is low, and the reliability of the refurbished unit will be questionable. Attempts to clean the contacts or replace the posistor manually often lead to repeated failure after a short time.
Multimeter testing technology: step-by-step instructions
The most reliable diagnostic method is to measure resistance. To do this, switch the multimeter to resistance measurement mode (denoted as Ω or Ohm). If your device has a dialing mode with an audible signal, you can use that, but digital resistance values will give a more accurate picture of the condition of the part.
Identify the contacts on the relay. There are usually three or four, depending on the model. Two contacts are responsible for the main winding, one or two for the starting winding. There are often markings on the case: R (Run - working), S (Start - starting) and C (Common - general). If there are no markings, you will have to navigate by the location of the pins relative to the compressor.
The measurement process is as follows:
- Attach the multimeter probes to the contacts corresponding to the main winding. The device should show a resistance in the range from 10 to 30 ohms. This is a normal indicator for a working engine.
- Switch the probes to the contacts of the starting winding. Here the resistance should be higher, usually from 30 to 60 ohms, since the starting winding wire is thinner.
- Check the resistance between the relay body and any of the contacts. In good condition, the device should show infinity (one on the left side of the digital multimeter screen).
If the multimeter shows zero or a value close to zero, this indicates a short circuit in the windings or inside the relay itself. If the device shows infinity where there should be resistance, it means in the circuit break. In both cases, the relay is considered faulty.
Pay special attention to checking the posistor. When cold it should have low resistance. If immediately after connecting to the network (which is not recommended to do without a load) or when making a call it behaves like a diode or has an unstable resistance, its functionality is impaired.
Analysis of results and fault table
Interpreting multimeter readings requires understanding what exactly we are measuring. The resistance of the compressor windings is an indirect test of both the relay and the engine itself. If the relay is working properly, but the engine does not start, the problem may be deeper.
| Multimeter readings | Between which contacts | Probable cause | Actions |
|---|---|---|---|
| 0 Ohm (Short circuit) | Any pair of contacts | Short circuit inside the relay or windings | Replacing the relay, checking the compressor |
| ∞ (Infinity) | Working or starting winding | Circuit break, winding burnt out | Relay replacement or compressor repair |
| Normal (10-60 Ohm) | Between windings | The electrical part is OK | Checking the mechanical part, thermal relay |
| Any value | Contact and housing | Insulation breakdown on the housing | Urgent replacement of a part, life-threatening |
It is important to understand that normal values resistances may vary slightly depending on the engine temperature and the specific refrigerator model Indesit, Atlant or Beko. However, the order of the numbers must be preserved: the starting winding always has greater resistance than the working winding.
If the readings correspond to the norm, but the refrigerator still does not work, the problem may be that the compressor piston group is jammed. In this case, the relay clicks, trying to start the engine, but a mechanical obstacle prevents the rotor from turning. For accurate diagnostics in this case, you need to measure the starting current with special clamps.
Replacement of the faulty element and first start
If the diagnostics confirmed the malfunction, you need to purchase an analogue. When choosing, pay attention not only to the refrigerator model, but also to the markings of the relay itself. There are universal models, but it is better to look for the original spare part number or a complete analogue in the catalog.
Installation of a new relay is carried out in the reverse order of removal. Make sure the pins fit tightly into the sockets and the latches click into place. Do not use excessive force to avoid breaking the plastic housing or bending the compressor contacts.
⚠️ Attention: Before final assembly of the casing, it is recommended to conduct a test run. Plug in the refrigerator and listen. The compressor should start with a characteristic hum, after a few seconds the click of the relay should turn off the starting winding, and the engine will continue to operate smoothly.
If after replacing the relay the situation repeats (clicking and stopping), immediately turn off the device. This may mean that the problem is not in the relay, but in the compressor itself or in the heat removal system. Long-term work with a faulty starting mechanism can completely destroy an expensive unit.
Make sure that the capacitor (if your model has one separately from the relay) is also in good condition. In some circuits, it is paired with a starter and helps create a phase shift to start the engine. Its swelling or loss of capacity also interferes with normal operation.
Frequently asked questions about diagnostics and repair
Is it possible to check relay without a multimeter?
It is impossible to accurately check the resistance without instruments. However, you can use the elimination method: if you are sure that the socket and cord are working properly, but the compressor does not start, and the relay makes clicking noises, the probability of its malfunction is high. You can also gently shake the relay: if something dangles inside, it is definitely faulty. But for a 100% guarantee, you need a tester.
Why does a new relay burn out after a short time?
A common cause of repeated combustion is a malfunction of the compressor itself. If the piston group is jammed or the motor windings are defective, the starting currents become abnormally high. The relay, trying to start the engine, overheats and fails. In such cases, professional motor diagnostics are required.
What is the difference between a posistor relay and an induction relay?
A posistor relay works on the principle of changing the resistance of a solid-state element when heated. It is more compact and cheaper. Induction (electromagnetic) uses a coil and a movable core to open contacts. They are not always interchangeable, as they have different response characteristics and dimensions.
Is it dangerous to operate a refrigerator with a faulty relay?
Operation is impossible, since the refrigerator will not freeze. However, leaving the device plugged in when the relay is faulty is dangerous. The compressor will continually try to start, drawing high current, causing the wiring to overheat, melt the insulation, and potentially cause a fire. At the first sign of a malfunction, the device must be de-energized.