The sudden stop of the refrigerator or its inability to maintain the set temperature often throws owners into a stupor. First of all, we check whether the light inside the camera is on, whether the power cord is intact and whether the plugs in the shield have been knocked out. However, the most common technical cause of compressor failure is the failure of the start relay. It is this small but critical element that is responsible for starting the engine and protecting it from overloads.
Understanding the operating principle of this unit allows you not only to diagnose a breakdown, but also save a significant amount on calling a technician. Start relay is an electromechanical switch that supplies current to the starting winding of the compressor only at the moment of start. As soon as the motor reaches the required speed, the device opens the circuit, leaving the motor running on the main winding. If this process is disrupted, the refrigerator either hums but does not start, or turns on and immediately turns off.
In this article we will look in detail at what this unit consists of, what types of devices are found in modern models and how to independently diagnose. It is important to understand that a complex physical process takes place inside a sealed circuit that requires precise synchronization. We will look at thermal and posistor mechanisms so that you could accurately determine the type of malfunction of your unit.
The main function of the starting relay in the cooling system
The main task of the device is to provide a short-term connection to the starting winding of the compressor motor. An asynchronous motor used in refrigerators cannot independently start rotating the rotor from a state of rest. It requires an additional impulse, which is created by a phase shift of the current in the starting winding. Time relay (starting) closes this circuit exactly for the period until the motor accelerates to 75% of the rated speed.
In parallel with the starting function, the device often acts as a protective mechanism. In most designs it is combined with a thermal relay or works in conjunction with it. If the current in the circuit exceeds permissible limits or the compressor overheats, the contacts open, preventing combustion of the motor windings. This is a critical aspect, since replacing the compressor is much more expensive than installing a new relay.
The startup process occurs automatically every time the thermostat or electronic module gives a command to cool. Operation cycle depends on the load of the chambers and the ambient temperature. The reliability of this unit directly affects the resource of the entire refrigeration unit. If the relay sticks or does not open the circuit in time, the starting winding can burn out in a matter of seconds.
Internal structure and types mechanisms
Structurally, devices are divided into two main types: induction (electromagnetic) and posistor (thermal). In older models of refrigerators, such as classic ZIL or Biryusaelectromagnetic relays were most often found. Their work is based on the physical movement of the core inside the coil under the influence of current. When the engine is stopped, the contacts are open. At the moment the voltage is applied, the current is high, the magnetic field draws in the core and closes the starting circuit.
Modern units, including models Indesit, LG i Samsung, are predominantly equipped with posistor relays. Inside them there is a ceramic element - a posistor, which at room temperature has low resistance and conducts current. When current passes, it heats up, its resistance increases sharply, and the starting winding circuit actually breaks. After cooling (the cycle takes several minutes), the resistance drops again and the device is ready for a new start.
Thermal protection is usually a bimetallic plate that bends when heated. It can be built into the relay housing or mounted directly on the compressor housing. Bimetallic element reacts to current and temperature, opening the general power circuit at critical values. This prevents fire hazards and failure of expensive equipment.
- 🔹 Electromagnetic relays operate due to the movement of the coil and core, characteristic of Soviet and early post-Soviet technology.
- 🔹 PTC devices use heating of a ceramic element to break circuits, are noiseless and compact.
- 🔹 Combined models combine both starting and thermal mechanisms in one housing, which simplifies replacement.
- 🔹 Solid-state relays (rarely) use electronic components without moving parts and are highly reliable.
Fault symptoms and primary diagnostics
It is possible to determine that the problem lies precisely in the trigger mechanism by characteristic signs. Most often, the owner hears the refrigerator trying to turn on, a clicking sound, a buzzing sound, followed by silence or a second click after a while. The compressor may be hot, but no cold is produced in the chambers. This is a classic symptom that starting winding does not receive a pulse or the protection instantly turns off the power.
Another alarm signal is frequent cyclic turning on and off of the motor with an interval of 10-20 seconds. This indicates that the thermal relay has tripped. If you hear a loud clicking and humming noise, but there is no startup, there is a 90% chance that the relay is faulty or the compressor is stuck. A visual inspection can also give results: a blackened case, a burning smell or melted plastic indicate overheating of the contacts.
Sometimes the refrigerator works, but does not turn off, working for wear. This may indicate that the relay contacts are “stuck” in the closed state, and the starting winding is constantly energized. This mode of operation is extremely dangerous and can lead to engine combustion in a short time. Diagnostics should be carried out immediatelyby disconnecting the device from the network.
⚠️ Attention: If after the relay clicks and the compressor hums, a shutdown occurs, do not try to immediately turn the refrigerator back on. Let the thermal relay cool down (10-15 minutes), otherwise you can completely burn the motor windings.
Step-by-step instructions for checking the relay
To carry out diagnostics, you will need to remove the device from the compressor. First, make sure the refrigerator is unplugged. Remove the rear cover at the bottom of the unit (crankcase) to gain access to the motor. The relay is usually mounted on the side or bottom of the compressor rod and secured with a bracket or plastic latches. Carefully disconnect the wires, having previously photographed their location.
The first stage of testing is visual and mechanical. Shake the relay near your ear. If a ringing or knocking sound is heard inside, it means the mechanism is damaged or the contacts are loose. Inspect the insides for burning, soot, or melting. If the housing is intact, you will need a multimeter to check the conductivity. Switch the device to continuity testing or resistance measurement mode.
Checking a posistor element requires care. Ring the contacts: when cold, the resistance should be low (tens of ohms). If the multimeter shows one (open) or zero (short circuit) in an unheated state, the element is faulty. For electromagnetic relays, the integrity of the coil and the mobility of the core are checked. It should move freely and return to its original position under the influence of gravity.
☑️ Algorithm for checking the relay
Table of main faults
Systematization of signs helps to quickly understand the essence of the problem. Below is a table linking symptoms to probable causes within the relay. Remember that an accurate diagnosis can only be made by a specialist with the appropriate equipment, but this data will help you navigate.
| Symptom | Probable cause in the relay | Action |
|---|---|---|
| Clicking, buzzing, shutdown | The contacts of the starting winding do not close | Replacing the starting element |
| The motor hums, but does not start | Sticking contacts or broken posistor | Diagnostics multimeter |
| Frequent on/off | Faulty thermal relay (bimetal) | Replacing the thermal relay |
| Burning smell, blackening | Short short circuit or overload | Urgent replacement of the unit |
| The refrigerator does not turn off | Contacts are stuck in the closed state | Replacement of the relay to avoid fire |
Replacing a faulty part usually does not require special skills other than caution. The main thing is to choose an analogue with identical current and voltage characteristics. Universal relays often require the selection of washers or adjustments, so it is better to look for the original part number. An incorrectly selected device may not start the compressor or, conversely, not protect it in the event of an accident.
Is it possible to temporarily start a refrigerator without relay?
Theoretically, you can apply voltage directly to the starting winding through a button, but doing this is strictly not recommended without skills. You risk burning out the compressor forever or causing a short circuit. This is an emergency measure only to check the motor itself.
Nuances of replacement and selection of analogues
When purchasing a new part, pay attention not only to the brand of the refrigerator, but also to the model of the compressor. Manufacturers of household appliances often use motors from different companies (for example, a refrigerator Beko may have a compressor Embraco or Secop). There is always a marking on the relay body. Look for codes like R600a (refrigerant type, indirectly indicates power) or specific series designations.
Pay special attention to the mounting method. Some relays simply snap onto the contacts, others have an additional frame or bracket. Orientation is also important: there are models for vertical and horizontal installation. If you place a relay designed for vertical installation horizontally, gravity will not be able to return the core or rod to its original position, and starting will not occur.
In some modern models with inverter compressors, there is no classic starting relay. There, starting and speed control are carried out by an electronic control module. Inverter systems do not have characteristic clicks during operation. If your refrigerator makes noise constantly and smoothly changes volume, and then stops without a click, the problem is most likely in the electronics or the motor itself, and not in the mechanical relay.
⚠️ Attention: Compressor specifications and starting hardware requirements may vary depending on the year of manufacture and specific series. Always check the markings on the body of the old relay with the new part before installation.
Frequently asked questions (FAQ)
Is it possible to repair an old relay if it is burnt out?
In most cases, repair is impractical. If the contacts are burnt, cleaning them will only give a temporary effect, since the geometry and properties of the metal are damaged. PTC resistors cannot be restored. It is easier and safer to buy a new device, which is inexpensive.
Why does the new relay click, but the refrigerator does not start?
This may indicate a malfunction of the compressor itself (an interturn short circuit, a wedge of the piston group) or a break in the motor windings. It is also possible that a relay with unsuitable current characteristics has been selected. Professional diagnostics of the motor is required.
How long does the thermal relay cool down after activation?
Usually the cooling process of the bimetallic plate takes from 2 to 15 minutes, depending on the degree of overheating and design. It is not recommended to forcibly cool it with water or a hairdryer, so as not to damage the internal contacts due to a sudden temperature change.
Is it dangerous to operate a refrigerator with a faulty relay?
Yes, it is dangerous. If the relay does not turn off the starting winding, it will burn out. If the protection does not work, the compressor may overheat and seize. In the worst case, the wiring may overheat and the plastic in the technical compartment may ignite.