The operation of a household refrigerator is based on the cyclic process of compression and expansion of the refrigerant, and the heart of this system is the motor-compressor. Many owners of household appliances are wondering how exactly the engine happens after inactivity and what makes it turn on again and again to maintain the cold. Understanding this mechanism is necessary not only for general development, but also for the initial diagnosis of malfunctions when the refrigerator stops freezing or starts working without stopping. initial start engine after being idle and what causes it to turn on again and again to maintain the cold. Understanding this mechanism is necessary not only for general development, but also for the initial diagnosis of faults when the refrigerator stops freezing or starts working without stopping.
The process of activating the electric motor is not instantaneous and direct, like turning on a light bulb. This is where a complex chain of interactions between temperature sensors, electrical relays and the windings of the motor itself comes into play. If you hear a characteristic hum, clicks, or, conversely, silence instead of the expected noise of a running unit, these are direct signals about the state of the starting system. In this article, we will analyze in detail the physics of the process so that you can distinguish normal operation from a critical breakdown.
It is important to understand that modern models, such as Liebherr or Electrolux, can use inverter technologies, where the starting principle is radically different from classic linear compressors. However, the classic start relay circuit remains the standard for millions of devices produced over the past decades. It is on this that we will focus our attention, since it is the most transparent for understanding and diagnostics at home.
The role of the thermostat in starting the system
The entire chain of actions begins not with the motor, but with the sensor that controls the temperature inside the chambers. Thermoregulator (or thermostat) is a mechanical or electronic device that opens and closes the electrical circuit depending on the heating of the evaporator. When you set the adjustment knob to a certain value, you set the threshold at which the contacts inside the thermostat will close, applying voltage to the compressor starting circuit.
When the temperature in the refrigerator rises above a set level (for example, after opening the door or loading warm food), a bimetallic strip inside the thermostat straightens up. This physical movement closes the contacts and electrical current flows to the motor windings. If at this moment you do not hear any sounds, the problem may not be in the motor, but in the sensor itself, which simply does not “see” the need for cooling.
⚠️ Attention: If you forcibly close the thermostat contacts to check, make sure that the compressor is working. Prolonged operation without temperature control can lead to freezing of the evaporator or spoilage of food.
Electronic control systems, often found in brands like Samsung or LG, use thermistors instead of mechanical plates. In this case, the signal about the temperature increase is processed control module, which programmatically makes a decision to start. This allows you to implement complex algorithms, for example, a turn-on delay to protect the network or synchronization of the operation of several compressors in dual-circuit systems.
Design and operation of the starting relay
The key element that ensures the start of an asynchronous motor is the starting relay. Asynchronous motors used in refrigerators cannot independently start rotating the rotor; they require an external push and the creation of a rotating magnetic field. Starting relay is responsible for the short-term connection of the starting winding, which creates the necessary phase shift.
Classical induction-type relays use a coil connected in series with the working winding of the motor. At the moment of switching on, the current is high, the magnetic field of the coil draws in the core, which mechanically closes the contacts of the starting winding. As soon as the rotor picks up speed, the current drops, the core, under the influence of gravity or a spring, returns back, opening the starting winding circuit. This cycle lasts a fraction of a second, but it is critical for starting.
More modern solutions use posistors (PTC relays). These are ceramic elements whose resistance increases sharply when heated. When voltage is applied, the posistor is cold and passes current to the starting winding. The current heats the crystal, its resistance increases, and the current almost completely stops. This approach is more reliable, since the device has no moving mechanical parts that are subject to wear.
Why does the relay sometimes click repeatedly?
If the relay clicks every few seconds, this means that the motor is trying to start, but cannot turn the shaft. The thermal protection relay opens the circuit, the motor cools down, and the cycle repeats. This is a common sign of a jammed compressor or a malfunction of the starting device itself.
Failure of this unit is one of the most common reasons why the compressor hums but does not start. If the relay contacts are burnt or the posistor is broken, the starting winding will not receive a pulse, and the engine will remain standing, consuming current only through the working winding, which will quickly lead to its overheating and tripping of the protection.
Electrical circuit: working and starting windings
To understand how the compressor turns on, it is necessary to consider its internal structure electric motor. The motor stator has two main windings: working (main) and starting. The working winding occupies two-thirds of the stator slots and has a larger wire cross-section, which allows it to operate continuously. The starting winding is made of a thinner wire and is turned on only at the moment of start.
The connection diagram is organized in such a way that the current first passes through the working winding and the relay coil (or posistor). This creates a magnetic field, but it is not enough to cause rotation. At the same time, current is supplied to the starting winding through the closed relay contacts. The interaction of the fields of two windings, shifted in space and in phase, creates a torque that tears the rotor from its place.
An important element of the circuit is capacitor, which is often connected in series with the starting winding. Its task is to increase the starting torque and shift the phase of the current, making the start softer and more confident. In some circuits, the capacitor remains in the circuit during operation, improving the power factor and efficiency of the motor; such motors are called capacitor.
| Circuit element | Function | Fault symptom | Influence on startup |
|---|---|---|---|
| Working winding | Main rotation of the rotor | Break or interturn short circuit | Motor does not hum, no reaction |
| Starting winding | Creating a starting torque | Wire break | Humming, but no rotation |
| Starting relay | Starting switching windings | Sticking or lack of contact | No starting or constant operation of the starter |
| Thermal relay | Overheat protection | Frequent shutdown | Cyclic startup attempts |
Diagnostics of the windings is carried out using a multimeter in resistance measurement mode. The normal resistance of the working winding is usually 10-20 Ohms, and the starting winding is 20-50 Ohms, although the exact values depend on the power of the motor and the model, for example, they may vary. If the resistance tends to infinity, there is a break; if it approaches zero, there is a short circuit. Whirlpool or Beko they may vary. If the resistance tends to infinity, there is a break; if it approaches zero, there is a short circuit.
Protective mechanisms and thermal relays
The starting process is stress for the electric motor, accompanied by high starting currents, which can be 5-7 times higher than the rated operating current. To prevent winding burnout and fire, the circuit includes thermal protection relay. It is often structurally combined with a starting relay in one housing, but performs the opposite function - it opens the circuit in case of danger.
The operating principle of a thermal relay is based on the properties of a bimetallic plate. When current flows, the plate heats up and bends. In normal mode, the bending is not sufficient to break the contacts. However, if the compressor cannot start for a long time (the mechanics are jammed, low voltage in the network) or operates with an overload, the current increases, the plate bends strongly and opens the power circuit.
☑️ Checking the protection system
After cooling (usually it takes from 5 to 20 minutes), the bimetallic plate returns to its original position, and the circuit closes again, allowing the compressor to try to start again. If you observe the cycle: “buzz for 5-10 seconds -> click -> silence for 10 minutes -> repeat”, this is a sure sign that the thermal protection is triggered.
⚠️ Attention: Frequent activation of the thermal relay (“clocking”) kills the compressor. Each such cycle is an attempt to turn on a jammed mechanism or start at unacceptable pressure in the system. Do not allow long-term operation in this mode.
Features of starting inverter compressors
Modern refrigerators are increasingly using inverter compressors, the operating principle of which is fundamentally different from the linear models described above. There is no strict connection to the 50 Hz network frequency and no on-off cycles. The motor turns on once at the first start after defrosting or a long period of inactivity and then only changes the rotation speed.
The start of such an engine is controlled by a special electronic unit - an inverter. It converts the alternating current of the network into direct current, and then again into alternating current, but with a smoothly variable frequency. This avoids huge inrush currents and mechanical shocks. The rotor begins to rotate gently, without the jerk and “sobping” sound characteristic of old refrigerators.
The absence of a starting relay and capacitor in the usual form makes the system more reliable, but more difficult to diagnose. If an inverter refrigerator Haier or Atlant does not turn on, the problem most often lies in the inverter module itself or in the stator windings, which in such motors are made according to a special three-phase circuit. Checking with a conventional multimeter here often does not give a complete picture, requiring specialized equipment.
Typical startup problems and their causes
Knowing how a working compressor should turn on allows you to quickly identify a breakdown. The most common situation is that the refrigerator hums, but does not start. This indicates that the electrical circuit is closed, current flows to the windings, but no mechanical rotation occurs. The reasons may be low voltage, a faulty start relay, or, worst of all, a jammed piston group.
Another option is a complete lack of response. You open the door, time passes, but there is silence. In this case, the circuit does not close. The culprits may be: a burnt-out thermostat, broken wiring, a malfunction in the control module (if it is electronic) or a burnt-out motor winding. It is also worth checking the integrity of the supply cable and plug.
A critical sign is a burning smell or a melted housing of the start relay. This indicates that the startup process was not going well, the contacts were sparking, and the temperature inside the compressor casing reached critical values. Operation of such a refrigerator is prohibited until the cause is eliminated, as there is a high risk of fire.
Sometimes a situation occurs when the compressor starts, runs for a few seconds and turns off with a click. This is the work of a thermal protection relay. Reasons: faulty starting winding, defective starting relay (does not turn off the starting winding, the motor overheats) or mechanical obstruction to shaft rotation.
Frequently asked questions (FAQ)
How long should the compressor run after turning on?
The operating time depends on the refrigerator load, the room temperature and the installed cooling power. Typically, the operating cycle ranges from 10 to 30 minutes, followed by a pause of approximately the same duration. In hot weather or during the first load, the operating time can be significantly longer.
Why can’t the refrigerator be turned on immediately after being turned off from the network?
After stopping, the pressure drop in the system remains: in the condenser it is high, in the evaporator it is low. The engine will not be able to turn the pistons against this pressure. It is necessary to wait 5-10 minutes for the pressures through the capillary tube to equalize, otherwise the thermal protection will work or the starting relay will burn out.
Is it possible to replace the starting relay with an analogue from another brand?
Yes, it is possible if the electrical characteristics (motor power, type of windings) and the geometric dimensions of the seat match. Often relays from Danfoss are suitable for many European and Asian models, but it is better to select them according to the catalog number or parameters of a particular compressor.
Is it dangerous if the compressor turns on too often?
Yes, it is dangerous. Frequent starts (less than 5-7 minutes of inactivity) do not allow the oil to return to the compressor crankcase, which leads to dry operation and rapid wear of the rubbing pairs. This also overloads the starting equipment. You need to look for the reason: a freon leak, loose doors closing or a malfunction of the thermostat.