The moment when you hear a quiet click, and then the increasing hum of the motor, is the culmination of a complex engineering process inside your household device. This is exactly how it begins cooling cycle, without which it is impossible to maintain food freshness. Understanding exactly how the compressor starts allows you not only to gain a deeper understanding of the equipment, but also to independently diagnose many common breakdowns.
The work is based on an electric motor, which drives a piston group that pumps the refrigerant. However, simply applying voltage to the windings is not enough - the motor requires a significant impulse to take off and overcome the inertia of rest. This process takes a fraction of a second, but it is at this moment that critical changes occur in the electrical circuit, which determine the further operation of the entire system.
It is important for the user to know that a proper start-up is always accompanied by a characteristic sound pattern and time intervals. If you notice that the refrigerator hums but does not start, or the clicks are repeated with alarming frequency, this is a direct indication of a failure in the primary circuit. Let us analyze in detail which components are responsible for this stage.
The role of the start-up relay in the switching circuit
The heart of the starting system is start-protective relay, which is mounted directly on the compressor housing. This compact device combines two vital functions: it supplies increased voltage to the starting winding at the time of start and protects the engine from overheating and short circuits. Without this element, the motor would not be able to overcome the initial resistance.
Inside the relay body there is an inductance coil through which the current of the main winding of the motor passes. When the refrigerator is turned off, the contacts are open. When power is applied, current rushes through the coil, creating a magnetic field that draws in the core and closes the contacts of the starting circuit. This allows the current to take the path of least resistance through start winding, creating the necessary torque.
Once the motor rotor reaches about 75-80% of the rated rotation speed, the current in the main winding drops to the operating value. The magnetic field weakens, and under the influence of gravity (or a spring), the core returns to its original position, opening the starting winding circuit. Further operation of the motor occurs only on the working winding.
⚠️ Attention: If the relay makes frequent clicks (every 10-20 seconds) and the compressor hums but does not start, immediately disconnect the device from the network. Long-term operation in this mode burns the motor winding in a matter of minutes.
There are also electronic relays where a posistor (thermistor) is used instead of a mechanical core. When voltage is applied, its resistance increases sharply due to heating, essentially breaking the starting winding circuit. Such systems are considered more reliable, since they do not have moving mechanical parts subject to wear.
Physics of the process: working and starting windings
The electric motor of the refrigeration unit is asynchronous and single-phase. The peculiarity of such motors is that to create a rotating magnetic field they need two windings shifted relative to each other by 90 degrees. One of them, working winding, has a thicker wire and a larger number of turns, which ensures stabilization of work in normal mode.
The second winding, called the starting winding, is made of a thinner wire and has a smaller number of turns. Its task is to create the initial impulse of rotation of the rotor. It is important to understand that the starting winding is not designed for long-term operation. If the circuit does not break after the start, the current in it will increase to critical values, which will lead to thermal destruction of the insulation.
The difference in resistance between the windings is a key parameter in diagnostics. In a working motor, the resistance of the working winding is usually 10-20 Ohms, while the starting winding is much higher, in the range of 30-50 Ohms (values may vary depending on the power of the motor). Checking these values with a multimeter is the first step when troubleshooting.
Why do the windings not burn out when starting?
Current flows through the starting winding for a very short time (less than 1-2 seconds). During this period, heat does not have time to accumulate in sufficient quantities to damage the insulation of the wire, even if the current exceeds the rated current.
Some modern models use capacitor starting. In this case, it is included in the starting winding circuit starting capacitor. It creates a phase shift in the current, which significantly increases the starting torque. This allows you to start more powerful compressors used in No Frost systems, where it is necessary to overcome high pressure in the circuit immediately after stopping.
The influence of temperature and pressure on engine starting
Starting a compressor is not only an electrical process, but also a mechanical overcoming of pressure in the system. When the refrigerator stops, the pressure in the refrigerant circuit is equalized, but complete equilibrium does not occur immediately. If you turn on the device immediately after turning it off, it will be extremely difficult for the motor to turn the piston against the residual freon pressure.
That is why modern refrigerators have a turn-on delay. The electronic control module or timer counts a few minutes (usually 3 to 10 minutes) before applying voltage to the compressor. During this time, the pressure in the system has time to stabilize, which makes starting easier and extends the engine life.
Low temperatures also affect the viscosity of the oil in the compressor crankcase. In winter, if the refrigerator was in an unheated room, the oil becomes thick. This creates additional resistance to the movement of rubbing parts. In such cases, the first start may be difficult, and the relay may not operate the first time.
| Parameter | Normal value | Influence on start |
|---|---|---|
| Network voltage | 220-230 B | If it drops below 190 V, the starting torque may not be enough |
| Resistance of the starting winding | 30-50 Ohm | A break (infinity) will prevent the motor from starting |
| Operating time of the starting relay | 0.5 - 2 sec | Longer - risk of overheating, less - under-rotation of the rotor |
| Circuit pressure | Equalizes in 3-5 minutes | High pressure requires more starting torque |
It is worth considering that in hot weather, when the condenser (radiator at the back of the refrigerator) is contaminated with dust, the condensation pressure increases. The compressor has to work under increased load, which can also affect the ease of its restarts after short rest cycles.
Diagnostics of startup circuit faults
If the refrigerator has stopped cooling, and the motor is silent or makes strange sounds, it is necessary to carry out an initial diagnosis. The first step is to check the presence of voltage in the outlet and the integrity of the power cord. If everything is in order with the external power supply, the problem lies inside the motor control circuit.
The most common malfunction is the failure of the starting relay. This can be determined by the characteristic crackling sound or absence of a click when turned on. A visual inspection may reveal a melted case or blackened contacts. Also, the thermal relay (protection against overheating) often burns out, breaking the power circuit completely.
To check the windings, you will need a multimeter. It is necessary to remove the back cover of the compressor, disconnect the relay and ring the contacts. Continuity will show whether there is an open circuit or a short to the housing. If the device shows infinite resistance on any of the windings, the motor is most likely faulty.
- 🔍 Sympath 1: Click, buzz for 5-10 seconds, then silence and click again after a minute - the piston group is probably jammed or the relay is faulty.
- 🔍 Symptom 2: Complete absence of sounds and reaction to switching on - the thermal relay has burned out or there is an open circuit in the power circuit.
- 🔍 Symptom 3: There is a hum, but there is no startup, the relay does not click - a problem with the starting winding or capacitor (if any).
- 🔍 Symptom 4: The motor starts, but quickly turns off with a characteristic click - the winding is overheating or the voltage in the network is low.
⚠️ Attention: When checking with a multimeter, be sure to disconnect the refrigerator from the power supply! Continuity of live circuits will lead to burnout of the tester and can be life-threatening.
The situation when the compressor starts jerkily deserves special attention. This may indicate an interturn short circuit in the windings. The engine tries to start, the current increases sharply, the protection is triggered, and the cycle repeats. Operating equipment in this mode is unacceptable.
Problems with capacitors and their replacement
In circuits with capacitor starting, it is this element that takes the brunt of the start. The capacitor accumulates charge and transfers it to the starting winding, creating the necessary phase shift. Over time, the electrolyte inside the capacitor dries out, the capacity drops, and the motor stops gaining the required speed to open the starting circuit.
Visually, a faulty capacitor often looks swollen or has traces of electrolyte leaks on the body. However, even an apparently intact element may have a critical capacity deviation. The check is carried out with a special device - an LC meter, or by replacing it with a known good analogue.
When replacing, it is important to observe the polarity (if the capacitor is polar) and the rated voltage. Using a capacitor with a lower operating voltage will lead to its rapid failure and possible explosion. Typically, elements with a voltage of at least 250-450 V are used.
☑️ Actions when replacing the start relay
It is worth noting that in some models the capacitor is combined with the relay in a single unit. In such cases, the entire assembly must be replaced. Attempts to disassemble a sealed unit and replace only the capacitor inside often lead to broken contacts and unstable operation.
When you need to call a specialist: critical situations
Despite the possibility of self-diagnosis of some components, there are situations when professional intervention is inevitable. If after replacing the relay and checking the windings the compressor does not start, the problem may lie in the very “heart” of the unit. Opening the compressor at home is impossible and impractical.
A technician will also be required if a refrigerant leak is detected. Often the compressor cannot start or is overloaded due to lack of proper pressure in the system. Attempts to “revive” the engine in such conditions will only finish it off. The system must be evacuated and refilled with freon.
A particular danger is the breakdown of the winding insulation on the housing. This is manifested not only by failure of operation, but also by the appearance of voltage on the metal parts of the refrigerator. Operation of such a device is deadly and requires immediate shutdown and repair.
In addition, modern inverter refrigerators have complex control electronics. Diagnosing their inrush currents and signals requires an oscilloscope and special knowledge. An attempt to check the windings of an inverter compressor with a conventional multimeter often gives false results due to the specific design of the motor.
Why does the compressor not start immediately after turning off?
This is normal operation of the protection system. The pressure in the circuit should equalize. If you start the motor against high pressure, the starting torque may be insufficient, which will lead to burnout of the windings or breakage of the valves. The delay timer prevents this.
Is it possible to start a compressor without a relay?
Theoretically, it is possible by using a button to briefly apply voltage to the starting winding, but this is extremely dangerous and requires qualifications. Without a protection relay, the motor can burn out in seconds if it seizes or experiences a power surge. It is not recommended to do this without a relay.
A buzz without starting is always a breakdown?
Not always. A short hum (up to 1 second) before starting is normal. If the hum lasts several seconds and repeats, this is a sign of a malfunction of the relay, windings or mechanical jamming of the piston group.
Does the temperature in the room affect startup?
Yes, indirectly. In a very cold room, the oil thickens, increasing resistance. In very hot conditions, the condensation pressure increases. Both factors increase the load on the engine at the time of start, requiring proper operation of the automatic starting system.