At the moment when you set the temperature above the current one in the chamber, a complex chain of physical and electrical processes occurs inside the unit, ensuring the beginning of the cooling cycle. Starting the motor-compressor is the most energy-consuming and critical stage of the entire system, requiring precise synchronization of mechanical and electrical components. Understanding how the refrigerator engine startsis necessary not only for general development, but also for competent diagnosis of malfunctions when the device stops cooling or makes strange sounds.
Unlike many other household appliances, the refrigeration unit cannot start instantly, since its “heart” is a piston compressor - experiences colossal refrigerant resistance. That is why the design includes special protective and triggering mechanisms that take on the main load in the first seconds. If one of the elements of this circuit fails, you will hear a characteristic click, followed by silence or humming without rotation of the shaft.
Modern models can use various starting technologies, but the classic circuit with an asynchronous motor and starting relay remains the most common in the mass segment. We will analyze in detail each stage of this process so that you can clearly understand the sequence of actions of the mechanisms.
Physics of start: refrigerant resistance and inertia
At rest, the pressure in the cooling system is equalized, but the piston group of the compressor is under static pressure of freon. In order to move the piston from a dead center and create the necessary pressure difference between the high and low pressure zones, significant force is required. Starting torque must be 3-5 times higher than the rated operating torque of the engine, which creates an extreme load on the electrical network and motor windings.
If electric current was supplied to the motor directly, without special devices, the current strength in the windings would increase to critical values, causing overheating and possible burning of the insulation in a split second. That is why the triggering circuit is designed in such a way as to briefly change the characteristics of the magnetic field, creating a rotating pulse. After the rotor reaches about 75% of the rated rotation speed, there is no need for additional assistance.
It is important to consider that residual pressure remains in the system, which does not disappear instantly after stopping. This is one of the reasons why inverter compressors they often start smoother - they do not depend on a rigid network frequency, but classic models rely on a sharp jump in energy to overcome inertia.
⚠️ Attention: Frequent switching on and off of the refrigerator (less than 5-7 minutes after stopping) can lead to breakdown compressor. The pressure in the system does not have time to equalize, and the motor is physically unable to turn the pistons, which causes the protection to trip or a mechanical knock.
Starting relay device: the heart of the starting system
The key element responsible for the start is the starting relay. In classic refrigerators, it is an electromagnetic device that automatically connects the starting winding of the engine at the moment of switching on and turns it off after gaining speed. Inside the relay body there is a coil through which the current of the main winding passes, and a movable core with contacts.
At the moment the voltage is applied, the current in the main winding increases sharply (starting current). The magnetic field of the relay coil becomes sufficient to retract the core and close the contacts of the starting circuit. Current begins to flow through the starting winding, creating the phase shift necessary to generate rotor torque. This process takes only a few seconds.
As soon as the motor rotor reaches the required speed, the current consumption of the main winding drops to the operating level. The magnetic field of the relay coil weakens, and under the influence of gravity (or a spring in some models), the core drops, opening the contacts of the starting winding. The motor continues to operate only on the main winding.
- 🔌 Electromagnetic relays: they operate due to magnetic induction created by the current of the main winding, they are reliable, but sensitive to voltage drops.
- 🔥 Thermal (posistor) relays: use the property of the posistor to heat up and lose conductivity, often combined with thermal protection, more compact.
- ⚙️ Combined devices: contain in one housing both a trigger mechanism and a thermal fuse that protects against overheating.
There are also models with solid-state starting devices (posistors), where the role of a switch is played by a ceramic element that changes its resistance when heated. Such devices do not have moving mechanical parts, which theoretically increases their service life, but they require time to cool down before the next start.
⚠️ Attention: When replacing a relay, be sure to check that it matches the engine markings. Installing a relay with an inappropriate operating current will either result in the engine not starting, or the starting winding will burn out due to the relay not turning it off in time.
Why does the relay click, but the refrigerator does not start?
If you hear a series of clicks, this means that the starting relay is trying to turn on the motor, the current increases, but the motor cannot move. After a few seconds, the thermal protection (bimetallic plate) is triggered and opens the circuit. After cooling, the protection closes and the cycle repeats. Reasons: jammed compressor, interturn short circuit or malfunction of the relay itself.
Electrical diagram: operation of the stator windings
The refrigeration compressor motor is asynchronous with a squirrel-cage rotor. The stator of such a motor has two windings: the main (working) and starting windings. They are shifted relative to each other by 90 electrical degrees. To create a rotating magnetic field, the current in these windings must also be shifted in phase.
The working winding is made of thicker wire and has less active resistance. It is designed for long-term operation and the creation of the main magnetic flux. The starting winding has a higher resistance and fewer turns (or is wound with a wire of smaller cross-section). It is through it that at the moment of start a current passes, creating the necessary initial rotation impulse.
In some circuits, to increase the starting torque, a capacitor is connected in series with the starting winding. This allows you to create a larger phase shift and, accordingly, a more powerful rotating force. However, most household refrigerators use a split-phase circuit, where the shift is provided by the difference in the inductive resistance of the windings.
Control over switching between the “start” and “run” modes is carried out through a terminal block located on the compressor housing. Three contacts are suitable for it: common, working (Run) and starting (Start). Correct connection of wires to these contacts is critical.
| Parameter | Working winding (Main) | Start winding |
|---|---|---|
| Resistance | Low (10-25 Ohm) | High (30-60 Ohm) |
| Wire cross-section | Thick | Thin |
| Operating time | Constantly | Only at start (1-3 sec) |
| Function | Maintaining rotation | Creating starting torque |
The role of thermal protection in the starting process
Thermal protection is the “safety rope” of the engine, preventing it combustion in emergency situations. It is a bimetallic plate that bends under the influence of temperature. In normal mode, the current passes through the plate without causing critical heating, and the contacts remain closed.
At the moment of starting, when the current in the windings is at its maximum, the plate also heats up, but the inertia of the system allows the engine to start before the protection has time to operate. However, if the start-up is unsuccessful (for example, the piston is jammed) or the voltage in the network drops, the current remains high for a long time. The plate heats up, bends and opens the power circuit, de-energizing the compressor.
After cooling (usually this takes from 2 to 10 minutes), the plate returns to its original position and the circuit is closed again. If the fault is not resolved, the cycle “attempt to start - heating - shutdown” will be repeated. This phenomenon is often called “cycling.”
There are also protections that respond directly to the temperature of the compressor housing, and not to the current strength. They are attached directly to the metal surface of the motor and open the circuit when a critical threshold is reached, usually around 135-140°C.
Starting algorithm: step-by-step sequence
The process of starting a refrigerator is a well-established algorithm that takes a fraction of a second, but is of critical importance. Let's take it step by step to understand where exactly the problem may be hiding if the refrigerator is humming but not cooling.
First, the thermostat or electronic control module closes the circuit, applying voltage to the compressor circuit. The current flows through the thermal protection (which is cold and closed at this moment) and through the start relay coil. Since the rotor is stationary, the resistance of the windings is minimal, and the current reaches peak values.
The magnetic field of the relay draws in the core, closing the contacts of the starting winding. The engine receives an impulse and begins to rotate. At the same time, the bimetallic thermal protection plate begins to heat up. After 1-3 seconds, the rotor reaches operating speed, the current drops, and the relay opens the starting circuit. The engine enters operating mode.
☑️ Diagnosis of starting problems
If a failure occurs at any stage, the system goes into emergency mode. For example, if the relay is stuck closed, the starting winding will burn out. If the relay does not close at all, the engine will only hum, trying to start until the thermal protection is triggered.
⚠️ Attention: Technical characteristics of compressors and relays may vary depending on the manufacturer (Danfoss, Secop, LG, Samsung). Always check the markings of parts with the documentation or the correspondence table before replacing.
Diagnosis of faults during startup
Understanding how the engine starts allows you to quickly diagnose a problem based on external signs. If you hear a quiet hum, which abruptly ends with a click, and repeats after a while, this is a classic symptom of a malfunction of the starting relay or thermal protection.
If a loud click is heard, the motor tries to jerk, but a metallic knock is heard and the hum subsides, there is a high probability of mechanical jamming of the compressor (“wedge”). In this case, the motor is physically unable to crank the crankshaft, the current increases instantly, and the protection emergency turns off the power.
If the motor starts, runs for a few seconds, and then turns off with a characteristic click, the problem may be in thermal protection, which falsely triggers due to aging of the bimetal, or in insufficient voltage in the network, due to which the engine cannot gain speed and continues to consume high current.
For accurate diagnostics, it is often necessary to measure the current consumption at the time of startup using current clamps. Normal starting current can be as high as 10-15 Amps, but it should briefly drop to 1-2 Amps immediately after starting. If the current remains high, look for the reason in the mechanics or windings.
Inverter technologies versus classics
In modern models, inverter compressors are increasingly found, the starting principle of which is radically different from the scheme described above. There is no classic starting relay or separation into starting/working winding in the traditional sense.
The inverter converts the alternating current of the network into direct current, and then again into alternating current, but with a variable frequency. Starting occurs at low frequencies (about 10-20 Hz), which allows the engine to smoothly gain speed without huge starting currents. This reduces the load on the network and mechanical parts.
The absence of a strict connection to the network frequency allows such engines to be more economical and quiet. However, diagnosing their malfunctions is more difficult and requires special equipment, since standard methods for testing the windings often do not provide a complete picture of the condition of the control electronics.
Despite progress, classic compressors remain more repairable in the absence of a service center, since replacing the start relay is a procedure accessible even to an amateur with a minimal set of tools.
Is it possible to start refrigerator without a starting relay?
Theoretically, if you manually apply voltage to the starting winding at the moment of switching on and remove it a second later, the motor will start. However, in practice this is extremely dangerous and impractical. Without a relay, the motor will operate on only one winding, which will lead to overheating, loss of power and eventual combustion. In addition, the risk of electric shock during such manipulations is very high.
Why may a new compressor not start?
The reasons may be incorrect connection of the windings (contacts are mixed up), a malfunction of the new starting relay (defective or incompatible), or contamination of the system (if proper evacuation and replacement of the filter-drier were not carried out during installation, moisture or debris could get into the compressor).
How long should the compressor cool down after an unsuccessful start?
The minimum cooling time of the thermal protection is 2-3 minutes, but to completely equalize the pressure in the system and cool the windings, it is recommended to pause for at least 10-15 minutes before trying to turn on again.