The situation when the refrigerator knocks when turned offis one of the most common complaints of owners of household appliances. This sound is often described as a short metallic clang, thud, or sharp click that occurs as the motor-compressor completes its cycle and enters a resting state. For many users, such noise becomes a source of constant irritation, especially at night, when there is silence in the apartment.
It is important to immediately note that not every sound indicates a breakdown. Modern refrigerators equipped with complex compression systems, where the movement of the refrigerant and the operation of mechanical components inevitably create a certain acoustics. However, if the knocking has become louder, its character has changed or appeared abruptly, you should not ignore it. A sharp metal blow when the motor stops often indicates a problem with shock absorption or fastening of the compressor.
In this article we will analyze in detail the physics of the processes occurring inside the unit at the moment stops, and highlight the reasons that require the intervention of a specialist. Understanding the nature of sound will help you not to panic ahead of time or, conversely, to quickly respond to a serious malfunction, preventing expensive repairs.
Physics of the process: why a knock occurs when you stop
To understand the nature of the noise, you need to consider what is happening inside compressor at the moment of a power outage. The compressor is the heart of the refrigerator, operating under high pressure. When the thermostat or electronic module commands to stop, the current supply stops, but the inertia of the moving parts remains for another split second.
At this brief moment, a sharp change in pressure occurs in the piping system. The refrigerant, which was previously actively circulating, stops, and the effect of water hammer or simply a sharp redistribution of liquid and gas occurs. If the system is not perfectly secured, this impulse is transmitted to the housing.
It is also worth considering the thermal expansion of metals. During operation, the compressor and adjacent tubes heat up, and when turned off they begin to cool down. This process can cause characteristic clicks, which are sometimes perceived as knocking.
⚠️ Attention: If the knocking is accompanied by vibration of the entire body of the refrigerator, which is transmitted to the floor, this is a clear sign of imbalance of the unit or wear of the rubber supports.
A quiet, one-time click of the relay is considered normal or a soft humming noise that subsides gradually. Loud clangingresembling the fall of a metal object, already goes beyond the normal operation of a working device.
Main causes of a mechanical nature
The most common cause of knocking is physical wear or displacement of the fastening elements of the compressor itself. The motor is suspended on springs inside a metal casing to dampen vibrations. Over time, these springs can stretch, burst, or move out of place.
When the engine stops, when the force holding the rotor in a certain position disappears, the compressor housing can swing and hit the inner walls of the casing. This gives rise to that ringing metallic sound.
Another mechanical reason is the loosening of the bolts securing the compressor to the refrigerator frame. Vibration during operation gradually loosens the connections. At the moment of stopping, the metal parts hit each other.
- 🔨 Loosening the nuts: Fastening elements require periodic tightening, since vibration weakens the threaded connections.
- 🔩 Wear of springs: The suspension springs lose their elasticity or break, allowing the compressor to dangle.
- 🧊 Contact with tubes: Copper tubes of the cooling system can shift and, when the engine stops, hit the housing or each other.
- 🏗️ Frame deformation: In rare cases, the frame or suspension geometry could be damaged during transportation.
To diagnose mechanical problems, it is often necessary to remove the back cover of the refrigerator. However, if you do not have the skills to work with electrical appliances, it is better to entrust this to a specialist.
Hydraulic hammer and problems with the refrigerant
Another serious cause of knocking is the so-called hydraulic hammer. This phenomenon occurs when liquid refrigerant enters the compressor cylinder instead of gaseous freon. The liquid does not compress, which leads to a sharp impact of the piston group.
Most often this happens when the thermostatic valve is faulty or the system is not charged correctly. When the compressor is turned off, the pressure drops sharply, and residual liquid can cause knocking. This is dangerous for the durability of the motor.
It is also worth mentioning the oil. The compressor contains a special oil to lubricate the rubbing parts. If its level is insufficient or it has lost its properties, the noise during operation and stop increases.
| Sound type | Probable cause | Danger |
|---|---|---|
| Thud blow | Piston impact liquid | High |
| Metal clanging | Casing contact with casing | Medium |
| Crackling | Thermal expansion | Low |
| Spring ringing | Suspension rupture | Medium |
If you suspect water hammer, it is better to suspend operation of the refrigerator until the technician arrives, as this may lead to to compressor wedge.
The influence of installation level and vibrations
Often the cause of a banal knock lies not inside, but outside - in improper installation of the unit. The refrigerator must stand strictly horizontally. If one of the legs is twisted more strongly or the floor is uneven, the housing is warped.
In this position, the internal suspension of the compressor works with a warp. When the motor stops, the housing “falls” to the side and hits the walls. This creates the illusion of a breakdown, although technically the device is working properly.
☑️ Checking the installation of the refrigerator
To fix the problem, use a building level. Height adjustment is done by twisting or unscrewing the front support legs. Rear wheels usually serve only for transportation and should not bear the main load.
Also check that vibrating parts of the refrigerator (for example, the rear grill or tubes) are not touching the cabinet walls or other objects furniture. When turned off, residual vibration can be transmitted to these items, causing rattling.
⚠️ Attention: Never leave the transport bolts on the compressor if they were installed by the manufacturer to secure them during transport. They must be removed before turning on for the first time, otherwise knocking and breakdown are guaranteed.
Problems with the starting relay and electrical system
Sometimes a knock when turning off is confused with the sound of operation starting relay. Although a relay usually clicks when turned on, a faulty relay can also make strange noises when the circuit opens. This is due to sticking of contacts or mechanical wear of the core.
If the relay does not open the circuit instantly, a repeated short-term attempt to start may occur, which is accompanied by a shock. In modern models with inverter compressors, the electrical part is more complex, and diagnostics require special equipment.
Pay attention to the wiring. If the wires are too close to the compressor, vibration may cause them to hit the hot casing or other parts, creating a characteristic cracking or knocking sound as the vibration dies down.
Is it possible to replace the relay yourself?
Replacing the starting relay is a technically simple procedure, but requires precise selection of the model. An incorrect relay can burn out a compressor in a matter of minutes. If you are not sure about the markings, it is better to contact a specialist.
Diagnostics of the electrical part often begins with listening to the operation of the relay. If the clicks become too loud or double, this is a reason to replace the element.
Specifics of inverter and linear compressors
Owners of refrigerators LG, Samsung and other brands with linear or inverter compressors may encounter special types of noise. These devices operate on the principle of a reciprocating piston, rather than a rotating rotor.
When turned off, such compressors may make a sound similar to the sound of knuckles or clattering. This is due to the design of the magnetic drive. In most cases, this is a a standard featureinstalled by the engineers.
However, if the sound changes and begins to resemble blows, the plastic piston guides may have worn out. Unlike classic motors, there are fewer metal parts, but plastic ages over time.
Manufacturers often indicate in the instructions the permissible noise levels for such models. It is worth checking the documentation before calling a technician.
Self-diagnosis algorithm
Before calling the service center, try to carry out the initial diagnosis yourself. This will help you more accurately describe the problem to the technician or, perhaps, solve it without cost.
Listen first: does the refrigerator knock only when turned off or does the noise continue? Try to lightly press the compressor housing with your hand (be careful, it may be hot!) at the moment of switching off. If the knocking noise disappears, then the problem is in the depreciation.
Check the stability. Rock the refrigerator. If it wobbles, adjust the legs. Inspect the area around: there are no objects that can resonate.
- 👂 Localization: Open the door and listen to understand where the sound is coming from - from below (compressor) or from inside the chamber.
- 🖐️ Tactile method: Gently touch the tubes. If they tremble and hit the wall, they need to be carefully moved away.
- 📉 Observation: Track whether the knocking depends on the number of products in the chamber (loading affects the operating time and frequency of cycles).
If simple measures do not help, and the sound causes concern, do not delay calling a specialist. Timely repair always cheaper than replacing the compressor.
Why does an old refrigerator knock more than a new one?
Over time, the metal gets tired, the springs lose their elasticity, and the lubricant thickens. In addition, older models often used less effective soundproofing methods. Natural wear leads to an increase in gaps and, as a result, to louder knocks when the mechanisms stop.
Is it dangerous to ignore knocking when turning off?
If the knocking is caused by a broken fastening, over time this can lead to breakage of the tubes and leakage of freon. If the cause is water hammer, the compressor valves may fail. Therefore, it is not recommended to ignore sudden changes in the sound background.
Is it possible to lubricate the compressor so that it does not knock?
No, the compressor is a sealed unit. The lubricant circulates in it along with freon. Adding oil or attempting to lubricate external parts (other than the supports) is useless and may be harmful. If lubrication is required inside, the compressor must be changed or opened in a workshop.