Many owners of household appliances notice strange sounds that the unit makes immediately after the compressor stops working. Instead of the expected silence, a dull knock, crackling or even the clink of metal is heard. This phenomenon often causes alarm, because we are accustomed to thinking that a working machine should make noise, and a resting machine should be silent.
However, the physics of the processes inside the cooling circuit dictates its own rules. Sharp change in pressure in the system, the movement of refrigerant through the tubes and the inertia of the moving parts of the motor can create sound effects of varying intensity. In most cases, this is a normal situation that does not require the intervention of a specialist.
However, loud and repetitive sounds should not be ignored. Understanding the nature of these noises will help you distinguish normal operation from signs of serious failure. In this article we will analyze in detail the mechanics of the occurrence of sounds when stopping the cooling cycle.
Physics of the process: why noise occurs exactly after stopping
At the moment when the thermostat gives the command to stop the engine, the pressure in the cooling system is at its peak. In the discharge line it is high, and in the suction line it is low. After turning off the power, the valves close, but pressure difference between different sections of the circuit is maintained.
The refrigerant under pressure begins to flow from the high pressure zone to the low pressure zone. This movement causes vibration of the tubes and a characteristic gurgling sound. If there are areas in the system where freon changes its state of aggregation, the sound may increase.
In addition, temperature compression of the metal plays a role. The condenser and evaporator tubes heat up and expand during operation, and contract when cooling. This process is accompanied by clicks, which are often confused with a mechanical knock.
⚠️ Attention: If a loud metallic clang is heard once and immediately after stopping the engine, this may be a sign of water hammer of liquid freon in the compressor cylinder.
It is important to distinguish the nature of the sound. Quiet flow of liquid is normal. A loud blow that shakes the body already requires attention. Modern compressors They often have thinner walls and are less soundproofed to save energy, which makes operating sounds more audible.
Why are old refrigerators quieter?
Old models ran on freon R12, which had different physical properties and lower operating pressure. Modern refrigerants R600a and R134a operate at different parameters, which changes the acoustics of the system.
Hydraulic hammer: the most common cause of loud knocking
One of the most common causes of a sharp sound is the so-called hydraulic hammer. Unlike water systems, where this phenomenon is destructive, in a refrigeration circuit it is most often safe, but noisy. The essence of the process is that the liquid fraction of the refrigerant enters the compressor cylinder at the time of starting or stopping.
When the motor stops, the piston freezes in a certain position. If at this moment liquid rather than gas flows into the cylinder, a sharp blow occurs. The metal of the piston hits the liquid, which is not compressed, unlike gas. This generates a dull knock.
The frequency of such knocks depends on the amount of refrigerant and the position of the refrigerator. If the unit was on its side during transportation, oil could flow into the evaporator circuit. When first started and subsequent cycles, it will cause noise.
- 🔊 A loud single knock immediately after the motor is turned off.
- 🔊 A series of clicks within 1-2 minutes after the cycle stops.
- 🔊 Vibration of the body at the moment of impact.
- 🔊 No knocking when the compressor is operating (noise only during transient processes).
Often this sound occurs if the refrigerator is installed at an angle. Violation of the geometry of the installation interferes with the correct outflow of oil and refrigerant. Tilt more than 2 degrees in any direction can provoke constant water hammer, which over time can damage the valve mechanism.
⚠️ Attention: If knocking becomes more frequent and the lack of cold is added to it, it is possible that the compressor has lost performance and cannot pump freon normally.
Residual pressure and refrigerant movement
After the compressor stops, the system does not freeze instantly. The pressure in the condenser (where the gas turns into liquid) remains high. In the evaporator (where the liquid boils) - low. The pressure equalization process can last from several seconds to a couple of minutes.
At this moment, the refrigerant actively flows through the tubes. If there are bends or constrictions in the system (capillary tube), the flow may create whistling or hissing sounds. This is a normal physical reaction of a mixture of gases and liquids.
This movement is especially noticeable in models with No Frost system. Where the air is forced to circulate, the sounds of freon flowing can resonate with the plastic elements of the air ducts, creating the illusion of a breakdown.
Sometimes users hear a sound similar to pouring sand. This may cause microbubbles to emerge from the refrigerant or oil solution, which collapse when the pressure changes. This sound is usually quiet and does not pose a threat.
Thermal expansion of body materials and tubes
Do not forget about the banal physics of solids. During operation, the internal components of the refrigerator heat up, and when stopped, they cool down. The temperature difference can be tens of degrees.
Metal tubes, aluminum evaporator plates and even the plastic housing of the inner chamber change their sizes. At the same time, they rub against each other or against the fastenings. This causes a characteristic cracking sound, reminiscent of clicks.
Most often such sounds are heard in refrigerators with a crying evaporator. Ice that builds up on the back wall makes “shooting” sounds when defrosting or simply when the temperature changes. This is absolutely normal.
- 🔊 The sound is similar to the crackling of plastic or thin metal.
- 🔊 It occurs not only when turned off, but also during operation.
- 🔊 The intensity depends on temperature changes in the room.
- 🔊 Often heard at night, when the house is quieter.
If your refrigerator is new, such sounds may be more pronounced. Over time, as the materials “grind in,” the noise may become less noticeable. However, a sharp increase in the crackling sound may indicate that some element has begun to come into contact with the vibrating tube.
Problems with shock absorption and fastening of the compressor
A compressor is an engine that vibrates during operation. To prevent this vibration from being transmitted to the body, it is suspended on springs or mounted on rubber feet. When the motor suddenly stops, inertia causes it to swing.
If shock absorbers they are worn out, dried out or burst, the compressor may hit the metal casing or frame of the refrigerator when it stops. This causes a loud clanging sound. Also, the cause may be loosening of the fastening bolts.
You can check this by gently pressing on the compressor (only when the refrigerator is unplugged!). If it moves too freely or, on the contrary, rests against the casing wall, then the alignment is disturbed.
| Type of malfunction | Nature of sound | When it occurs | Danger |
|---|---|---|---|
| Wear springs | Metal clanging | When the engine stops | Medium (destruction of tubes) |
| Loosening of bolts | Vibration and humming | Constantly | Low (noise) |
| Contact with casing | Metal ringing | When starting and stopping | High (break tubes) |
| Water hammer | Thud knock | Only when stopping | Low (if rare) |
To fix the problem, it is often enough to tighten the fasteners or replace the rubber bushings. In some cases, it is necessary to replace the entire compressor casing if it is deformed from constant impacts.
☑️ Diagnostics of compressor fasteners
The influence of installation level on acoustics
Correct installation of the refrigerator is the key to quiet operation. If the unit is not level, oil and refrigerant may accumulate in unintended areas of the circuit. When the compressor stops, this mass moves sharply, causing an impact.
In addition, the misalignment affects the operation of the motor itself. He has to work with increased load, which leads to overheating and a change in the nature of vibrations. You can check the level using a construction bubble level.
Adjustment is carried out by rotating the front support legs. The rear legs are usually non-adjustable. It is important to achieve a stable position so that the refrigerator does not wobble with a slight push.
⚠️ Attention: Do not use cardboard or wooden planks for leveling. Over time, they will wash out, and the distortion will increase, which will lead to new noise.
It is also worth checking whether the refrigerator is touching furniture or walls. Vibration during operation is transmitted to neighboring surfaces, which begin to resonate and hum. When turned off, this resonance fades, creating a specific sound trail.
When noise indicates a serious breakdown
Although most sounds are harmless, there are symptoms that cannot be ignored. If other signs of malfunction are added to the noise when turning off, diagnostics is required.
For example, if the refrigerator began to work longer, it became worse to freeze, and the sounds became metallic-ringing. This may indicate wear on the compressor shaft bearings or destruction of the internal motor mounting.
Another alarming signal is the appearance of a burning or oil smell. This indicates that friction inside the mechanism has increased, or depressurization has occurred. In such cases, operation is dangerous.
- 🔊 The knocking is accompanied by strong vibration of the entire cabinet.
- 🔊 The refrigerator has stopped reaching the desired temperature.
- 🔊 The compressor turns on and off too often (clocking).
- 🔊 There is a smell of burnt insulation or oil.
In such cases, independent repair is impossible. You need to call a technician to measure the pressure in the system and check the electrical parameters of the motor. Delay can lead to complete failure of the unit.
Prevention and methods for eliminating noise
To minimize the risk of loud sounds, monitor the condition of the refrigerator. Defrost it regularly unless you have a No Frost system. Keep the back of the condenser clean - dust causes overheating and changes in operating mode.
Check that the food inside does not touch the back wall, as this increases the transmission of vibration and sounds. Do not place foreign objects on the refrigerator that may rattle.
If you have just moved the refrigerator, let it stand upright for at least 4-6 hours before turning it on. This will allow the oil to drain into the compressor crankcase and prevent water hammer during the first start.
In conclusion, it is worth noting that absolute silence is not typical for a refrigerator. This is a complex mechanism in which physical and chemical processes constantly occur. The main thing is to be able to distinguish a working hum from a distress signal.
Is it normal for a refrigerator to crack like plastic?
Yes, this is normal. The plastic elements of the inner chamber and outer casing expand and contract when the temperature changes, producing a cracking sound. This happens especially often in new models or after defrosting.
Can a knock when turning off lead to a breakdown?
Single knocks (water hammer) are usually safe. However, if the impacts occur constantly and very loudly, this can lead to microcracks in the soldering of the tubes or destruction of the compressor valves in the long term.
Why does an old refrigerator hum less than a new one?
Older models had thicker case walls, heavier compressors and used different types of refrigerants. Modern requirements for energy efficiency and environmental friendliness dictate the use of lighter materials and other gases, which changes the acoustics.
What to do if knocking appears after transportation?
Most likely, oil has entered the circuit. It is necessary to turn off the refrigerator, let it stand in an upright position for several hours (preferably a day) without turning it on, so that the oil flows back into the compressor.
How to check whether the compressor is touching the casing?
With the refrigerator unplugged, gently rock the compressor. It should spring back. If a metallic ringing is heard when rocking or metal-to-metal contact is visible, the springs need to be adjusted or the bushings replaced.