The situation when the refrigerator knocks when turned offis familiar to many owners of household appliances. This sharp, often frightening sound occurs when the motor-compressor stops working, and may be accompanied by vibration of the housing or a metallic clanging sound. For most users, this becomes a cause for concern, because the silence in the apartment is broken by a characteristic knock, which can be heard every 15-30 minutes depending on the operating cycle of the unit.
It is important to immediately note that this sound does not always indicate a breakdown. The design of a refrigeration machine is complex and includes many moving elements that are subject to thermal expansion and mechanical vibrations. Understanding the physical processes occurring inside compressor and tubes will help you distinguish normal operation from a critical malfunction that requires the intervention of a technician.
In this article we will analyze in detail the mechanics of knocking, analyze the operation start relay and thermostat, and also consider cases where noise indicates wear of parts. You will learn how to carry out initial diagnostics with your own hands and in what situations the operation of equipment becomes unsafe.
Physics of the process: why sounds occur when it stops
The main reason why the refrigerator makes a sound when turning off lies in the change in refrigerant pressure and inertia moving parts. When compressor operates, it pumps freon at high pressure into the condenser. At the moment of a power outage, the pressure in the system changes sharply, which causes water hammer or movement of liquid through tubes, which can hit the walls of the housing or each other.
In addition, we must not forget about the thermal expansion of materials. Internal elements, such as the evaporator and pipelines, cool down during operation, and when stopped they begin to warm up to room temperature. Metal and plastic compress and expand at different rates, which often leads to a characteristic crackling or clicking sound, which many confuse with knocking.
There are several key factors that influence the intensity of sound:
- 🔊 Water hammer: a sharp change in the flow of refrigerant in the tubes.
- 🌡️ Thermal deformation: compression of plastic and metal when temperature changes.
- ⚙️ Rotor inertia: stopping of the rotating parts of the engine with a characteristic damped hum.
If the sound resembles a soft pop or a quiet one The click is most likely the normal operation of the system. However, if you hear a loud metallic clang, as if a heavy object has fallen, you should take a closer look at the technical condition of the unit.
The role of the starting relay and electromagnetic processes
One of the most common reasons for a loud click at the moment of shutdown is the work start relay. This small but important element is responsible for starting the compressor engine and protecting it from overloads. Inside the relay there is a coil and a movable core, which, when voltage is applied, is retracted, closing the contacts, and when disconnected, falls back under the influence of gravity or a spring.
The sound of the relay core falling can be quite loud, especially in older models of refrigerators or in units installed on an uneven floor, where the resonance is enhanced vibration. In modern models with inverter compressors, this process is quieter, but there are also solenoid valves that produce characteristic sounds when changing operating modes.
⚠️ Attention: If the relay click is accompanied by a repeated attempt to turn on the motor (a series of clicks every few seconds), this may indicate a malfunction of the relay itself or the compressor windings. In this case, it is better to de-energize the equipment.
Relay diagnostics are often carried out visually and by ear. If the relay housing is cracked or blackened, it will need to be replaced. It is also worth checking the tightness of the relay on the compressor contacts - a loose fastening can increase the rattling.
Thermostat: source of characteristic clicks
Another “culprit” of noise is thermostat (thermostat). This mechanical device opens the electrical circuit when the temperature in the chamber reaches a set value. Inside the thermostat there is a sensitive membrane and contacts that, when opened, produce a distinct click. When the compressor is turned off, this sound may seem louder due to the general silence in the operation of the unit.
The intensity of the click depends on the design of the thermostat and the cooling rate of the capillary tube. If the refrigerator is old, the contacts inside the thermostat may have oxidized or burned, which increases the resistance and makes the sparking (and therefore the sound) more pronounced.
You can understand that it is the thermostat that is knocking by the nature of the sound: it is a short, loud click, often accompanied by a slight vibration response from the case. Unlike the knocking sound of a compressor, this sound does not come from the bottom of the unit, but usually from the top, where the control chamber is located.
Wear of shock absorbers and compressor mountings
The most serious mechanical cause of knocking is wear shock absorberson which the compressor is suspended. The refrigerator motor is not tightly screwed to the frame, but hangs on springs or rubber feet to dampen vibrations. Over time, the rubber dries out, cracks or completely collapses, and the metal part of the compressor begins to touch the frame or housing.
When the motor stops, when the rotor still continues to rotate by inertia, a beating occurs. If shock absorption is compromised, the compressor may hit metal components, producing a loud, unpleasant clanging sound. This is not only noisy, but also dangerous, since vibration can lead to broken pipes or depressurization of the system.
You can check the condition of the fasteners by slightly tilting the operating refrigerator (carefully!). If you feel a lot of chassis vibration or hear rattling, the problem is most likely with the suspension. In such cases, replacement of rubber washers or springs is required.
| Sound type | Probable cause | Danger | Actions |
|---|---|---|---|
| Thud | Rotor stop, inertia | Low | Observation |
| Audible click | Relay or thermostat | Low | Checking contacts |
| Metal clanging | Compressor touching frame | High | Replacing shock absorbers |
| Crackling and creaking | Thermal expansion | No | Normal |
The influence of installation level and level floor
Often users forget that correct installation of the refrigerator directly affects the noise level. If the unit is not level, the center of gravity shifts and the load on the compressor shock absorbers is distributed unevenly. When the engine stops, a misalignment occurs, and the heavy motor may hit the housing wall or frame.
To eliminate this problem, you need to level the refrigerator. Most models have adjustable feet on the front panel. They need to be unscrewed so that the refrigerator tilts slightly backwards (for proper closing of the doors) and stands steadily, without swaying with a slight push.
☑️ Diagnostics of refrigerator installation
It is also worth checking whether vibrating parts of the refrigerator (for example, the back grill or pipes) are not touching the cabinet walls or adjacent furniture. Even a light touch can increase the sound of the compressor stopping significantly, turning a quiet hum into a loud knock.
When a knock indicates a breakdown: critical symptoms
Although many sounds are normal, there are situations where a knock when shutting down is a harbinger of a serious breakdown. If you hear that after the shutdown click, an attempt to start is immediately followed, which ends again with a click, and so on several times in a row, this is a sign faulty start relay or problems with the compressor.
Another alarming symptom is the appearance of a knock that was not there before, in combination with deterioration in freezing quality. If the refrigerator stops freezing and begins to knock loudly with each cycle, a water hammer may have occurred due to a blockage in the capillary system or oil getting into the circuit.
⚠️ Attention: If the knocking is accompanied by a burning smell or smoke, immediately unplug the refrigerator! Operation of such a device can lead to a fire.
If the compressor operates “in a hurry” (hums very loudly) and makes a strong knock when turned off, this may indicate an imbalance in the internal mechanisms of the motor. Such a unit requires professional diagnostics and, probably, replacement of the compressor.
Is it possible to ignore a quiet knock?
If the knock is quiet, not accompanied by other symptoms (heating, lack of cold) and is heard only at the moment of shutdown, most likely this is thermal expansion or relay operation. However, if the sound increases over time, it is better to call a specialist for preventive maintenance.
Do-it-yourself methods for eliminating noise
If you determine that the knocking is caused by vibration or touching the tubes, you can try to fix the problem yourself. First, make sure all shipping bolts (if any) are removed. Then inspect the back of the refrigerator: the copper tubes should not touch each other or the body.
Carefully, trying not to bend the tubes too much (they may burst!), spread them so that the gap between them is at least a few millimeters. You can also place pieces of soft rubber or foam rubber in places where vibration is transmitted to the body.
If the problem is in the compressor shock absorbers, you will need to remove the back cover (after unplugging the refrigerator!). Inspect the rubber washers. If they are intact but dry, you can lubricate them with special silicone grease. If the rubber is damaged, replace them with new ones, choosing an analogue in size.
Prevention and proper care of equipment
To extend the life of the refrigerator and minimize noise, it is important to monitor its technical condition. Regularly, at least once every six months, move the unit away and wipe the back wall of dust. Dust on the condenser causes the compressor to work longer and harder, which accelerates wear of parts and increases vibration.
Also make sure that a “coat” of ice more than 5 mm thick does not form inside the chambers. Excess ice changes the thermal regime, causing the thermostat and compressor to operate in abnormal modes, which can provoke unnecessary sounds when switching cycles.
Following simple operating rules will help you avoid unpleasant surprises. If you doubt the nature of the sound or cannot find its source, it is better to trust professionals who will carry out diagnostics using special equipment.
Is it normal if the refrigerator knocks only at night?
Yes, this is normal. At night the apartment is quieter, and any sounds from equipment become more noticeable. In addition, the ambient temperature is often lower at night, which can slightly change the operation of the thermostat, making the clicks more distinct.
Can a new refrigerator knock?
In the first weeks of operation, a new refrigerator may make various sounds, including knocking. This occurs due to the grinding in of parts, final shrinkage of materials and adjustment of thermal conditions. If the knock is not metallic and is not accompanied by vibration, there is no need to worry.
How to distinguish the knock of a compressor from the noise of a fan?
The knock of a compressor is always tied to the on/off cycles (every 20-40 minutes). The noise of the fan (if it is in the No Frost model) is heard constantly while the motor is running, or turns on periodically regardless of the compressor stopping, and is more like the hum or cracking of the blades.
Does the amount of food in the refrigerator affect the knocking?
Indirectly - yes. A full refrigerator maintains its temperature better and the compressor turns on less often. An empty refrigerator heats up faster, operating cycles become more frequent, and, accordingly, you hear switching on and off sounds more often, including possible knocking.
What should you do if the knocking noise appears after defrosting?
If the knocking noise appears after defrosting, check whether drops of water have got on the electrical contacts or in the compressor area. Also make sure that you assemble all the shelves and drawers correctly - sometimes vibration is transmitted to loose elements inside the chamber, creating the illusion of a motor knocking.