A sudden knocking sound in the refrigerator can disturb the peace of any owner, especially if the equipment has been operating silently for years. Periodic knocks, clicks or rhythmic tapping are often the first sign of an incipient malfunction that cannot be ignored. Ignoring these sounds can lead to more serious damage, requiring expensive intervention from a technician or a complete replacement of the unit.
However, you should not immediately panic and look for the phone number of a service center, since in many cases source of noise it is hidden in trivial things that do not require complex repairs. Understanding the physics of a refrigeration machine helps distinguish normal operation from a critical breakdown. In this article, we will analyze in detail the mechanics of the occurrence of knocking, diagnose the main components and determine when you can handle it yourself and when you need to call a specialist.
The first thing to do when extraneous sounds appear is to listen carefully to the nature of the noise and its frequency. It is important to determine whether the knocking is associated with turning the engine on or off, or whether it occurs at random times. Precise localization of sound (behind, below, inside the chamber or on the side) will be the key to finding the cause of the malfunction.
Physics of sounds: normal operation of the compressor and defrost system
Modern refrigerators, even the quietest models, cannot operate in absolute silence. The main source of sound is compressor, which is an electromechanical pump. When the engine starts or stops, the piston group experiences a sharp change in pressure, which can cause characteristic clicks or dull knocks transmitted through the housing.
If a knock occurs approximately once every 8-12 hours and is accompanied by the sounds of flowing fluid or hissing, this is most likely the system working No Frost or drip defrosting. During the defrosting process of the evaporator, the heated refrigerant sharply changes its state of aggregation, and the thermostatic valves make sounds similar to blows. This is a normal situation that does not require intervention.
- 🔊 A short click when turning the motor on/off is the norm for most relays.
- 🔊 Rhythmic knocking every few hours is a sign of the defrost timer working.
- 🔊 A dull thud in the rear - vibration of the pipes against the wall of the housing.
Particular attention should be paid to the sounds produced refrigerant. As freon circulates through the piping system, gurgling sounds may occur, which are sometimes perceived as light blows from the inside. If the refrigerator has recently been defrosted or rearranged, such sounds may be amplified due to uneven distribution of oil in the compressor.
⚠️ Attention: If periodic knocking is accompanied by continuous operation of the compressor without stopping to rest, this may indicate a freon leak or loss of compression properties.
It is important to distinguish between mechanical knocking and acoustic effects that arise due to the expansion of materials. The plastic interior shelves and metal casing may produce sounds resembling cracking or banging when there is a sudden change in temperature. This is especially often observed in models with a system Total No Frost, where temperature changes are sharper.
Mechanical reasons: vibration and unstable position
The most common and easily eliminated reason why the refrigerator knocks or hums is a violation of the installation rules. If the unit is not level, vibration from the running engine is transmitted to the floor and amplified by resonance. As a result, light objects inside or structural elements begin to rattle and hit each other.
Checking stability is the first step that needs to be performed. It is enough to slightly rock the refrigerator body: if it wobbles, it means that the support legs are not adjusted correctly or the floor has a significant slope. Vibration can cause the compressor or condenser tubes to touch the back wall of the cabinet, causing a ringing metallic knock.
To fix the problem, you need to pull out the refrigerator and inspect the space around it. Often the source of noise is forgotten bottles, cans or kitchen utensils standing in close proximity. The vibration of the floor from the operation of a powerful motor can cause these items to “jump” and hit the legs of the refrigerator.
- 🛠️ Check the horizontal installation using a building level.
- 🛠️ Make sure that the back wall of the refrigerator does not touch the kitchen wall.
- 🛠️ Inspect the space at the back for foreign objects.
If visually everything is in order, try tightening the adjusting screws on the front legs. This will compensate for uneven floors and ensure a tight fit of all supports. Sometimes it is useful to place special anti-vibration pads under the legs that dampen the transmission of sound waves.
☑️ Diagnostics of stability
Malfunctions of the start relay and electrical parts
If a knock is heard strictly when you try to start the engine, but the refrigerator itself does not turn on after that or immediately turns off, the problem lies in the start relay. This small component is responsible for providing a starting pulse to the compressor windings. When a relay fails, it makes a loud, distinct click, followed by silence.
Inside the relay there is a coil and contacts that can burn or stick over time. At the moment the voltage is applied, a startup attempt occurs, accompanied by a characteristic impact sound. If the protection system detects that the engine has not started, it de-energizes the circuit, and after a while the cycle repeats. This creates the effect of periodic tapping.
Replacing the start relay is one of the few operations that can be done with your own hands with minimal skills. However, before purchasing a new part, you need to make sure that the compressor itself is in good working order, since jammed motor it will give similar symptoms. Testing the windings with a tester will help eliminate the worst scenario.
| Symptom | Probable cause | Sound character | Actions |
|---|---|---|---|
| Click and silence | Faulty starting relay | Single loud click | Replacing the relay |
| Series of clicks | Starting attempt motor | Frequent crackling or knocking | Compressor diagnostics |
| Humming and knocking | Voltage problems | Low-frequency hum | Network check |
| Regular knocking | Timer operation | Mechanical click | Normal |
It is worth noting that in some models refrigerators Indesit or Ariston the design of the relay may differ, so when replacing it is important to choose an analogue with identical characteristics. An incorrectly selected part may not start the compressor or, worse, lead to its overheating.
Problems with the fan in No Frost systems
In refrigerators with the system No Frost the fan is responsible for circulating cold air. If a knocking sound is periodically heard in the refrigerator or freezer, similar to the impact of a plastic blade on a hard object, the cause is most likely due to icing of the fan. Ice builds up on the walls of the evaporator and begins to interfere with the rotation of the impeller.
When the fan blades touch ice, a rhythmic cracking or knocking sound is heard, which may appear and disappear. This depends on the defrosting cycle: during defrosting the ice melts and the noise disappears, but during subsequent freezing the build-up forms again. Often this problem occurs due to a loosely closed door or a malfunction of the defrost heating element.
How to check the fan without disassembling?
For a preliminary check, you can carefully open the freezer door (some models have a sensor that turns off the fan when opened, so you need to find and hold this sensor with your finger). If there is noise when the door is closed, but disappears when it is open (with the sensor clamped), the problem is in the airflow.
To eliminate the problem, you will need to completely defrost the refrigerator. It is necessary to turn off the device from the network, empty the chambers of food and leave the doors open for at least 24 hours. Only long-term defrosting will allow the ice to melt in hard-to-reach places where the fan is located.
- ❄️ Unplug the refrigerator from the outlet for a day.
- ❄️ Remove all food and shelves.
- ❄️ Leave the doors wide open.
If after defrosting the problem returns after a short time, it means the defrost cycle is broken. In this case, the defrost sensor, timer or heating element may have failed. Operating a refrigerator with inoperative defrosting will lead to complete fouling of the evaporator with ice and loss of cooling capacity.
Wear of shock absorbers and compressor mountings
The compressor in the refrigerator is mounted on a special frame using shock-absorbing springs or rubber washers. Over time, under the influence of constant vibration and temperature changes, the rubber dries out, cracks or completely collapses. As a result, the metal body of the motor begins to touch the frame or tubes, producing a loud metallic knock with each stroke.
You can diagnose this problem by carefully touching the body of the running refrigerator from behind. If you feel a strong vibration that radiates into your hand and hear a rattling sound, the shock absorbers most likely need to be replaced. Also, the cause may be weakening of the fastening nuts, which are unscrewed over time due to vibration.
⚠️ Attention: Trying to place homemade gaskets (wood, pieces of rubber) under a compressor running under voltage is dangerous. It is better to entrust this procedure to a professional or act extremely carefully, observing safety precautions.
In some cases, the knocking is caused not by the compressor itself, but by the copper tubes adjacent to it. If they are too close to each other or to the chassis, vibration causes them to hit the metal. Gently bending the tubes by hand (only when the refrigerator is cold and turned off!) can temporarily solve the problem.
To replace the shock absorbers, you will need to remove the compressor casing. New rubber parts are inexpensive, but their installation requires skill, since the compressor is quite heavy. It is important not to damage the sealed tubes when installing new fasteners.
When you need to call a technician: critical breakdowns
There are situations when periodic knocking is a harbinger of a serious breakdown requiring specialist intervention. If you notice that the refrigerator not only knocks, but has also stopped freezing, or a “coat” of ice has appeared on the back wall, repairing it yourself may be useless. A technician is needed to accurately diagnose the pressure in the system and the condition of the refrigerant.
A knocking sound accompanied by a burning smell or smoke should cause particular concern. This may indicate an interturn short circuit in the motor windings or overheating of the wiring. In such cases, you must immediately disconnect the device from the network and do not turn it on again until the technician arrives.
Also, the help of a professional will be required if the knocking noise comes from inside the sealed circuit. This may mean that air or moisture has entered the system, which leads to water hammer when freon circulates. Elimination of such a malfunction requires evacuation of the system and charging with new refrigerant.
- 🚑 The knocking is accompanied by a lack of cold.
- 🚑 A burning smell has appeared or smoke is visible.
- 🚑 The compressor works non-stop, heating up to high temperatures.
You should not skimp on diagnostics in case of complex breakdowns. An attempt by unqualified intervention in a sealed circuit or electrical circuit can lead to the final failure of the equipment when repairs become economically unfeasible.
Preventing noise and extending service life
In order for your refrigerator to operate quietly and for a long time, it is important to follow simple operating rules. Regular defrosting (even for No Frost systems, preventive shutdown once a year is recommended) helps to avoid ice accumulation on internal mechanisms. Cleaning the condenser from behind from dust also reduces the load on the compressor, making it run quieter.
Watch how you load the chambers with products. Heavy cans and bottles should not touch the walls or each other, otherwise they will create additional noise when vibrating. The use of plastic containers and organizers helps secure the contents and avoid rattling.
Periodically check the integrity of the sealing rubber on the doors. If the rubber band breaks or loses its elasticity, warm, moist air enters the chamber, which leads to increased ice formation and, as a result, fan noise. Replacing the seal in a timely manner is a cheap way to prevent problems.
Is it possible to lubricate the rubbing parts of a refrigerator with oil?
It is strictly forbidden to lubricate the moving parts of the refrigerator (fan bearings, pistons) with ordinary oil. It will freeze in low temperatures or ruin the plastic. Only special cold-resistant lubricants are suitable for lubrication, but in domestic conditions it is better to limit yourself to cleaning from ice.
Why does a new refrigerator knock more than an old one?
Modern models often operate at higher speeds to achieve energy efficiency, which can create more noise. In addition, new refrigerators use environmentally friendly refrigerants, which may be noisier to circulate. Usually, after a few months of operation, the equipment “breaks in” and the noise decreases.
Is knocking dangerous for the products inside?
Knock itself does not affect the quality of the products if the temperature inside the chamber remains normal. However, if the knocking noise is caused by a faulty cooling system, the temperature may rise, causing food to spoil. Monitor the thermometer readings.
How long can a refrigerator with a knocking compressor last?
If the knocking is caused by wear of the shock absorbers, the refrigerator can work for years. But if a valve or piston group knocks due to lack of oil or hydraulic shock, the compressor can burn out at any time - from several days to several months.