Sudden silence in the kitchen, where the refrigerator was habitually humming, or, conversely, loud clicks without subsequent starting of the motor, is always an alarm signal for the owner. Most often, these symptoms hide a malfunction of the start-up relay, which is a critical component in the cooling system. This small black or gray plastic block, attached to the side of the compressor, is responsible for starting the engine and protecting its windings from overloads.
When starting relay fails, the compressor either does not start at all, or operates in short bursts, after which thermal protection is triggered. Understanding why this happens helps not only to replace the part, but also to prevent the expensive unit from breaking down again. In this article, we will take a detailed look at the physical and electrical causes of the destruction of this component.
Design and principle of operation of the starting device
To understand the reasons for the breakdown, it is necessary to briefly consider the internal structure of the relay. Most modern household refrigerators use posistor or electromagnetic relays. A posistor is a ceramic element whose resistance increases sharply when heated. When the refrigerator is turned on, a current passes through it, it heats up and opens the circuit of the starting winding, leaving only the main winding to work.
Electromagnetic models operate on the principle of a solenoid: the current draws in the core, which closes the contacts of the starting winding, and after a set of revolutions it opens their Mechanical wear moving parts and thermal load on the contacts are the two main enemies of any design. Any part has its own resource of on and off cycles.
On the side of the compressor, the relay is attached to three pins coming from the motor. It is through these contacts that the high starting current is transmitted. If the contacts inside the plastic case oxidize or burn, the resistance in the circuit increases, which leads to local overheating and eventual melting of the case or destruction of the internal filling.
⚠️ Attention: There may be residual voltage or charge in the capacitors inside the relay (if they are in the control circuit), so before dismantling, make sure that the refrigerator is completely disconnected from the network for at least 10-15 minutes.
Power surges and electrical overloads
One of the most common reasons why a relay in a refrigerator breaks is instability of the electrical network. Power surges, which often occur in rural areas or in older apartment buildings, create extreme conditions for electronics to operate. When the mains voltage drops, the current in the motor windings increases to compensate for the loss of power, which leads to overheating of the relay contacts.
High-voltage pulses can break through the insulation inside trigger mechanismcausing a short circuit between the contacts. At this moment, a powerful electrical discharge (arc) occurs, which burns the metal of the contacts. After such an event, the relay ceases to perform its switching function, and the compressor hums, but does not start.
Frequent power outages are also harmful. Each “on-off” cycle is stressful for the posistor. If the light blinks constantly, the ceramic element does not have time to cool down or, on the contrary, experiences a thermal shock, which leads to the formation of microcracks in the structure of the material.
To protect expensive equipment in such conditions Engineers recommend use voltage stabilizers. They level out the input current and cut off dangerous peaks, prolonging the life of not only the relay, but also the compressor itself.
Thermal degradation and overheating of the compressor
The relay is located in close proximity to the compressor, which heats up to high temperatures during operation. If the ventilation system of the refrigerator is broken or the unit is standing close to the wall, heat transfer deteriorates. Constant overheating causes the plastic elements of the relay body to become brittle and lose their geometric shape.
Inside thermal relay (the protective part) there is a bimetallic plate. With prolonged overheating, it can lose its elastic properties - this phenomenon is called “metal fatigue”. The plate stops opening the contacts in time when overloaded, which can lead to burnout of the motor windings.
It is also worth considering the condition of the motor itself. If the compressor is worn and hard to crank, it will draw more starting current. The relay is forced to pass through itself a current exceeding the rated one, which causes intense sparking of the contacts and their rapid burnout.
Vibration and mechanical damage
The refrigerator is a vibrating unit. During operation, the compressor creates vibrations that are transmitted to all fixed components. The starting relay is mounted directly on the compressor terminals, taking on the main vibration load. Over time, this leads to weakening of the internal contacts and failure of the soldering of elements on the board (if the relay is electronic).
In older models with electromagnetic starting, vibration can cause rattling of the core. This leads to the fact that the contacts do not fit tightly together and begin to spark and burn. Visually, such a relay may look intact, but inside the contacts will be covered with a layer of carbon deposits.
Mechanical damage is also possible during transportation or careless maintenance. If, when trying to defrost the refrigerator or move it away for cleaning, a blow is struck to the back wall near the motor, the fragile ceramics of the posistor may crack.
| Type of damage | Symptoms | Probable cause | Consequences |
|---|---|---|---|
| Burning of contacts | The refrigerator hums, but does not start | Power surges, wear | No start of the compressor |
| Cracked posistor | Clicks, no buzzing | Mechanical shock, thermal shock | Break start circuit |
| Weakening of the spring | The compressor runs jerkily | Overheating, aging metal | Starting winding does not open |
| Case melting | Burning smell, visible deformation | Short circuit, overheating | Complete failure node |
The influence of moisture and corrosion
The kitchen is a room with high humidity, especially if there is a sink or stove nearby. Condensation that forms on cold surfaces or during defrosting may enter the technical openings in the rear panel. Moisture penetrating inside the relay causes oxidation of the metal contacts.
Oxides create high contact resistance. Current has difficulty passing through the oxidized layer, causing heating. This process is of an avalanche nature: the stronger the heating, the more active the oxidation occurs, until the contact completely disappears or breakdown occurs.
Corrosion can also affect the compressor terminals themselves, onto which the relay is placed. If the pins are covered with rust or oxide, the contact between them and the relay terminals will be poor, which will lead to local overheating and melting of the seats.
Is it possible to dry a wet relay?
Theoretically, if the water ingress was recent, you can try to thoroughly dry the relay with a hairdryer at low temperature for 30-40 minutes. However, there is no guarantee of performance, since water could have already caused corrosion inside the case.
Factory defects and low quality parts
Do not discount the human factor and production quality. In pursuit of cheaper designs, some manufacturers use low quality materials. The plastic of the case may not withstand the stated temperatures, and the contacts may be made of an alloy with a low silver content, which accelerates their fading.
Defects during assembly also occur when the contacts are not initially fully closed or the posistor has hidden defects. Such a part may fail after several months or even weeks of active use.
When replacing, it is important to select a relay with similar characteristics. Installing a part from another manufacturer or model of refrigerator, even if it physically fits in size, can lead to incorrect operation of the starting system.
☑️ Diagnostics before purchasing a new relay
Fault symptoms and diagnostic methods
How to understand that the problem is in the relay, and not in compressor? The first sign is a characteristic sound. A working refrigerator makes a quiet hum. If you hear a loud click, followed by a hum lasting 3-5 seconds, and then again a click and silence, this is a classic symptom of a faulty starter or a jammed compressor.
The second sign is the lack of cold when the light is on in the chamber. The compressor may not make any sound at all, or only a quiet hum will be heard without vibration of the housing. In some cases, the relay may click with a high frequency (crackling).
For accurate diagnostics, it is necessary to remove the relay. It is usually held in place by latches or screws. Remove the protective cover and disconnect the connector. Shake the relay near your ear: if a ringing or knocking sound is heard inside, it means that the posistor has crumbled or the core has come off, and the part definitely requires replacement.
⚠️ Attention: If, after replacing the relay with a new one, the refrigerator continues to behave the same (clicks and does not start), there is a high probability that the compressor itself is faulty (interturn short circuit or wedge). Further attempts to start may finally finish off the motor.
Replacement rules and precautions
Replacing a relay is a procedure available to a home handyman, but requires compliance with safety precautions. The main rule: all work is carried out only with the refrigerator completely disconnected from the network. It is necessary to unplug the cord from the outlet.
When installing a new part, it is important to orient it correctly. The housing usually has a mark UP (top) or an arrow indicating the correct position. If you install the relay upside down, the mechanism will not work and the compressor will burn out.
You should also check the condition of the contacts on the compressor itself. They must be clean and dry. If there are oxides on them, carefully clean them with fine sandpaper before putting on a new relay.
Is it possible to repair an old relay, or only change?
In 95% of cases, the relay must only be replaced. Internal elements (posistor, springs) are not repairable under domestic conditions. Attempts to clean the contacts or glue the body together give a temporary effect and are dangerous due to fire.
Why does a new relay burn out after a week?
This indicates a problem not in the relay, but in the system. Either the compressor is faulty (takes too much current), or there are constant voltage surges in the network, or the relay model is incorrectly selected (does not match the power or type).
Where can I find markings for purchasing an analogue?
The marking is applied to the side or top edge of the plastic case. Look for the model code (e.g. PTMRS, 305 etc.) and voltage. It is best to remove the old relay and search by its code or bring it to the store.
Is it dangerous to operate a refrigerator with a faulty relay?
Yes, it is dangerous. In addition to the lack of cold and food spoilage, there is a risk of overheating of the wiring, melting of the insulation and fire. In addition, frequent attempts to start “kill” the windings of the compressor, the repair of which is much more expensive than replacing the relay.