The situation when the refrigerator suddenly stops cooling food, but continues to hum or, conversely, stands in deathly silence, often confuses the owner. In most cases, the culprit of this behavior is a small but critical element of the electrical circuit - starting relay. It is this component that is responsible for starting the compressor engine, which, in fact, is the heart of the entire cooling system. Without its correct operation, the motor will either not start at all, or will operate in emergency mode, quickly overheating.
Understanding exactly how the unit behaves when this unit fails, allows you not only to save on calling a technician, but also to prevent more expensive repairs, for example, replacing the compressor itself or the entire circulation system refrigerant. Thermal relay, which is often paired with a starter, performs a protective function, turning off the power during overloads. If this mechanism fails, the circuit opens incorrectly, which leads to chaotic switching on and off of the equipment.
In this article we will analyze in detail the physical processes occurring inside the refrigeration cabinet when the relay breaks down, describe the characteristic sounds and behavior of the indicators, and also provide an algorithm of actions for initial diagnosis. You'll learn why the engine may hum for a few seconds and then click, and what to do if you notice a burning smell. It is important to distinguish a relay malfunction from problems with the refrigerant or electronic control module.
Functional purpose of the starting and thermal relay
To understand the consequences of a breakdown, you need to clearly understand the operating principle of a working mechanism. The start relay is an electromechanical switch that supplies voltage to the start winding of the compressor motor only when it starts. As soon as the motor rotor reaches the required speed (usually this takes a fraction of a second), the relay opens the starting winding circuit, and the engine continues to operate on the main winding. This process is critical for creating the initial torque.
It often works in parallel with the starting one thermal relay (thermal protection). Its job is to control the amount of current passing through the motor. If the current exceeds the norm (for example, due to jamming of the piston group or problems with the voltage in the network), the bimetallic plate inside the relay heats up and bends, opening the contacts and de-energizing the compressor. After cooling, the plate returns to its original position and the cycle can be repeated. This protects the motor windings from combustion.
- 🔌 Startup initiation: Applying a short-term pulse to the starting winding to shift the phase and start rotating the rotor.
- 🛡️ Overload protection: Instant power off during current surges or overheating motor, preventing fire and equipment failure.
- ⏱️ Time delay: Providing a pause before restarting (usually 3-5 minutes), necessary to equalize the pressure in the system.
Structural these elements can be combined into one housing or made separately, depending on the model of the refrigerator. In modern inverter models, the relay functions are performed by an electronic control board, but in classic compressor refrigerators (and most of them) it is mechanics that are used. POSISTOR is a modern analogue of a mechanical starting relay, working on the principle of changing resistance when heated, but the principle of its failure is similar to the classic one.
Symptoms of a malfunction: how the equipment behaves
When the relay fails, the refrigerator begins to behave uncharacteristically. The most common scenario is the so-called "click cycle". You can hear the compressor trying to start: there is a dull hum that lasts 2-5 seconds, followed by a loud click. After this there is silence, lasting from a few seconds to a couple of minutes, after which the cycle repeats. This means that start relay either does not close the contacts or does not open them in time, and the thermal protection forcibly de-energizes the circuit.
In some cases, the refrigerator may work, but not cool properly. If the relay is stuck closed, the starting winding remains energized for too long. This leads to rapid overheating of the engine and tripping of the thermal protection. As a result, the compressor operates jerkily, not having time to reach full power, and the temperature in the chambers rises. The products begin to deteriorate, and there may be no frost on the back wall or, conversely, ice may appear unevenly.
⚠️ Attention: If you smell a persistent smell of burnt plastic or see a melted plastic case in the compressor area, immediately unplug the device. Operation in this condition can lead to a fire in the wiring.
Another important symptom is a complete lack of response to being plugged into the network. The light inside is on, the fan (if there is one in the No Frost system) may make noise, but the compressor is silent. This may indicate that the contacts inside the relay have completely oxidized or burned out, and the electric current is simply not reaching the motor windings. In such a situation, the refrigerator ceases to be a refrigerator and turns into an ordinary cabinet.
Visual and acoustic diagnostics of breakdown
Before disassembling the unit, it is worth conducting an initial diagnosis, relying on hearing and visual inspection. Unplug the refrigerator and move it away from the wall to gain access to the back. Remove the protective cover of the compressor compartment (usually it is held on by latches or bolts). Carefully inspect the area where the wires connect to the compressor. You can often see traces of soot, blackening of the insulation, or even melting of the relay body itself.
If no visual defects are detected, you can conduct an acoustic test. Turn on the refrigerator and listen. Proper startup occurs quickly and with one quiet click. The malfunction is manifested by a series of clicks. You can also carefully (observe safety precautions!) touch the relay body during operation. If it is excessively hot (you cannot hold your finger for more than 2-3 seconds), this is a sign that a short circuit current is passing through it or it is operating in abnormal mode.
- 👀 Inspection of the contacts: The presence of black carbon, oxides or bending of the contact plates inside the relay.
- 👂 Sound pattern: Ringing a metallic click versus a dull hissing or crackling sound.
- 🌡️ Temperature conditions: Excessive heating of the relay housing or the wires suitable to it.
It is important to note that symptoms may vary depending on the type of relay. In models with positor (PTC relay), a breakdown often looks like complete silence of the compressor, since the ceramic element simply loses its conductivity properties. In classic electromagnetic relays, mechanical jamming of the tongue is more common. In any case, if the diagnostics points to this unit, replacing it is the most logical solution.
☑️ Diagnostics of the refrigerator relay
Table of signs: serviceable relay vs faulty
To systematize knowledge and facilitate diagnostics, we offer a summary table comparing the behavior of a serviceable and faulty unit. This data will help you quickly identify the problem and distinguish a relay failure from other faults, such as a freon leak or a thermostat malfunction.
| Monitoring parameter | Good relay | Faulty relay |
|---|---|---|
| Sound when startup | One quiet click turning into a smooth hum | A series of loud clicks, the hum stops after 3-5 seconds |
| Relay case temperature | Warm (40-50°C) | Very hot or, conversely, icy |
| Compressor operating mode | Works in cycles (on/off based on temperature) | Frequent starts, jerky operation or complete failure |
| Contact condition | Clean, without soot and oxides | Blackened, melted, with curvature |
| Reaction to power off | Restart after 3-5 minutes | Attempt to start immediately or no reaction |
Analyzing the data from the table, we can conclude that the combination of sound signals and temperature conditions is the most reliable indicator. However, it is worth remembering that similar symptoms (for example, clicks and stops) can also occur in turn-to-turn short circuit the windings of the compressor itself. Therefore, if replacing the relay did not help, the problem lies deeper.
Why can’t you ignore clicks?
Constant attempts to start with a faulty relay lead to burnout of the compressor windings. Repairing a compressor is often not economically feasible, so replacing a cheap relay is the salvation of the entire refrigerator.
Consequences of operating a refrigerator with a broken relay
Ignoring the problem and continuing to operate a refrigerator with a faulty start or thermal relay is the path to serious financial losses. The biggest danger is that the compressor operates under extreme conditions. With each unsuccessful start, a current 5-7 times higher than the rated current passes through the windings. This leads to overheating of the insulation and, ultimately, to turn-to-turn short circuit.
In addition, if the relay does not open the starting winding circuit in time, the engine does not reach operating mode, but continues to operate on the starting winding, which is not designed for long-term load. This causes rapid wear of the mechanical parts of the compressor (piston group) and can lead to jamming. In this case, the entire unit will need to be replaced, which is up to 80% of the cost of a new refrigerator.
Another risk is fire hazard. Overheating of the relay contacts and associated wires can cause plastic components or insulation to ignite. This is especially true for older models, where the wiring may have already lost its elasticity. Thermal protection a faulty relay may not operate at the right time, allowing the temperature to rise to critical values.
⚠️ Attention: Do not try to “revive” the relay by tapping or briefly closing contacts manually. This can lead to electric shock and will finally kill the compressor.
It is also worth mentioning food spoilage. Unstable operation of the refrigerator leads to temperature fluctuations, which is detrimental to perishable goods. Even if the compressor starts sometimes, it may not have time to gain the required power to maintain the mode, especially in the hot season or when the chambers are fully loaded.
Replacement algorithm and checking the new element
If diagnostics confirm a malfunction, the relay must be replaced. This is one of the few refrigerator repair procedures that you can do yourself if you have basic skills and tools. The main rule is to buy a relay with exactly the same markings as the old one. They are not universal and are selected for a specific power and type of compressor.
The replacement process begins with completely disconnecting the device from the power supply. Then the back cover is removed, the wires are disconnected (it is advisable to photograph their location) and the old relay is removed. It is usually simply slipped onto the compressor contacts and secured with a bracket or latches. The new device is installed in the same orientation (usually the “UP” arrow should face up), after which the wires are connected.
- 🛒 Purchase: Find the markings on the old relay (for example, RKT, PTC, CSR) and select an analogue.
- 🔧 Dismantling: Remove the fixing bracket and carefully pull it off relay from the compressor contacts.
- 🔌 Installation: Push the new relay all the way, make sure it is in tight contact and snap the latch.
After installation, reassemble the structure in the reverse order and turn on the refrigerator. During the first minutes of operation, carefully monitor the startup process. The compressor should start the first time, run smoothly, without vibrations or extraneous sounds. After 10-15 minutes, check the temperature of the new relay case - it should not heat up above 50-60 degrees.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay?
Theoretically, you can start the engine by applying voltage directly to the starting winding, but this is strictly forbidden living conditions. Without a relay, the compressor will not be able to operate normally, it will quickly overheat and burn out. In addition, this creates a direct threat of fire and electric shock.
How much does it cost to replace a relay and is it worth calling a technician?
The cost of the relay itself usually ranges from 300 to 1500 rubles, depending on the model. The work of a master can cost from 1,500 rubles. Given the ease of replacement, it is often more cost-effective to do it yourself if you are confident in the diagnosis. However, if you are not confident in your abilities, calling a specialist will protect you from mistakes.
Why did the new relay burn out after a week?
If the new relay failed quickly, then it is not the reason. Most likely, the compressor itself is faulty (interturn short circuit, jamming) or there are problems with the voltage in the network. In this case, the relay acts as a “victim”, taking the blow. An in-depth diagnosis of the motor is required.
What is the difference between a starting and thermal relay?
The starting relay is responsible for briefly supplying current to the starting winding to start the engine. The thermal relay (protection) monitors the current strength and temperature, opening the circuit in case of overload. They are often combined in one housing, but perform different functions.
Is it possible to repair an old relay?
In most cases, repairing a relay is impossible or impractical. If the contacts are burnt or the posistor has lost its properties, it is impossible to restore their factory characteristics. Simply stripping the contacts will only give a temporary effect, after which the breakdown will occur again. Only replacement is recommended.