The situation when the refrigerator compressor works without interruption, without entering the normal rest cycle, always causes concern for the owner of household appliances. The constant hum of the engine not only irritates the ear, but also indicates a serious malfunction in the thermoregulation system or start-up protection system. Most often, the user notices a problem when the food begins to freeze, and a thick coat of ice forms on the back wall of the chamber.
The main element responsible for turning the engine on and off is the start relay, but it only executes commands coming from the thermostat. If this control unit does not open the circuit, the compressor continues to pump freon until the thermal protection trips or the windings overheat. Understanding the physics of the process will help you avoid costly repairs if you notice the first signs of a malfunction in time.
In this article we will look in detail at why refrigerator relay it may not turn off, what factors affect the operation of the contacts and how to independently determine the source of the problem. You will learn about the difference between a sticking trigger mechanism and a broken temperature sensor, and also receive a step-by-step algorithm for checking the electrical circuit.
The principle of operation of the starting relay and thermostat
To understand the reasons for the continuous operation of the motor, it is necessary to clearly understand the interaction of the main components of the refrigerator unit. Start relay is an electromagnetic or posistor device that supplies a pulse to start the engine when voltage is applied. As soon as the motor picks up speed, the relay should turn off the starting winding, leaving only the main winding working. If this mechanism jams, the engine may hum, but not start, or operate in emergency mode.
However, it is not the start relay that is responsible for the work-rest cycle, but the thermostat (thermostat). It is he who measures the temperature inside the chamber and physically opens the contacts that supply power to the entire compressor circuit when a predetermined minimum is reached. If the thermostat is “stuck” in the “on” position or its capillary tube has lost sensitivity, the shutdown signal simply does not arrive.
⚠️ Attention: Continuous operation of the compressor for more than 24 hours without breaks can lead to thermal breakdown of the winding insulation and complete failure of the unit. If such a malfunction is detected, it is recommended to temporarily disconnect the device from the network until diagnostics are carried out.
It is important to distinguish between concepts: the starting relay is responsible for starting the motor, and the thermostat is responsible for stopping it. When they say that “the relay does not turn off,” they often mean either sticking of the contacts of the thermostat itself, or a malfunction of the starting device, which prevents the motor from correctly switching to operating mode, which is why the protection is activated, but the cycle does not complete.
What is the difference between an electromagnetic and a posistor relay?
Electromagnetic relays (of the old sample) have a movable core and coil, they emit a characteristic click when operating. PTC relays (modern ones) have no moving parts; inside them there is a ceramic element that heats up and changes the resistance, opening the circuit. They operate silently and are considered more reliable, but if they break down they often require replacement along with the protective thermal relay.
Main causes of sticking relay contacts
One of the most common mechanical problems is physical welding or sticking of the contacts inside the relay housing. When the circuit opens, an electric arc occurs between the contacts, which eventually melts the metal. As a result, the contacts stick to each other, and the circuit remains closed even after the control signal has disappeared.
Another reason could be a violation of the housing geometry or moisture getting inside the electrical unit. If relay contacts are oxidized, the resistance at the connection point increases, causing local overheating, which only aggravates the process of metal deformation. In older models of refrigerators, such as Biryusa or Atlant, often occurs due to natural wear and tear of the mechanism.
It is also worth considering the state of the electrical network itself. Voltage surges can cause the relay's electromagnetic coil to operate incorrectly, leaving the armature in a pulled position. In such cases, the relay stops performing its switching function and requires immediate replacement.
Thermostat malfunctions as the main reason
In the vast majority of cases, when the compressor does not turn off, the thermostat is the culprit. This device is a simple mechanical switch that is sensitive to changes in gas pressure or liquid volume in a capillary tube. If the tube has lost its tightness and the freon has evaporated from it, the bellows compresses and cannot break the contact chain.
Diagnostics of the thermostat often requires dismantling the unit. It is necessary to remove the terminals and connect them directly, bypassing the sensor. If after this the refrigerator starts working and begins the cooling cycle, then the problem lies in the sensor. However, you cannot leave the device in this state - it will freeze indefinitely until you manually break the circuit.
In modern models with electronic control, the role of a thermostat is performed by thermal sensor, transmitting signals to the control module. If the sensor “lies” and shows that the chamber is warm, the control board will keep the compressor on. Testing such systems requires a multimeter and knowledge of resistances at different temperatures.
⚠️ Attention: When replacing a thermostat, it is critical to use a model with similar parameters. Installing the wrong sensor may result in the refrigerator either not turning on at all or never turning off.
The influence of freon leakage on the operation of the automation
Paradoxically, a refrigerant leak often leads to continuous operation of the compressor. The logic here is simple: due to a lack of freon, the temperature in the chamber does not drop to the set value. The thermostat “sees” that there is not enough cold and does not give a command to turn off, forcing the motor to work hard in an attempt to compensate for the loss of refrigerant.
In such situations, the relay is formally in good order - it is ready to turn off the motor, but the command to do so is simply not received. A leak can be determined by indirect signs: poor cooling, hot sides of the refrigerator (in areas of the heating circuit) or the appearance of oily spots under the unit.
If you are faced with such a situation, further operation of the refrigerator is pointless and dangerous for the compressor. It is necessary to call a technician to find the location of the leak, evacuate the system and refill with new freon.
Diagnostics and checking the electrical circuit
To accurately determine the malfunction, it is necessary to conduct a visual and instrumental inspection. The first step is to turn off the power to the refrigerator and remove the back cover near the compressor. Pay attention to the starting relay: if it is blackened, has traces of burning or melted plastic, its replacement is required.
Checking the integrity of the thermostat contacts is carried out using a multimeter in continuity mode. At room temperature, the contacts should be closed (if the thermostat is mechanical and set to minimum). When the sensor is cooled (for example, by putting it in the freezer for 15 minutes), the circuit should open, which will confirm the serviceability of the device.
Below is a table that helps classify symptoms and probable causes:
| Symptom | Probable cause | Required action |
|---|---|---|
| The compressor hums, but does not start | The starting relay is faulty | Replacing the relay |
| The motor runs without stopping, there is cold | Sticking thermostat contacts | Replacing the thermostat |
| The engine runs without stopping, there is no cold | Freon leakage | Searching for leaks and refilling |
| A crackling sound is heard, the motor turns off after 10 seconds | The winding is burned out or the piston is jammed | Repairing or replacing the compressor |
The procedure for replacing the starting relay
If diagnostics have confirmed that the problem is in the starting device, you can replace it yourself, having minimal skills in working with tool. The process does not require special knowledge, but requires caution and compliance with safety precautions.
☑️ Algorithm for replacing the relay
First remove the retaining bracket that holds the relay to the compressor terminals. Carefully remove the device, being careful not to damage the wires. Pay attention to the markings: new relays are often universal and suitable for different models, but it is important that they match the capacity of your compressor.
Install the new relay into place, making sure that it is firmly seated on the contacts. Put on the heat protector (if it is separate) and secure everything with a staple. Plug in the refrigerator and listen: the startup should be confident, without a long hum.
⚠️ Attention: Never try to start the compressor directly, bypassing the thermal protection. This can lead to a fire if the motor is jammed, since the protection will not turn off the power when overloaded.
When you need to call a professional technician
Despite the apparent simplicity, some malfunctions require the intervention of a specialist with a license and special tools. If after replacing the relay and thermostat the situation has not changed, the problem may lie in the compressor itself or the refrigerant circulation system.
In addition, if you notice that the refrigerator tubes are swollen, there are traces of oil or the smell of burnt wiring, further independent diagnostics are prohibited. In such cases, the risk of getting an electric shock or causing a fire is too great.
A professional technician will be able to carry out a full diagnosis using a pressure manifold, check the pressure in the system and the tightness of the circuit. This will allow you to accurately determine why refrigerator relay does not turn off, and eliminate the root cause, and not just the symptoms.
Is it possible to operate a refrigerator if it does not turn off?
Short-term operation (up to 1-2 hours) on a hot day or after loading a large amount of food is acceptable. However, long-term operation without breaks (more than 20 hours) will lead to compressor overheating, oil degradation and eventual engine failure. Saving on repairs now will lead to the purchase of a new refrigerator later.
Why does the refrigerator not turn off for a long time after defrosting?
After defrosting, the inner walls and food are warm. The compressor requires significantly more time (up to 6-8 hours in the first cycle) to cool the chamber volume to the set temperature. If after this it continues to work without stopping, this is a sign of a malfunction.
Does the position of the refrigerator affect the operation of the relay?
Yes, if the refrigerator is standing with a strong slope, oil from the compressor can flow into the circulation circuit, creating a hydraulic lock. This complicates the operation of the piston group and can cause incorrect operation of the thermal protection or start relay.