Why the thermal relay on the refrigerator is triggered: causes and repairs

Sudden Stopping the operation of a refrigeration unit often takes you by surprise, especially when the ice inside is already starting to melt and the food is losing its freshness. One of the first symptoms of a serious malfunction is a characteristic click, followed by silence or attempts by the engine to start, which are immediately interrupted. This is exactly how thermal relaybehaves, performing the function of guarding the safety of your equipment. It breaks the electrical circuit to prevent catastrophic overheating and failure of an expensive compressor.

Understanding the nature of this process is critically important for the owner of the equipment, since ignoring protection signals can lead to complete combustion of the motor. Protective device reacts to an increase in the temperature of the windings or consumed current exceeding permissible limits. If the refrigerator has stopped cooling and the relay is constantly clicking, you must immediately stop trying to turn it on and carry out diagnostics.

In this article we will analyze in detail the mechanics of the protection, the main reasons for its activation and algorithms for action when a malfunction is detected. You will learn in which cases you can deal with the problem yourself, and when calling a specialist becomes the only solution. Correct interpretation of the symptoms will save you significant money on repairs.

The principle of operation of the protective mechanism

The thermal relay is a compact electromechanical device installed directly on the compressor housing or in close proximity to it. Inside the case there is a bimetallic plate, which has the unique property of bending under high temperature. When more than rated current passes through the motor windings, or when the housing temperature reaches a critical point, the plate deforms and opens the contacts. This action instantly de-energizes electric motor, stopping its operation.

After cooling, the bimetallic element returns to its original position, closing the circuit again. It is this process that we hear as periodic clicks if the cause of overheating is not eliminated. The design may vary depending on the manufacturer: some models use a tablet with a thermoactive substance, others use a classic plate. It is important to understand that protective starting relay often combines two functions: starting the motor and protecting it from overloads.

⚠️ Attention: Frequent on and off cycles (clocking) due to protection activation lead to rapid wear of the starting winding compressor. Do not try to artificially cool the relay with water or a fan to continue operation - this may lead to a fire.

There are two main types of actuation: current and temperature. Current protection reacts to the current strength in the circuit, which is important when the rotor is jammed or an interturn short circuit. Thermal protection reacts directly to the heating of the case, which is typical for problems with the cooling system or ventilation. In modern units, these functions are often combined for maximum reliability.

Overload and problems with the electrical network

One ​​of the most common reasons why protection is knocked out is unstable voltage in the household network. If the voltage drops below the acceptable threshold (usually 180-190 volts), the motor begins to draw more current to maintain power, which causes it to overheat. Conversely, sudden voltage surges can pierce the insulation or damage the starting winding. To diagnose this factor, it is recommended to use a multimeter or install a voltage stabilizer.

You should also pay attention to the condition of the wiring and socket. Poor contact at the plug connection causes heat, which can be misinterpreted by the protection system or cause the connector to melt. Oxidized contacts inside the relay itself increase resistance, which also contributes to heating. Checking the integrity of the cable and the quality of the connection is the first step in troubleshooting.

Below is a table illustrating the dependence of the relay state on the network parameters:

Faults in the thermal relay itself

Sometimes the problem lies not in the motor, but in the protective device itself. Over time, the contacts inside the relay can burn, oxidize, or stick. This results in the device tripping under normal currents or, worse, not tripping when overloaded. Mechanical damage to the housing or internal bimetallic strip is also a common cause of nuisance shutdowns. A visual inspection may reveal traces of carbon deposits or plastic melting.

Checking the functionality of the relay is carried out using a multimeter in dial mode. When cold, the contacts should ring (show zero or resistance close to it). If the device shows an open or high resistance, the part requires replacement. It is important to select an analogue with identical characteristics indicated on the label, since different compressor models require different protection parameters.

It is worth noting that the starting relay, which is often paired with a thermal one, also affects the overall picture. If the starting winding does not receive an impulse to start, the motor hums but does not spin, which instantly causes thermal shock and triggers the protection. Replacing one component without checking the other may not produce results.

Problems with the compressor and refrigerant

The most serious reason for the protection to trip is internal malfunctions of the compressor itself. An interturn short circuit in the windings leads to a sharp increase in current consumption. The engine tries to run, but due to a short circuit in the turns, it overheats in a matter of seconds. In this case, the relay performs its function, saving the unit from final destruction, but further operation is no longer possible without replacing the motor.

Another common reason is a freon leak or a blockage in the circulation system. When there is little refrigerant, the compressor idles, trying to build up pressure, but cannot be effectively cooled by the returning gas. Failure to cool the engine with refrigerant leads to rapid overheating. The piston group may also jam due to oil production or moisture entering the system, which causes instant blocking of the rotor.

• 🔥 Scuffing in the cylinder - mechanical damage requiring compressor replacement.
• 💧 Moisture in the system - causes water hammer and jamming, complete refilling.
• 📉 Loss of performance - wear of the valves, the motor runs without stopping until the protection works.

Violation of the operating conditions of the refrigerator

Often users create it themselves conditions under which the thermal relay is forced to operate constantly. Installing the refrigerator close to the wall or in a niche without gaps disrupts natural air circulation. The condenser (grid at the back) does not have time to give off heat, the temperature in the engine compartment rises, and the protection turns off the unit. The minimum distance from the back wall to the wall should be 5-7 cm.

Loading the refrigerator with warm food is also stressful for the system. The compressor is forced to work at maximum capacity for a long time in order to cool a large volume of heat. If this is combined with a loose door seal or frequent opening, the motor simply does not have time to cool down between cycles. In the summer, when the ambient temperature is high, the risk of overheating increases many times over.

You should also take into account that some refrigerator models are sensitive to direct sunlight. Heating the housing from the outside increases the overall temperature inside the cabinet, forcing the automation to work in enhanced mode. Relocating equipment to a cooler place often solves the problem of constant shutdowns.

Algorithm for diagnosing and replacing relays

If you decide to carry out repairs yourself, start by completely disconnecting the device from the power supply. Remove the back cover at the bottom of the refrigerator where the compressor is located. Visually assess the condition of the wires and the relay itself: there should be no traces of burning, melting or corrosion. Carefully remove the relay from the compressor contacts, having previously photographed the connection diagram.

To check, shake the relay near your ear: if you hear a ringing, it means the internal mechanical part is damaged or has fallen apart. Test the contacts with a multimeter. If the relay is OK but the problem persists, the compressor itself may be faulty. In this case, professional diagnostics with measurement of winding resistance are required.

⚠️ Attention: Before installing a new relay, make sure that the compressor contacts are clean and not oxidized. If necessary, sand them with fine sandpaper. A loose relay seat will lead to sparking and re-burnout.

The replacement process is simple: the new device is put on the contacts in the same position as the old one, and is fixed with a bracket or frame. After assembly, turn on the refrigerator and check the first cycle of operation. If the motor starts smoothly and runs smoothly without overheating, the repair can be considered successful.

Frequently asked questions (FAQ)