Refrigerator thermal relay: why it is needed and how it works

Many owners of household appliances are faced with a situation where a refrigerator stops freezing or starts making strange clicking sounds. Often the source of the problem is not the compressor itself, but its “bodyguard” - the thermal relay. This small component plays a critical role in the cooling system, protecting the expensive motor from overheating and current overload. Understanding what What is a refrigerator thermal relay for? it is used and how it functions will help you quickly diagnose a breakdown and avoid replacing the entire unit.

If you hear the motor trying to start, making a hum, and then there is a click and silence, this is a sure sign protection activation. In some cases, the device has simply failed and requires replacement; in others, it has honestly done its job, saving the engine from combustion. It is necessary for anyone who wants to extend the life of their equipment and save on repairs to understand the nuances of the operation of this element.

In this article we will analyze in detail the design of the protective mechanism, the reasons for its operation and testing methods. You will learn how different types of relays differ, what parameters to pay attention to when purchasing a new part, and whether it is possible to temporarily run the system bypassing the protection (although this is highly undesirable). Knowledge of these aspects turns complex diagnostics into an understandable algorithm of actions.

Main function and principle of operation

The main task of this element is to automatically open the electrical circuit when the permissible current or temperature is exceeded. Thermal relay works in tandem with a starting element, ensuring safe start and operation of the compressor. Inside the case there is a bimetallic plate that reacts to heat. When the current passing through the motor windings becomes too high, the plate bends and opens the contacts, stopping the supply of power.

The principle of operation is based on the physical property of different metals to expand at different rates when heated. It is this feature that allows the device to respond not only to the current strength, but also to the temperature of the compressor housing. If the motor operates under extreme conditions, the protection will work faster, preventing the winding insulation from melting. This is especially important for older models, where wear of rubbing parts can lead to increased load.

After cooling, the bimetallic plate returns to its original position and the circuit is closed again. This cycle can be repeated several times until the cause of the overload is eliminated or until the part finally fails. It is important to understand that frequent operation of the protection is always a signal of a deeper problem in the cooling or power supply system.

Types of protective devices for refrigerators

Modern and classic household appliances use various modifications of protective mechanisms. Most often, there are combined devices combined into one housing with a starting element, but there are also separate options. The type of device directly depends on the model of the compressor and the year of manufacture of the refrigerator. For example, electronic protection modules can be used for inverter systems, while classic units are equipped with mechanical RTK or RTP.

Mechanical relays are divided into two main types according to the connection method and operating principle:

• 🔹 Posistor (starting): use a ceramic element that changes resistance when heated, often working in conjunction with a separate thermal release.
• 🔹 Induction: react directly to the strength of the current flowing through the coil and require precise tuning for a specific motor.

Devices with an external heating coil deserve special attention. In them, the bimetallic plate is heated not only by the passing current, but also by a special winding. This provides a more accurate and faster response to overload. When choosing a spare part for repair, it is extremely important to take into account not only the dimensions, but also the standard size specified in the technical documentation. Installing an element that is not suitable for its characteristics can lead to false alarms or, conversely, to a lack of protection.

Signs of a malfunctioning thermal relay

Fault diagnosis often begins with an analysis of the behavior of the refrigerator. If you notice that the equipment is working intermittently, you should pay attention to the characteristic symptoms. Faulty thermal relay often manifests itself long before the system completely fails. Ignoring the first signs can lead to expensive compressor repairs, so be attentive to the signals of your equipment.

The main symptoms indicating problems with the protective mechanism:

• 🔸 The refrigerator hums for 5-10 seconds, then a click is heard, and the motor goes silent.
• 🔸 The compressor gets very hot (up to 80-90 degrees), although it works for a short time.
• 🔸 There is no characteristic click when trying to start, or the clicks come in a series without stopping the engine.
• 🔸 The circuit breakers in the electrical panel are knocked out when turning on the refrigerator in the network.

It is important to distinguish relay failure from other malfunctions. For example, if the engine hums but does not start, the problem may be a stuck piston or lack of coolant. In such cases, even a working relay will constantly trip, trying to protect the engine. Therefore, visual inspection and testing of contacts with a multimeter are mandatory diagnostic steps. If the contacts are burnt or oxidized, their resistance increases, which causes additional heating and false alarms.

⚠️ Attention: If during disassembly you find blackened plastic or melted wires in the contact area, under no circumstances install a new part without checking the motor windings. A short circuit inside the compressor will instantly damage the new relay.

Instructions for testing and diagnostics

To carry out high-quality diagnostics, you will need a minimum set of tools: a screwdriver, pliers and a multimeter. Before starting work, be sure to disconnect the refrigerator from the power supply. Safety is the number one priority when working with electrical components. Remove the rear cover at the bottom of the unit to gain access to the compressor.

The test process is as follows:

First, a visual inspection is performed. Shake the part: if a ringing or knocking sound is heard inside, it means the mechanism is damaged and requires replacement. Next comes checking the integrity of the contacts using a tester. Switch the multimeter to continuity or resistance measurement mode. The probes are applied to the contact terminals. On a working device, the resistance should be close to zero (for normally closed contacts in a cold state). If the device shows one or infinity, the circuit is broken.

Pay special attention to the condition of the bimetallic plate. It should not show signs of severe overheating, deformation or corrosion. Sometimes the cause of failure is not the part itself, but the oxidation of the contacts on the connector. Stripping the contacts can temporarily solve the problem, but it is better to make a complete replacement, since the reliability of the connection has already been compromised. After checking all the elements, assemble the circuit in the reverse order and perform a test run.

Is it possible to test the relay without a multimeter?

Theoretically, you can apply 220V voltage through the fuse, but this is dangerous and does not provide accurate information about the operation current. It is better to use a tester or replace the part with a known good one.

Compatibility and characteristics table

When selecting an analogue, it is important to take into account not only the manufacturer, but also the electrical parameters. Different compressor models require different cut-off currents. Below is a table with common types of relays and their characteristics, which will help you navigate the range of spare parts.

Please note that labeling may vary depending on the manufacturer. For example, Danfoss uses its own encoding system, which does not always coincide with Soviet standards. When purchasing, be sure to compare the appearance and location of the contacts. Even if the electrical parameters are the same, the unsuitable shape of the housing may not allow the part to be secured to the compressor.

Replacing a thermal relay with your own hands

If diagnostics have confirmed a malfunction, proceed to replacement. This process does not require high qualifications, but it does require accuracy. The main rule is to observe the polarity of the connection, although in most mechanical relays it is not critical; you cannot mix up the contacts of the starting and working windings. Usually the wires are color coded or labeled on the diagram.

Carefully remove the old relay, remembering which wire is connected where. It's best to take a photo before taking it off. Install the new part, fitting it tightly onto the compressor rod. Make sure it is locked in a vertical position, like the previous one - this is important for the correct operation of the gravity mechanism (if there is one). After connecting the wires, check the reliability of the connections by lightly pulling them.

After assembly, turn on the refrigerator. In the first seconds, a characteristic startup click may be heard. If the motor runs smoothly and after some time cold appears in the chamber, the repair can be considered successful. If the clicks are repeated, perhaps the problem is deeper - in the compressor itself or the heat removal system.

⚠️ Attention: Technical characteristics of compressors may vary slightly in different modifications of the same model. Always check the markings on the nameplate of your unit with the data on the new relay before installation.

Frequently asked questions (FAQ)

Is it possible to operate a refrigerator without a thermal relay?

Strongly not recommended. Operation without protection will lead to overheating and burning of the compressor windings at the first overload. This will turn a minor repair into a replacement of an expensive motor or the entire refrigerator.

Why does a new relay burn out immediately after installation?

Most likely, the reason is not the relay, but a compressor malfunction (interturn short circuit) or problems with the voltage in the network. It is also possible that a relay with the wrong cut-off current was selected.

How often do you need to change a thermal relay?

A working relay does not have a scheduled replacement period. It lasts as long as the compressor, unless emergency situations occur. Replacement is made only if a malfunction is detected.

Does the temperature in the room affect the operation of the relay?

Yes, in a hot room the compressor works with more load and heats up more. This can lead to more frequent thermal protection activations, which is a normal reaction of the system.