Refrigerator thermal relay: device, principle of operation and fault diagnosis

The thermostat (or thermostat) is a key element of the refrigerator control system, which is responsible for maintaining the set temperature. Without it, the compressor would either run continuously, overheating and consume huge amounts of electricity, or not turn on at all, allowing food to spoil. Understanding the operating principle of this device will help not only to operate the equipment correctly, but also to recognize signs of its malfunction in time.

In modern refrigerators, the thermal relay can be mechanical or electronic. The former are still widely used due to their simplicity and reliability, the latter are found in models with digital control. Despite the differences in design, their main task remains the same: control the temperature in the chamber and to provide signals to turn the compressor on/off. If the relay fails, the refrigerator either stops freezing, or, conversely, freezes food in the “zero” zone.

In this article we will look in detail at how the thermal relay works, on what principle it works in different types of refrigerators (No Frost, drip, two-chamber), and we will also learn how to diagnose its breakdowns without calling a technician. We will pay special attention mechanical thermostats with a bellows tube - they are most often installed in budget models, and they require a specific approach when checking.

Thermal relay device: what it consists of and what it looks like

Thermal relay is a compact device, usually located inside the refrigeration chamber (less often - in freezer or behind the rear panel). Externally, it is a plastic case with an adjustment wheel (in mechanical models) and contacts for connecting wires. The main components of the thermostat:

• 🔹 Bellows tube —a thin copper or brass tube filled with freon or refrigerant. It reacts to changes in temperature by expanding or contracting.
• 🔹 Contact group —a mechanical switch that closes/opens the compressor power circuit.
• 🔹 Spring mechanism —provides a specified force for operation contacts.
• 🔹 Adjusting screw —allows you to change the response threshold (in service models).
• 🔹 Case with fastenings —protects internal parts from moisture and mechanical damage.

In electronic thermostats, instead of a bellows tube, a thermistor (temperature sensor) is used, and the role of the “brain” is played by a microcircuit. Such devices are more accurate and durable, but their repair requires special equipment. Mechanical relays can be checked and replaced independently, having a minimum set of tools.

The bellows tube is the most vulnerable element of a mechanical thermal relay. Over time, it may lose its seal, which will lead to gas leakage and incorrect operation. There are also frequent cases when the tube moves away from the body due to vibrations or careless repairs. In this case, the relay will operate with a delay or not respond to the temperature at all.

The principle of operation of a thermostat in a refrigerator

The operation of a thermostat is based on the physical properties of gases and liquids: when heated, they expand, when cooled, they contract. In mechanical thermostats, this process occurs inside bellows tube, which is connected to the contact group. The operating algorithm looks like this:

1. The temperature in the chamber increases (for example, after opening the door or loading warm products).
2. Gas in the bellows tube heats and expands, pressing on the membrane.
3. The membrane moves the lever, which closes the contacts - the compressor turns on.
4. After the chamber has cooled gas is compressed, the pressure drops, the contacts open - the compressor turns off.

The cycle is repeated automatically, maintaining the temperature within the specified limits. Electronic thermostats use a signal from a thermistor instead of mechanical pressure, which is processed by a microcontroller. It compares the current temperature with the one set by the user and controls the compressor relay.

An important nuance: the thermal relay not only turns the compressor on/off, but also controls the duration of its operation. For example, if the refrigerator door is left open for a long time, the relay will force the compressor to run continuously until the temperature returns to normal. In some models (Samsung RB30J3000WW, Indesit DF 4180 W), the thermostat also controls the system fan No Frost.

It is interesting that in two-chamber refrigerators (Atlant MXM 2808-90, LG GA-B489 YGZ) they often install two thermal relays: one for the refrigerator compartment, the other for the freezer. This allows you to independently regulate the temperature in each compartment. In models with one compressor, the relays operate alternately, priority is usually given to the freezer compartment.

Signs of a faulty thermal relay: when it’s time to sound the alarm

A faulty thermal relay manifests itself quite clearly. The main symptom is temperature violation, but there are other “bells” that are worth paying attention to. Here are typical signs of a breakdown:

• ❄️ The compressor works without stopping —the relay is “stuck” in the closed state.
• 🔥 The refrigerator does not cool —the contacts do not close, the compressor does not turn on.
• ❓ Spontaneous shutdown —the relay opens the circuit ahead of time.
• ⚡ Clicks without starting compressor —the mechanism is activated, but the contacts do not hold the load.
• 🌡️ Temperature mismatch with settings (for example, in a freezer +5°C when set to −18°C).

One of the most insidious defects is unstable operation. The relay may either work normally or malfunction, which makes diagnostics difficult. For example, a refrigerator Beko CN 335120 X can freeze properly for a week, and then suddenly “go into hibernation” for several hours. Most often this is due to loss of tightness of the bellows tube or oxidation of contacts.

Another alarm signal - ice on the back wall in refrigerators with a drip system (Whirlpool ARC 4201, Bosch KGN39XL30R). This indicates that the compressor is running too long and the thermostat is not turning it off in time. In models with No Frost a similar symptom - constant operation of the fan even with the door closed.

⚠️ Attention: If the refrigerator has stopped cooling, do not rush Blame the thermostat. First check if it worked thermal protection of the compressor (it turns off the power if it overheats). To do this, just unplug the plug from the socket for 10–15 minutes and turn it on again. If the compressor works, the problem is not in the thermostat.

How to check the refrigerator thermostat yourself

Diagnostics of the thermostat does not require complex equipment - just a multimeter (or even an indicator light) screwdrivers) and basic knowledge of electrical engineering. The main rule: carry out all work with the power off. The testing algorithm depends on the type of relay.

Checking a mechanical thermal relay

To test a mechanical thermostat:

1. Disconnect the refrigerator from the mains and remove the protective casing (usually it is secured with latches or screws).
2. Find the thermal relay - it is connected to the compressor two or three wires (phase, neutral and sometimes ground).
3. Carefully remove the wires from the terminals, first photographing or recording their location.
4. Switch the multimeter to mode diagnosis and connect the probes to the contacts 3 and 4 (usually they are marked).

At room temperature, the contacts should be opened (the device will emit a beep). If this does not happen, the relay is faulty. For additional checking, you can:

• 🧊 Place the thermostat in cold water with ice for 2-3 minutes - the contacts should open.
• 🔥 Heat the relay with a hairdryer (be careful, do not overheat!) - the contacts should close.

If there is no reaction - replacement is required. Also inspect bellows tube for damage: cracks, kinks or gas leaks (it must be sealed and straight).

Disconnect the refrigerator from the network|Take a photo of the wire connection|Check the contacts with a multimeter|Test the reaction to cold/heat|Inspect the bellows tube-->

Checking the electronic thermostat

Electronic thermostats are checked differently. Here you need:

1. Check power supply on the control board (should be 5V or 12V, depending on the model).
2. Measure the resistance thermistor (temperature sensor) at different conditions:
   • 🌡️ At room temperature: ~10–50 kOhm.
   • ❄️ In cold (0°C): ~100 kOhm.
   • 🔥 When heating (50°C): ~1–5 kOhm.

Ring the circuits between the thermistor and the board for an open.

If the resistance of the thermistor does not change or is equal to zero/infinity, the sensor is faulty. In some models (Samsung RL-34 EBSA, Liebherr CP 3023), the electronic relay can be “reset” by turning off the power for 10–15 minutes. If this does not help, you will need to replace the module.

⚠️ Attention: In electronically controlled refrigerators (LG InstaView, Samsung Family Hub), the thermal relay is often integrated into the main board. Self-repair of such systems risks failure of the entire unit. If you are not confident in your skills, it is better to contact the service.

Typical thermal relay failures and their causes

Most thermal relay malfunctions are associated with natural wear and tear or external factors. Let's look at the most common problems and their causes:

One of the most unpleasant breakdowns - sticking of contacts in a closed state. In this case, the compressor works without stopping, which leads to:

• 🔌 Increased energy consumption (light bill can increase 2-3 times).
• ⚡ Overheating of the compressor windings and its premature exit from building.
• ❄️ Freezing of the evaporator and disruption of refrigerant circulation.

If you notice that the refrigerator Indesit BIAA 13 or Atlant XM 4021-000 began to “buzz” incessantly, first check the thermal relay. Sometimes the problem is solved by simply cleaning the contacts with alcohol or an eraser, but more often replacement is required.

What to do if the thermal relay “clicks”, but the compressor does not starts?

This symptom indicates that the relay contacts are working properly, but the compressor does not receive enough voltage. The reasons may be the following:

1. Oxidation of the terminals on the compressor or start-up relay.

2. Malfunction of the starting capacitor (checked with a multimeter in capacitance measurement mode).

3. Interturn short circuit in the compressor windings (diagnosed by measuring the resistance of the windings).

4. Power problems (check the voltage in the outlet - it should be 220V ±10%).

If you are not sure of the diagnosis, it is better to call a specialist - attempts to "reanimate" the compressor using homemade methods often lead to its final breakdown.

How to replace a thermal relay with your own hands

Replacing a thermal relay is one of the few operations that can be performed independently, without special education. The main thing is select an analogue, compatible with your refrigerator model. Main selection criteria:

• 🔧 Relay type (mechanical/electronic).
• 📏 Bellows length tubes (must correspond to the original).
• 🔌 Connection diagram (number and location of terminals).
• 🌡️ Temperature adjustment range (for example, from −30°C to +10°C).

Popular thermal relay models and their analogues:

• Danfoss 077B6 → K59-L1411, Ranco K59.
• Orion TR-10 → TAM-133-1M, Ranco K56.
• Sensormatic TS-04 → TAM-112, Danfoss 077D6.

To replace you will need:

• Screwdriver (cross/flat).
• Pliers.
• Multimeter (to check the new relay before installation).
• Heat shrink tubing or electrical tape.

Step-by-step instructions:

1. Unplug the refrigerator and defrost (if there is ice on the evaporator).
2. Remove the protective cover to access the relay.
3. Take a photo or write it down wire connection diagram.
4. Disconnect the wires and carefully remove the old relaywithout damaging the bellows tube.
5. Install a new relay, connect the wires according diagram.
6. Fix the bellows tube in the same position (it should fit tightly to the evaporator).
7. Check the operation of the refrigerator within 1-2 hours.

⚠️ Attention: In refrigerators with a system No Frost (Samsung RL-38 EBSW, LG GA-B429 SLGL) the thermostat is often connected to a timer defrost. When replacing the relay, you may need resetting the timer (usually there is a special button or jumper on the board for this).

Fault prevention: how to extend the life of the thermal relay

The service life of the thermal relay directly depends on the operating conditions of the refrigerator. By following simple rules, you can avoid most breakdowns:

• 🧊 Regularly defrost the refrigerator (even if it has No Frost). Ice on the evaporator increases the load on the thermostat.
• 🚪 Do not keep the door open for a long time - this leads to sudden temperature changes.
• 🔌 Use a voltage stabilizerif your network has frequent horse racing.
• 🧹 Clean the condenser and fan from dust (especially in models No Frost).
• 🌡️ Do not set the maximum cooling mode unnecessarily.

Pay special attention bellows tube to the mechanical relay. It should not:

• 🔹 Touch the walls of the refrigerator (it may rub).
• 🔹 Be bent or twisted (this interferes with gas circulation).
• 🔹 Covered with ice or condensation (leads to corrosion).

If your refrigerator Stinol RF-305 or Pozytron KR-105 has served for more than 10 years, it makes sense preventatively replace the thermal relay, even if it still works. The cost of a new relay (300–1000 rubles) is not comparable with the risk of compressor failure due to a faulty thermostat.

FAQ: Frequently asked questions about the refrigerator thermal relay

Is it possible to repair the thermal relay or just replace it?

Mechanical thermal relays with oxidized ones contacts or misaligned adjustment can be repaired (clean, bend the contacts, calibrate). However, if the thermistor circuit is broken, repair is impossible - only replacement. gas leakage from the bellows tube or the thermistor circuit is broken, repair is impossible - only replacement.

How to determine what is broken: a thermal relay or compressor?

If the compressor does not turn on at all, check the thermal relay (ring the contacts). If the relay is working properly, but the compressor does not start, check:

• Start protection relay (should click when turned on).
• Starting capacitor (checked) multimeter).
• Compressor windings (the resistance between the terminals should be 20–50 Ohms).

If the compressor hums but does not start, the problem is interturn short circuit or jammed piston.

What to do if the new thermal relay does not work correctly?

Possible reasons:

• Incorrect installation bellows tube (it should fit tightly to evaporator).
• Model mismatch (for example, a relay from Atlant is not suitable for Indesit).
• Damage to the wiring during connection.

Check all connections and compare the characteristics of the new one and the old relay.

Why does the thermostat click, but the refrigerator does not cool?

This is a sign that the relay sends a signal to the compressor, but:

• Compressor does not receive power due to an open circuit.
• Start-protective relay does not work (does not close the starting winding).
• In the system no refrigerant (freon leak).

Comprehensive diagnostics are needed.

Is it possible to temporarily operate a refrigerator without a thermostat?

Technically yes, but this it is fraught with breakdown of the compressor.. Without a thermal relay, the compressor will either work constantly (overheating) or not turn on at all. temporary measure you can connect the compressor via a timer, simulating work/rest cycles, but not longer than 1-2 days.