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

The thermal relay is one of the most important, but often underestimated elements of a refrigerator. This small part is responsible for protecting the compressor from overheating, overloads and short circuits. Without a working relay, the motor can fail in a matter of minutes, and repairs will cost half the cost of a new refrigerator. Why do many users find out about its existence only when the unit stops freezing?

In this article we will understand how a thermal relay works, on what principle it operates and what signals it gives about a malfunction. You will learn how to check its performance with a multimeter, which relay models are compatible with popular refrigerators (Atlant, Indesit, Samsung, LG), and when you can do without calling a technician. We will also reveal the myth about “eternal” relays and explain why even original parts sometimes fail after 3-5 years of operation.

What is a thermal relay and why is it needed in a refrigerator

Thermal relay (aka start-protective relay or current relay) is an electromechanical device that performs two key functions:

• 🔌 Starting the compressor —supplies a short-term current pulse to the motor winding to overcome the inertia of the rotor.
• 🔥 Overheat protection — turns off the power if the current exceeds the permissible values (for example, when the shaft is jammed or an interturn short circuit).

Without a relay, the compressor will either not start at all or will burn out from overload. This is especially true for refrigerators with inverter motorswhere starting currents can reach 5-7 times the nominal values.

Externally, the relay looks like a small plastic box (the size of a matchbox) attached to the compressor housing. Inside it are:

• 🧲 Coil with a core —reacts to changes in current.
• 🔧 Bimetallic plate —bends when heated and opens the contacts.
• 🔄 Contact group — closes/opens the compressor power circuit.

The operating principle of a thermal relay: step-by-step explanation

Let's figure out how the relay controls the operation of a compressor using the example of a typical refrigerator Atlant MXM-1705:

1. Power supply. When the refrigerator is turned on, current flows to the relay coil. The core retracts, closing the starting winding of the compressor.
2. Starting the motor. The rotor begins to rotate, but for the first 1-2 seconds the current in the windings exceeds the rated current by 3-5 times (the so-called starting current).
3. Stabilization of operation. After the rotor accelerates, the current drops, the core releases the starting winding, and the motor operates normally mode.
4. Overheating control. If the current suddenly increases (for example, due to bearing wear), the bimetallic plate heats up and opens the circuit in 5-20 seconds this saves the windings from melting.

Modern models (for example, Samsung RB30J3000WW) are used combined. relaythat combine the functions of a starting and protective device. They are more compact, but also more difficult to diagnose.

What is "operation current"?

This is the maximum current value at which the relay opens the circuit. For household refrigerators, it is usually 1.2–1.5 of the rated current of the compressor. For example, if the motor consumes 1.2 A, the relay will operate at 1.8–2.0 A.

⚠️ Attention: In refrigerators with a system No Frost the relay may operate more often due to the increased load on the compressor during defrosting. This is normal if the interval. between shutdowns at least 10 minutes.

Signs of a malfunctioning thermal relay: when to sound the alarm

How to understand that the problem is in the relay, and not in the compressor or thermostat. Pay attention to the following symptoms:

• ❄️ Refrigerator does not turn on at all —there is no sound of the motor running, the light inside is on.
• 🔄 Compressor starts up and immediately turns off (with a characteristic click) - the cycle is repeated every 5–30 seconds.
• 🔥 Relay housing hot to the touch (more than 60°C) even after 10 minutes of inactivity.
• ⚡ When turned on, you can hear motor humming, but there is no rotation - the relay cannot “push” the rotor.
• 🕒 The refrigerator works a few minutes and turns off, then repeats the cycle (typical for "stuck" contacts).

If at least one of these signs is present, the relay needs to be checked first. In 60% of cases, it is the one that is to blame for the “imaginary” breakdown of the compressor.

How to check a thermal relay with a multimeter: step-by-step instructions

For diagnostics, you will need a multimeter (even a budget model is suitable DT-830B) and a screwdriver. Follow the algorithm:

Disconnect the refrigerator from the network|Remove the back cover (if the relay is hidden)|Take a photo of the wiring diagram|Mark the wires with a marker (if there are more than 3 of them)-->

1. Remove. relay from the compressor, disconnecting the terminals. Usually it is secured with latches or one screw.
2. Ring the contacts:
   • 🔌 Between the terminals 3 and 4 (or S and M on some models) there should be resistance 0 Ohm —these are normally closed contacts.
   • 🔌 Between 1 and 2 (L and T) - resistance infinity (open).
3. Check the coil:
   • 🔧 Measure the resistance between 1 and 3 - it should be in limits 10–50 Ohm (for exact values, see the table below).
   • 🔧 If the resistance 0 Ohm is a short circuit, if infinity — open.

Trigger test:

• 🔥 Connect the relay to the network via a 220V light bulb (for safety).
• 🔥 Heat the relay body with a hair dryer - a working device should open the contacts in 10-30 seconds.

Relay model	Coil resistance (Ohm)	Trigger current (A)
Danfoss 103N0016	15–20	1.8–2.2
Embraco EGX 100	25–35	1.5–1.9
Secop (ex Danfoss) 103N0210	10–15	2.5–3.0
LG Inverter	40–60	1.0–1.4

⚠️ Attention: If during inspection you find that the contacts 3–4 open even in a cold state - the relay is faulty and must be replaced. Do not try to “fix” it by bending the plate: this is a temporary solution that will lead to breakdown of the compressor.

Typical breakdowns of thermal relays and their causes

According to statistics from service centers, 80% of relay failures are associated with four problems:

• 🔥 Overheating of the bimetallic plate —occurs due to prolonged operation of the compressor at maximum currents (for example, when a freon leaks or a clogged capillary tube).
• 🔌 Oxidation of contacts —leads to an increase in contact resistance and false alarms. Often found in refrigerators operating in damp rooms.
• 🧲 Interturn closure of the coil —the relay either does not work at all or “sticks” in the closed state.
• 💥 Mechanical wear —over time, springs and levers lose elasticity, which leads to failure of the protection.

Interesting fact: in refrigerators Samsung with inverter compressors, the relay fails 2 times more often than in conventional models. This is due to the fact that inverters operate on alternating currents, which accelerates the wear of the bimetallic plate.

How to replace a thermal relay with your own hands: instructions with photos

Replacing a relay is one of the few operations that can be performed without special tools. You will need:

• 🔧 Phillips screwdriver (or Torx for some models).
• 📸 Telephone for photographing the connection diagram.
• 🔍 Multimeter for checking the new relay before installation.

Step-by-step instructions:

1. Disconnect the refrigerator from the network and wait until the capacitor is discharged (5-10 minutes).
2. Remove the back cover (if the relay is hidden) or simply disconnect it from the compressor.
3. Take a photo of the wire connection —even if you are sure that you will remember the diagram, a photograph will save you from mistakes.
4. Disconnect the terminals and remove the relay from the mount. In some models (Indesit, Ariston) it is fixed with a latch - carefully pry it off with a screwdriver.
5. Install a new relay, connecting the wires according to the photo. Pay attention to the markings of the terminals:
   • 🔌 L —phase (power).
   • 🔌 T —output to the compressor.
   • 🔌 S —starting winding.
   • 🔌 M —working winding.

Check the operation —turn on the refrigerator and make sure that the compressor starts without clicks or buzzing.

The cost of a new relay varies from 600 to 3000 rubles, depending on the model. For refrigerators Atlant and Biryusa inexpensive analogues Danfoss 103N0016 or Ranco K59are suitable. For LG and Samsung with inverter motors you will have to buy original parts.

⚠️ Attention: If after replacing the relay the compressor still does not start, check the starting resistance (ring between the terminals S i M — the resistance should be 20–50 Ohms). Its breakage is a common cause of a “dead” motor.

Frequently asked questions about thermal relays of refrigerators

Is it possible to repair a relay with your own hands without buying a new one?

Theoretically, yes, but this is a temporary solution. For example, if the problem is oxidized contacts, they can be cleaned with sandpaper (1000–1200 grit). However, in 90% of cases this gives an effect for 1–3 months, after which the relay fails again. It is useless to bend the bimetallic plate: it will lose calibration, and the relay will operate either too early or too late.

The only case when repairs are justified is mechanical damage to the housing (cracks, chips). It can be restored with epoxy glue if the internal parts are in good condition.

How to choose an analogue relay if the original one is not on sale?

Main selection criteria:

1. 🔌 Operation current —must match the rated current of the compressor (indicated on the motor nameplate).
2. 🔧 Mounting type —relays come with latches, screws or clips.
3. 📏 Dimensions —the new relay must physically fit in the place of the old one.
4. 🔄 Connection diagram —check the location of the terminals (L, T, S, M).

For refrigerators Stinol and Atlant relays are suitable Danfoss 103N0016 or Ranco K59-L2450. For inverters - only original ones. several: LG with inverters - only original ones LG 6871JJ2002A.

Why does a new relay activate immediately after installation?

There may be several reasons:

• ⚡ Incorrect connection —terminals are mixed up S and M (starting and operating windings).
• 🔥 Stuck compressor —if the motor shaft does not rotate, the current increases sharply, and the relay turns off the power.
• 🧲 Current mismatch —the new relay is designed for less current than the compressor consumes.
• 💡 Fault to the housing —if the compressor “breaks through” the metal case, the relay operates as protection.

First, check the connection diagram, then measure the compressor current with a multimeter (in ammeter mode). If it exceeds the rated one by more than 20%, the problem is in the motor.

How long does a thermal relay last and how to extend its life?

The average service life of a relay is 5–10 years, but it greatly depends on operating conditions:

• 🌡️ Ambient temperature —at +30°C indoors, the relay wears out 2 times faster.
• ⚡ Electrical network quality —frequent power surges destroy the bimetallic plate.
• 🔄 Frequency of compressor switching on —if the refrigerator is opened every 10 minutes, the relay operates in extreme mode.

To extend the life of the relay:

• 🔌 Use voltage stabilizer (especially relevant for cottages and old houses).
• 🧊 Do not place the refrigerator next to the stove or battery - overheating accelerates wear.
• 🕒 Defrost the refrigerator every 6 months (even if it has No Frost).

Is it possible to temporarily operate the refrigerator without a relay?

Absolutely not. Without a relay, the compressor loses protection from:

• 🔥 Overheating of the windings (leads to an interturn short circuit).
• ⚡ Short circuit (can cause a fire).
• 💥 Shaft jamming (the motor will burn out in 5-10 minutes).

If the relay is broken and a new one is not at hand, it is better to transfer the products to cooler bag or to neighbors, rather than risk costly repairs.