When No Frost refrigerator the cooling stops and food in the freezer begins to melt, the first thought is that the compressor has failed. However, often the culprit of the breakdown is a much simpler and cheaper part - a thermal protection relay. It is this component that is responsible for the safe start of the engine and protection of the windings from overheating. If you notice that the unit hums, but does not start, or turns on only for a few seconds and goes silent, diagnosing the protective device becomes the first step to restoring the equipment's performance.
Modern systems No Frost place high demands on the stability of the compressor, since it depends on refrigerant circulation and operation of blowing fans. Start-up protection relay in such models it works in tandem with a starting capacitor or works as a single unit, providing the necessary phase shift to start the rotor. Understanding the principle of operation of this unit will allow you to independently determine the nature of the malfunction and avoid an expensive call to a technician for a simple replacement of the part.
In this article we will analyze in detail the design of the protective mechanism, consider the symptoms of its failure and provide step-by-step instructions for checking the serviceability using a multimeter. You don't need to be a professional electrician to perform an initial diagnosis, but safety precautions and accurate measurements are critical. We will also touch on issues of compatibility of parts for different brands, such as Indesit, Atlant or LG.
The principle of operation and the design of the protective mechanism
Thermal relay in the design of the refrigerator performs a dual function: it ensures the initial start of the engine and protects it from overcurrent. Inside the plastic case, which fits directly onto the contact group of the compressor, there are two main parts - a starting relay and thermal protection. The starting device is an electromagnetic coil or posistor that closes the circuit of the starting winding at the moment of start.
The second element is thermal protectionworking on the principle of a bimetallic plate. At normal current, the plate is in a closed state, allowing electricity to flow to the motor windings. If the current exceeds the permissible values or the compressor housing heats up above a critical point (usually around 135°C), the bimetallic strip bends and opens the circuit. This action turns off the power, preventing the motor windings from burning out.
After cooling, the plate returns to its original position and the cycle repeats. In systems No Frost this process occurs automatically, but frequent on-off cycles may indicate a problem. If the relay “clicks” every few minutes, and the refrigerator does not cool, it means that the protection is triggered due to the impossibility of starting the rotor or a malfunction of the protective element itself.
Visual diagnostics and primary signs malfunctions
Before picking up measuring instruments, it is necessary to conduct an external inspection. Often signs of a malfunction are visible to the naked eye. If you hear a characteristic click, followed by a hum, and then silence, this is a sure sign that protection triggers, preventing the engine from starting. In some cases, you may hear a quiet cracking sound or see sparking in the compressor area when you try to turn it on.
Remove the rear protective panel of the refrigerator to gain access to the motor. Carefully remove the plastic relay cover that fits over the compressor contacts. Pay attention to the condition of the plastic: if it is blackened, melted or has traces of burning, this indicates overheating and breakdown. Also inspect the internal contacts: they should be clean, without oxidation or carbon deposits.
⚠️ Attention: If you find traces of severe melting of the plastic or there is a strong smell of burnt wiring, operating the refrigerator is prohibited until the unit is completely replaced to avoid a fire.
An additional sign may be the condition of the wires going to the relay. If the insulation is cracked or the wires are blackened at the point where they enter the relay housing, then sparking has occurred there. In systems No Frost it is also important to check whether moisture has got inside the relay housing, although this rarely happens if installed correctly.
- 🔊 A characteristic clicking sound every 2-5 minutes without starting the compressor.
- 🔥 Presence of a burning smell or visible traces of soot on details.
- 🧊 The refrigerator has stopped freezing, the light in the chamber is on.
- ⚡ Sparking in the contact area when turned on.
Preparation for inspection and safety precautions
Any work with electrical equipment requires strict adherence to safety rules. Before starting diagnostics, be sure unplug the refrigerator from the electrical network. It is not enough to simply turn it off with a button; you must remove the plug from the socket. This will eliminate the risk of electric shock and damage to the multimeter.
To carry out the work, you will need a minimum set of tools: a screwdriver for removing the casing, pliers and, most importantly, multimeter (tester). Make sure that the device is in working order and its batteries are not discharged. If you are using a dial tester, first calibrate it to zero.
After turning off the power, allow the compressor to cool for 15-20 minutes. The thermal relay must be in a cold state to correctly test its contacts. If the part is hot, the bimetallic plate may remain in an open state, which will lead to false readings when dialing.
☑️ Preparation for diagnostics
Step-by-step instructions: how to test a relay with a multimeter
The testing process involves measuring the resistance between the contacts. Switch the multimeter to resistance (ohm) measurement mode, usually the 200 ohm range. First check the integrity of the thermal protection circuit. Find the contacts going to the bimetallic strip. In a cold state, the resistance between them should be close to zero (usually less than 1 ohm).
If the multimeter shows one or infinity, then the circuit is open and thermal protection faulty. Next, check the start relay. For electromagnetic relays, the coil resistance should be several ohms (typically 3 to 30 ohms, depending on the model). If the resistance is too high or absent, the coil has burned out.
For posistor relays (which are often found in modern models Samsung or Beko) the test is more difficult, since a cold posistor has a low resistance, and when heated it increases sharply. A simple test may show the norm, but the part will not work under load. In such cases, it is better to use the method of substituting a known good analogue.
| Test type | Normal reading | Failure sign |
|---|---|---|
| Thermal protection (cold) | 0 - 1 Ohm | Infinity (open) |
| Starting relay coil | 3 - 30 Ohm | 0 Ohm (short circuit) or infinity |
| Contacts for breakdown | Infinity | Any resistance |
Nuances of testing posistors
A posistor is a semiconductor element whose resistance depends on temperature. When cold, it passes current, closing the starting winding. When current passes, it heats up and becomes a dielectric, breaking the circuit. It is difficult to check its performance with a conventional multimeter, since it only shows a cold state. The best diagnostic method is replacement with a new one.
Analysis of results and selection of replacement
If during the test you find that the contacts do not ring or the coil resistance does not meet the standard, the part must be replaced. Repairing the internal elements of the relay is impossible and does not make economic sense. The cost of a new starting protection device is low, and its replacement takes little time.
When choosing a new part, it is critical to consider the parameters of the compressor. There is always a marking on the relay body, for example, R6, PTC-111 or 10-45M. These codes indicate the range of currents at which the protection operates. Installing a relay with inappropriate parameters can lead to either frequent false shutdowns or combustion of the compressor due to untimely protection.
Pay attention to the type of contact connection. They can be positioned vertically or horizontally, and also have a different number of pins. Refrigerators No Frost often use universal relays that are suitable for various models, but require correct wiring according to the diagram.
Replacement of the part and first start-up systems
The process of installing a new part begins with removing the old one. Carefully disconnect the wires from the contacts, remembering their location. If the wires are oxidized, strip the ends. The new relay is put on the contact group of the compressor until a characteristic click is heard. It is important that it fits tightly and does not dangle.
Connect the wires according to the diagram or color marking. Usually the phase wire goes to the protection input, and the neutral wire goes directly to the winding, but it is better to double-check this with the documentation for the specific refrigerator model. Make sure that all connections are secure and the insulation is not damaged.
After assembly, plug in the refrigerator. In the first seconds you can hear a hum, which after 1-3 seconds will be replaced by the even hum of a working compressor. If the start-up was successful, after 10-15 minutes the condenser (grid at the back) will begin to heat up, which indicates the start of refrigerant circulation.
⚠️ Attention: If after replacing the relay the compressor hums again, but does not start, or the machine in the panel immediately knocks out, the problem may be in the compressor itself (an interturn short circuit or a wedge). Further attempts to start may finish off the motor.
Frequently asked questions (FAQ)
Is it possible to temporarily start a refrigerator without a relay?
Theoretically, you can start the compressor by applying voltage directly to the starting winding, but this is strictly not recommended. Without thermal protection, the compressor will burn out in a matter of minutes if an overload occurs, and repairing the engine will cost much more than replacing the relay.
Why does a new relay burn out after a few days?
Frequent combustion of new relays indicates that the cause of the malfunction is not in the protection itself, but in the compressor. The motor may consume increased current due to wear or problems with the windings, which is why the relay constantly works at the limit and fails.
Is a relay from another brand suitable, for example, from Indesit to Atlant?
Compatibility is determined not by the brand of the refrigerator, but by the parameters of the compressor and the size of the relay. If the markings and current characteristics match, and the mounting location is identical, installation is possible. However, it is better to look for original components or high-quality universal analogues.
How often do you need to change a thermal relay?
The resource of a high-quality relay is designed for the entire service life of the refrigerator (10-15 years). Replacement is required only in case of failure. Frequent power surges in the network can shorten the service life of the part, so it is recommended to use a stabilizer.
Can a relay click if it is working?
In normal operation, a working relay clicks once when starting and once when stopping the compressor (a few minutes after shutdown). If the clicks are repeated frequently (every 10-30 seconds), this is a sign of a malfunction of the starting system or the compressor itself.