When in the operating instructions or in a conversation with The master sounds the word “posistor”, many owners of household appliances are perplexed. This component often remains in the shadows, although it is the one that ensures the safe start of the compressor engine. Understanding a posistor is for a refrigerator that and what role it plays is necessary for correct diagnosis of breakdowns. Without this element, starting the refrigerator would be impossible or would be accompanied by a high risk of failure of the motor windings.
In fact, we are talking about the key element of the starting relay, which is responsible for switching the operating modes of the starter. If your refrigerator stops turning on or makes a humming noise without starting, the problem often lies in this small ceramic disc. In this article we will analyze in detail the device, principle of operation and testing methods PTC resistorso that you can independently assess the state of the equipment.
Main purpose and principle of operation
A posistor is a semiconductor device, the resistance of which increases sharply when heated. When the refrigerator is connected to the network, a starting current passes through the windings of the electric motor, which significantly exceeds the operating current. It starting current creates the necessary magnetic field to spin the rotor. A posistor in a cold state has low resistance and allows current to flow freely through the starting winding.
As soon as current begins to flow through the part, it heats up. This process takes a split second. When a certain temperature (Curie point) is reached, the resistance of the posistor increases abruptly to several megaohms. In fact, it turns into an insulator and opens the starting winding circuit. The engine continues to operate on the main operating winding, consuming normal current.
⚠️ Attention: Do not try to start a refrigerator with a faulty or removed posistor by connecting the starting winding directly. This will lead to overheating and burning of the compressor windings in a matter of minutes.
This circuit avoids the use of mechanical contacts that could stick or spark. Thermistor works silently and reliably if it is in good condition. After turning off the power, the refrigerator must cool down so that the posistor cools down and reduces its resistance again, preparing for the next startup cycle.
Design features and location
Externally, the posistor looks like a small gray or black tablet enclosed in a plastic housing of the starting relay. It is tightly connected to the bimetallic strip or contacts. The design is designed to operate under conditions of vibration and temperature changes characteristic of the compressor compartment.
The location of the element is standard for most refrigerator models Indesit, Beko i Atlant. It is located at the rear of the unit, directly on the compressor. To access it, you don’t always need to remove the entire refrigerator - sometimes just moving it away from the wall is enough. However, for a full replacement, you will need to remove the protective casing.
Main characteristics that you should pay attention to when selecting an analogue:
- 🔹 Nominal resistance at room temperature (usually from 4 to 50 Ohms).
- 🔹 Maximum permissible load current.
- 🔹 Geometric dimensions and type of contact fastening.
- 🔹 Switching temperature threshold.
It is important to understand that it is almost impossible to visually determine the serviceability of a part. There may be cracks in ceramics, but most often the defect is hidden within the structure of the material. Therefore, when repairing, they rely on measurements with a multimeter or the exclusion method.
Symptoms of a faulty starting relay
You can determine what starting device has failed by its characteristic signs. Most often, users notice that the refrigerator is humming, but the compressor does not start. After a few seconds, a click is heard and the humming stops. This triggers the thermal protection relay, seeing that the current does not drop, since the starting winding has not turned off or turned on.
Another option is complete silence. When plugged in, no sounds are heard, the light in the chamber is on, but there is no cold. This may mean that the posistor is “broken” and the current simply does not reach the starting winding. It is also possible that the compressor itself overheats, as it tries to start, but cannot turn the shaft without an additional impulse.
| Symptom | Probable cause | Action |
|---|---|---|
| Humming and clicking | Sticking contacts or breakdown of the posistor | Replacing the relay |
| No reaction | Open circuit of the posistor | Checking with a multimeter |
| Smell burning | Overheating of wiring or relay | Urgent repair |
If you notice that the refrigerator does not turn on the first time, but after several attempts, this is also an alarming signal. Wear PTC element leads to a change in its temperature characteristics, and it stops switching modes on time.
Diagnostics and testing with a multimeter
For accurate diagnostics, you will need a regular digital multimeter. Before starting work, make sure that the refrigerator is unplugged. Remove the back cover of the compressor and carefully remove the starting relay along with the posistor. Usually they are connected into a single unit.
Switch the multimeter to resistance measurement mode (Ohm). Connect the probes to the posistor contacts. If the device shows resistance within the normal range (usually this value is indicated on the case, for example, 15 Ohms or 22 Ohms), then the element is cold and probably intact. If the multimeter shows infinity (one in the most significant digit), then there is a break inside.
☑️ Checking the posistor
The difficulty of checking is that the posistor is checked only in a cold state. If you just turned off the refrigerator, it may be hot and show high resistance, which is normal for a warm state, but a diagnostic error. Allow the part to cool for at least 15-20 minutes at room temperature.
⚠️ Attention: Do not use the power source (outlet) directly for testing. Applying voltage to a faulty posistor can lead to a short circuit or fire.
It is also worth checking the wires going to the relay. Often the problem lies not in the part itself, but in oxidized contacts or a broken wire. Clean the contacts if plaque is visible on them.
Replacement process and selection of analogues
If the diagnostics showed a malfunction, the only correct solution is replacement. Repair of the posistor is impossible, since it is a disposable element. To replace, you will need to buy a new starting relay assembly or a separate posistor, if you know how to solder it or attach it to an old case.
When purchasing, pay attention to the markings. Numbers on the case, such as PTC 15Ω or R-6indicate resistance. Using a posistor with an inappropriate resistance will either result in the impossibility of starting engine, or to its overheating. It is best to take an original part or a high-quality universal analogue suitable for the power of your compressor.
Procedure for replacement:
- Remove the old relay, remembering the position of the contacts.
- Install a new posistor or the entire relay block on the compressor rod.
- Connect the wires according to the diagram (usually they are color coded).
- Secure the casing and turn on the refrigerator.
Can I use a relay from another refrigerator?
Yes, if the compressor power and connection type match. However, it is better to select according to the catalog number or technical characteristics of the resistance.
After replacement, the refrigerator should start with a characteristic sound and after a few seconds go into operating mode without buzzing. If the problem persists, the compressor itself or the turn-to-turn short circuit of the windings may be faulty.
Common mistakes during self-repair
The most common mistake is ignoring the cooling time. Trying to check or start the refrigerator immediately after several unsuccessful attempts to turn it on will lead to nothing. The posistor must cool down to return to low resistance. In a hurry, technicians often make a false conclusion that the compressor is broken.
Another mistake is the use of inappropriate materials for insulation or fastening. Some people try to glue the posistor with superglue, which is unacceptable. The adhesive may flow in or melt, changing thermal characteristics. Use only standard latches or heat-resistant materials.
Also, do not neglect cleaning the contacts. Oxides on copper contacts create additional resistance, which can confuse diagnostics. Wipe the contacts with alcohol or a special cleaner before installing a new part.
The effect of voltage surges on the posistor
It is worth mentioning that a common cause of failure is building starter element are voltage surges in the network. Sudden changes can pierce the ceramics or change its structure. If the lights flicker frequently in your home or there are problems with the power supply, it is recommended to install a voltage stabilizer.
This will protect not only the refrigerator, but also other expensive equipment. The posistor takes the first shock at start-up, and replacing it is cheaper than repairing or replacing the compressor. Regular preventative maintenance and careful attention to the sounds of a running refrigerator will help avoid serious breakdowns.
In conclusion, a posistor is a small but critical element in the starting system of your refrigerator. Understanding how it works allows you to quickly diagnose problems and avoid unnecessary expenses on calling a technician for simple operations. Keep an eye on the condition of your equipment, and it will serve you for many years.
How to extend the life of the starting relay?
Avoid turning the refrigerator on and off frequently. Let the compressor stop completely and cool down before starting again (at least 3-5 minutes).
Is it possible to start a refrigerator without a posistor?
No, starting without a posistor is impossible for most household refrigerators. The engine will hum but will not start, which will quickly cause it to burn out. A posistor is necessary to create the initial torque.
How much does it cost to replace a posistor?
The cost of the part itself is low and usually ranges from 200 to 800 rubles, depending on the model and manufacturer. The work of a replacement technician can cost from 1000 rubles, but the process is simple and is often done independently.
Why does the refrigerator click and not turn on?
The click is the sound of the thermal protection relay operating. It cuts off the power because the motor is drawing too much current and will not start. The reason is most often a faulty starting relay (posistor) or a jammed compressor.
How to determine the resistance of a posistor?
The resistance is indicated on the body of the part (for example, 15 Ohm, 22 Ohm, 33 Ohm). You can measure it with a multimeter in a cold state. A slight deviation from the nominal value is allowed, but not a break or short circuit.