Many owners of household appliances are faced with a situation where the refrigerator stops freezing, and the compressor either does not turn on at all or makes a characteristic humming sound and turns off immediately. In an attempt to understand the cause of the breakdown, users often come across the term “pilot” or “start relay”. This small but critical element is responsible for the startup and safe operation of the motor-compressor, without which refrigerant circulation in the system is impossible.
In fact, start-protective relay (this is the technically correct name for this unit) is the connecting link between the electrical network and the refrigerator motor. It provides a starting pulse to overcome rotor inertia and instantly cuts off power in the event of overload or overheating. Understanding the principle of its operation helps not only to correctly diagnose a malfunction, but also to avoid more expensive repairs of the main unit.
In this article we will analyze in detail the design of various types of relays, consider the symptoms of their failure and determine whether it is possible to replace it yourself. Induction relay and the posistor model have fundamental differences in designs, which affects the methods of their verification. Knowledge of these nuances will allow you to save time and money when servicing equipment.
The principle of operation of the starting mechanism in the compressor
The main task of the pilot is to create conditions for the start of the asynchronous compressor motor. At the moment of switching on, a magnetic field appears in the motor windings, but an additional shear pulse is required to start rotating the rotor. It is starting winding, activated through a relay, that creates the necessary torque. As soon as the engine reaches operating speed, there is no need for this winding, and it should be immediately turned off.
In parallel with the starting function, the device acts as a safety guard. Inside the housing there is a thermal release that responds to current strength. If the compressor tries to start, but the rotor is stuck, or if the load on the network exceeds the norm, the current increases sharply. The bimetallic plate inside the relay heats up, bends and opens the circuit, preventing the expensive motor windings from burning out. Cricially, the circuit opens a fraction of a second before the temperature of the windings reaches a critical value that destroys the insulation.
The process of starting and stopping occurs cyclically and automatically. During normal operation, the cycle takes a few seconds: applying voltage, triggering the trigger, accelerating the rotor, disconnecting the starting winding and returning to normal operation. If a malfunction occurs in the system, the cycle is interrupted at the protection stage, and the refrigerator goes into standby mode until the thermocouple cools down.
Design features of induction and posistor relays
In the household appliances market, there have historically been two main types of starting devices, which differ significantly in their internal structure. The first to appear were induction (electromagnetic) relays. Their work is based on the physical movement of the core inside the coil. When current passes through the coil, the created magnetic field draws in the core, which mechanically closes the contacts of the starting winding.
With the development of electronics, posistor (thermal) relaysappeared. Their design has no moving mechanical parts in the classical sense. The main element here is a posistor - a ceramic element whose resistance increases sharply when heated. When voltage is applied, the posistor is cold and passes current to the starting winding. Heating up from the passing current, it almost completely blocks it, performing a shutdown function. Posistor models They are considered more reliable and less susceptible to wear from vibration.
Visually distinguish them also easy. Induction relays often have a more massive body and contain a copper coil and a movable rod inside. PTC devices are usually more compact, lighter and contain a tablet or disk made of special ceramics inside. Modern refrigerators, such as Indesit, Atlant or Beko, are often equipped with posistor options due to their durability and low production cost.
Can an inductive relay be molded onto a posistor one?
In most cases, direct replacement is impossible without modification electrical circuit. Induction relays operate with a certain operating current, while posistor relays require a starting capacitance or a specific circuit for connecting the windings. Installing the wrong type of relay can lead to instantaneous combustion of the new component or damage to the compressor.
Typical symptoms of a faulty starter device
Diagnostics of the breakdown often begins with an analysis of the behavior of the refrigerator. If you hear the motor humming for a few seconds, then a clicking sound and then silence, this is a classic sign of a problem in the starting circuit. After some time (from 5 to 20 minutes), the cycle may repeat. This means that thermal relay is triggered by an overload, since the engine cannot reach operating mode.
There are a number of signs that are highly likely to indicate a pilot defect:
- 🔊 The compressor makes a loud click when trying switch on, but does not start.
- 🔥 The relay or compressor housing gets very hot in the lower part of the refrigerator.
- 💡 The light inside the refrigerator is on, but no cold is generated, which indicates the operation of the electrical network, but not the unit.
- 👃 The appearance of a burning or melted smell plastics in the engine compartment area.
It is important to note that similar symptoms can be observed with an interturn short circuit in the windings of the compressor itself. Therefore, visual inspection and testing with a tester are mandatory steps before purchasing a new part. If after replacing the relay the situation repeats, the problem lies deeper - in the mechanical part of the motor or in the windings.
⚠️ Attention: If after clicking and turning off the compressor hums very loudly and aggressively, do not try to start it repeatedly. This may indicate a wedge in the piston group, and further attempts to turn on will only finish off the engine completely.
Methods of diagnostics and performance testing
To carry out high-quality diagnostics, you will need a multimeter and a minimum set of tools. The first step is to turn off the power to the refrigerator and remove the relay from the compressor. Usually it is fixed on three contacts and clamped with a metal bracket or plastic latches. Remove the protective box and remove the device.
The posistor element is checked by measuring the resistance. When cold, it should be several tens of ohms (usually from 10 to 60 ohms, depending on the model). If the multimeter shows infinity or, conversely, zero, the element is faulty. Also carefully inspect the housing for cracks, and the inside for traces of burning or melting of the contacts. Visual defect Ceramics are often visible to the naked eye.
Induction relays are checked a little differently. It is important to check the mobility of the core here. It should move freely inside the coil and return to its original position under the influence of gravity. If the core is stuck or covered with oxides, the relay will not work correctly. The coil resistance should be minimal, close to zero, which indicates the integrity of the winding.
☑️ Relay diagnostics
Comparative table of relay characteristics
To better understand the difference between types of devices and choose the right replacement, it is worth turning to a comparative analysis of their parameters. Different compressor models require relays with specific current and response time characteristics.
| Parameter | Induction (Electromagnetic) | Posistor (Thermal) |
|---|---|---|
| Operation principle | Electromagnetic core retraction | Change in resistance when heated |
| Presence of moving parts | Yes (core, contacts) | No (solid-state element) |
| Vibration sensitivity | High (contacts may stick) | Low (monolithic design) |
| Cooling time before restarting | Instant (depending on the bimetal) | It takes time for the posistor to cool down |
| Typical resource | Medium | High |
When choosing a replacement part, pay attention to the markings. Numbers and letters stamped on the housing indicate compatibility with certain series of compressors. For example, marking RTK or R-3 is often found on old Soviet and post-Soviet models, while PTC is on modern imported units.
Replacement process and precautions
Replacing the pilot is one of the few operations that can be done at home if you have basic electrical skills. The main rule is complete safety. Make sure the power cord is removed from the outlet. Any manipulations with live electrical components are strictly prohibited.
Carefully remove the old relay, remembering or photographing the position of the wires. Often the wires are simply inserted into the terminals, but they can also be soldered. If soldering, use a soldering iron with enough power to quickly heat the contact without damaging the wire insulation. The new relay is installed in a strictly defined position, usually marked with an arrow UP or TOP. This is especially important for induction relays, where the core must fall under its own weight.
After installation, reassemble the structure in the reverse order, secure the protective casing and turn on the refrigerator. For the first 10-15 minutes, it is advisable to check the operation: the motor should start, run and turn off when the temperature is reached, or operate normally. If you hear any extraneous sounds or repeated clicks, the device must be turned off immediately.
The influence of external factors on service life pilot
The service life of the starting protection device depends not only on its quality, but also on the operating conditions of the refrigerator. Frequent power surges are the main enemy of electronics and electricians. Sudden changes can lead to spark travel on the contacts or thermal overload, even if the compressor itself is working properly.
Ventilation of the engine compartment is also critical. If the refrigerator is installed close to the wall, and dust and animal hair have accumulated behind it, heat from the compressor is not removed effectively. Overheating leads to more frequent operation of the thermal protection and accelerated aging of the relay materials. Regular cleaning of the space behind the refrigerator prolongs the life of all its components.
Humidity is another hidden factor. In conditions of high humidity (for example, in a kitchen with poor ventilation or in a private home), the contacts may oxidize. Oxides increase resistance, which causes additional heating and can lead to false protection activations or, conversely, to sticking of contacts.
⚠️ Attention: Technical characteristics and markings of relays may vary between different manufacturers. Before purchasing a new part, check the spare part code with the documentation for your refrigerator or with a consultant in a specialized store, since there are no universal solutions.
Frequently asked questions (FAQ)
Is it possible to temporarily start a refrigerator without a relay?
Theoretically, it is possible to apply voltage directly to the windings, but doing this is strictly not recommended without special knowledge and equipment. You risk burning out the compressor windings in seconds as there will be no overload protection. In addition, without a starting mechanism, the engine may not pick up speed and simply hum, consuming a huge current.
Why does a new relay burn out immediately after installation?
This may indicate a malfunction of the compressor itself (interturn short circuit, wedge), a short circuit in the refrigerator wiring, or unstable voltage in the network. It is also possible that a relay has been selected with unsuitable operating current characteristics for a given motor model.
How to determine which direction to place the relay?
On the body of almost all relays there are markings in the form of an arrow and inscriptions UP, TOP or UP. This side should face straight up. For induction relays it is critical that the core can move freely. For posistor devices, the orientation is less critical, but it is better to follow the markings for proper heat dissipation.
How long does a starting relay last on average?
The average service life of a high-quality relay is 7-10 years, which coincides with the average life of a compressor. However, with frequent power surges or overheating of the engine compartment, it may fail much earlier, after 3-4 years of operation.