Sudden stoppage of the compressor or a characteristic click followed by silence often indicates a failure of the starter relay This small but critical element is responsible for starting the electric motor of the refrigeration unit, providing a short-term voltage supply to the starting winding. If the relay is faulty, the motor hums, but does not start, or does not respond at all to thermostat commands, which can ultimately lead to defrosting of food and damage to equipment.
Diagnostics of this unit does not require complex professional equipment and is quite within the capabilities of a home handyman with basic electrical skills. In this article we will analyze in detail the design of various types of relays, the algorithm for checking them with a multimeter and visual inspection, which in 80% of cases allows you to identify a defect without additional measurements.
Before proceeding with disassembly, you need to understand that starting relay is a consumable material, the resource of which is limited by the number of switching cycles. Frequent voltage drops in the network significantly reduce its service life, so timely checking can save the compressor from more serious damage, such as an interturn short circuit or a wedge of the piston group.
Signs of a faulty starting device
You can identify the problem even before removing the part by paying attention on the behavior of the refrigerator. Most often, a breakdown manifests itself in a cyclic repetition of the same actions: the unit turns on, a loud click is heard, the motor hums for several seconds, followed by a click and shutdown again. This is a classic symptom that starting winding does not receive the necessary impulse or the switching mechanism is jammed.
In some cases, the malfunction is accompanied by a specific burning smell or smoke from the back of the housing where the compressor is located. This may indicate that the contacts inside the relay have burnt out and are starting to melt the plastic housing, creating the risk of a short circuit. If you notice such signs, you should immediately stop using the refrigerator.
Another indirect sign is heating of the compressor housing when the fan is not working (in No Frost models) or there is no cold in the chambers. The motor may try to start by drawing high current, but due to the lack of rotor rotation, the thermal protection quickly trips, breaking the circuit. In such situations thermal relay performs its protection function, but requires replacement of the starting element.
Types of starting relays and their design
On the modern market and in older models of refrigerators, there are two main types of starting devices: induction (electromagnetic) and posistor. Induction relays work on the principle of an electromagnet: when current is supplied, the core is retracted, closing the contacts of the starting winding, and when the speed increases, the current drops and the spring opens the circuit. They are often marked RTP, RTK, RT.
Posistor relays (marking P-1, P-2, PTC) are more modern and do not have moving mechanical parts. Inside them there is a heat-sensitive element - a posistor, which, when heated by current, sharply increases its resistance, actually breaking the starting winding circuit. Such devices are considered more reliable, but are sensitive to current overloads.
You can visually distinguish them by their internal structure: in induction relays you can see a coil and a movable core, and in posistor relays you can see a tablet of ceramic material and a contact group. Understanding the type of device is important for correct diagnosis, since the methods for testing them may differ slightly, especially when assessing resistance.
What is the danger of replacing a relay with an analogue of a different type?
Replacing an inductive relay with a posistor (or vice versa) without changing the connection diagram can lead to burnout of the motor windings. Induction relays require an exact match of the release current with the characteristics of the motor, while posistor relays operate based on heating time. Always select a replacement strictly according to the catalog number or technical parameters of the original.
Preparation for diagnostics and safety measures
The first and most important stage of any diagnosis is to completely disconnect the refrigerator from the power supply. Unplug the cord from the outlet and make sure there is no voltage at the plug. Working with electrical appliances under load is strictly prohibited and may result in electric shock or damage to the multimeter.
You will need access to the rear of the unit to carry out work. Move the refrigerator away from the wall to provide easy access to the compressor. Typically the start relay is mounted on the side or top of the motor and covered with a plastic casing that must be removed. You will need a flathead screwdriver to remove the housing latches and, possibly, pliers.
The main testing tool will be multimeter (tester). Make sure that the device is in working order, the batteries are charged, and the probes have no insulation damage. Switch the multimeter to resistance measurement mode (Ohms), selecting a limit of 200 or 2000 Ohms, depending on the model of the device. Also prepare a container for soaking parts if you need to clean the contacts from carbon deposits.
☑️ Checking readiness for repair
Visual inspection and dismantling of the relay
After removing the protective casing, carefully disconnect the relay from the compressor contacts. It usually simply slides onto the three motor pins and is secured with a bracket or clamp. Do not use excessive force to avoid breaking the plastic mounting ears or damaging the wires going to the terminals.
Carefully inspect the relay housing from all sides. The presence of melting, cracks, blackening or traces of soot indicates that a breakdown or overheating has occurred inside. If the relay body is swollen or deformed, further inspection may be impractical - the part definitely requires replacement.
Shake the relay near your ear. If you hear a clear knocking or ringing of parts coming off inside, this is a bad sign. In induction relays, the core can fall apart, and in posistor relays, the ceramic element can crumble. The integrity of the internal structure is critical to the proper operation of the trigger mechanism.
⚠️ Attention: When dismantling, note or photograph the position of the wires. Reversed polarity or connecting wires to the wrong contacts can lead to a short circuit immediately after turning on the refrigerator.
Checking the relay with a multimeter: step-by-step instructions
Diagnostics with a multimeter allows you to determine the condition of the internal circuits with high accuracy. For induction relays, it is necessary to ring the coil and check the mobility of the contacts. The coil resistance is usually several tens of ohms (from 10 to 50 ohms depending on the model). If the device shows one (open) or zero (short circuit), the relay is faulty.
Checking a posistor element requires taking into account its temperature characteristics. At room temperature, the posistor resistance should be low (20–50 ohms). However, in order to check its operation in dynamics, the element must be heated (for example, with a hairdryer) and the resistance must be re-measured - it should increase to thousands of Ohms (break mode). If the resistance does not change when heated, the posistor has “died.”
Pay special attention to checking the contacts for short circuits. In normal condition (relay removed from the motor and inverted), the starting winding contacts should be open for the induction relays. If the tester shows a short circuit between the contacts at rest, it means that the mechanism is stuck and requires replacement or complex cleaning.
Table of normal resistance values
The following are approximate resistance values for various types of relays. Remember that specific numbers may vary depending on the manufacturer and model of the refrigerator (Indesit, Atlant, Bosch, LG).
| Relay type | Test element | Normal resistance (Ohm) | Fault symptom |
|---|---|---|---|
| Induction (RTK, RTP) | Coil | 10 - 50 Ohm | Open (1) or short circuit (0) |
| Induction (RTK, RTP) | Contacts (rest) | Infinity | Short circuit (0 Ohm) |
| Posistor (PTC, R-1) | Posistor (cold) | 20 - 60 Ohm | Values out of range |
| Posistor (PTC, P-1) | Posistor (heated) | > 1000 Ohm (kOhm) | Remains low |
| Thermal protection | Bimetallic strip | 0 - 1 Ohm | Open circuit |
If your measurements differ radically from the data in the table, there is a high probability of a part defect. However, it is worth taking into account the error of the measuring device itself and the quality of contact of the probes with the relay terminals. Before the final output, clean the contacts with an eraser or alcohol.
Cleaning contacts and restoring functionality
In some cases, the relay can be restored if its failure is caused by oxidation of the contacts or moisture. To do this, carefully open the case (if the design allows it) or get to the contact group. Clean the contacts with fine sandpaper or a file until they have a metallic shine.
Remove carbon deposits and soot using a cotton swab soaked in alcohol or a special contact cleaner (Contact Cleaner). It is important not to bend live parts or disrupt the geometry of moving elements. After cleaning, reassemble the relay and check the ease of movement of the moving parts.
However, if the cause of the malfunction is burnout of the contact metal or degradation of the posistor, cleaning will not help. In such cases, a complete replacement of the unit is necessary. Repair by installing jumpers is strictly not recommended, as this will damage the compressor windings.
⚠️ Attention: Do not use aggressive solvents such as acetone or gasoline inside the plastic relay housing to clean the contacts. They can dissolve the plastic or damage the coil insulation, which will lead to a new breakdown.
Relay replacement and final assembly
If the check shows a malfunction, purchase a new analogue. When purchasing, pay attention not only to the markings, but also to the orientation of the contacts and the method of attachment. Install the new relay onto the compressor pins, making sure that it is seated tightly and all the way.
Connect the wires to the terminals according to the previously made diagram or photograph. Check that all connections are secure. Install the relay into the protective housing and secure it to the compressor. Make sure that the wires do not touch hot parts of the motor or moving elements (if there is a fan).
Plug in the refrigerator and listen. Startup should be smooth, without loud clicks or buzzing. The compressor should pick up speed and operate evenly. If after 10-15 minutes of operation the motor does not heat up excessively and cold begins to appear in the chambers, the repair can be considered successful.
What to do if the new relay also does not start the compressor?
If replacing the relay did not help, the problem may be deeper. Possible reasons: an interturn short circuit in the motor windings, a wedge in the compressor piston group, or a malfunction of the motor itself. In this case, professional diagnostics are required by measuring the starting current and winding resistance directly.
Frequently asked questions (FAQ)
Is it possible to temporarily start a refrigerator without a starting relay?
Theoretically, you can start the motor by applying voltage directly to the starting winding, but doing this manually is extremely difficult dangerous and not recommended. This can lead to burnout of the windings due to the lack of automatic shutdown of the starting phase. In addition, this will not solve the problem of cyclic switching, but will only create an emergency situation.
Why does the starting relay burn out?
The main reasons for failure are power surges in the network, frequent power outages, aging of materials (posistor or springs) and overheating of the compressor due to contamination of the capacitor. Also, the relay can burn out if the compressor itself is “heavy” to start (stiff piston movement).
Will a relay from another refrigerator be suitable?
The relay is selected not by the brand of the refrigerator, but by the power and type of compressor. It is important that the operating current and overall dimensions match. Using the wrong relay may result in it not opening the circuit (the compressor will burn out) or not closing it (the compressor will not start).
How much does it cost to replace the starting relay?
The cost of the relay itself usually ranges from 300 to 1500 rubles, depending on the model and manufacturer. If you do the replacement yourself, this is the only cost. The services of a repairman will cost more, including diagnostics and travel.