Sudden stoppage of the compressor or its humming without starting often indicates a faulty start relay. This small but critical component is responsible for supplying voltage to the motor windings at the moment of starting. If the refrigerator has stopped freezing, and the motor operates intermittently or makes a characteristic click and goes silent, there is a high probability that exactly starting relay has failed. In such situations, a complete replacement of the unit is not required, it is enough to carry out competent diagnostics.
Checking the element allows you to determine whether it needs replacement or whether the problem lies deeper, for example, in the windings of the compressor itself. To carry out the work you will need a minimum set of tools and basic electrical skills. It is important to understand that start-up protection relay (PZR) combines the functions of engine starting and overload protection, so its serviceability directly affects the service life of the entire refrigeration unit.
Before starting disassembly, you need to make sure that the refrigerator is disconnected from the power supply. Any manipulation of live electrical components is strictly prohibited and may result in electric shock or damage to measuring instruments. After turning off the equipment, you can begin to visually assess the condition of the external contacts and prepare the multimeter.
Fault symptoms and preliminary diagnostics
The first sign that starting relay requires checking is the characteristic behavior of the compressor. The engine may try to start, make a loud clicking noise, and then stop immediately. After some time, the cycle repeats. This phenomenon is often called "cyclic firing". In some cases, the motor hums, but the shaft does not turn, which may indicate jamming or a problem with the supply of a starting impulse.
It is also worth paying attention to the temperature regime. If the temperature in the refrigerator and freezer compartments rises and food begins to deteriorate, this is a direct signal that the cooling circuit is malfunctioning. The compressor can operate continuously without shutting down, trying to reach the set parameters, but due to the lack of proper starting of the main shaft, the cooling capacity drops to zero.
⚠️ Attention: If, when operating the refrigerator, you smell burning plastic or see smoke coming from the bottom of the case, immediately unplug the appliance. This may indicate a short circuit in the starting relay circuit or motor windings.
Often the malfunction is accompanied by visual changes. Melting, cracks, or traces of soot may appear on the relay housing. The internal contacts may have oxidized or burned, which increases the contact resistance and interferes with normal current flow. If, upon external inspection, obvious damage to the insulation or housing is visible, further testing may not be necessary - the element requires replacement.
Design and principle of operation of the starting relay
To correctly ring the part, you need to understand its internal structure. In modern refrigerators, two types of relays are most often found: induction (electromagnetic) and posistor. Induction models operate due to electromagnetic force, which, at a certain current, closes the contacts of the starting winding. The posistor uses the property of the semiconductor material (posistor) to sharply increase resistance when heated.
When the refrigerator is turned on, a large current flows through the windings, which causes the posistor to heat up or the electromagnet to operate. As soon as the engine picks up speed, the current drops and the relay opens the starting winding circuit, leaving only the main winding working. If this mechanism is broken, the engine cannot reach operating mode. The circuit also often contains thermal relaywhich opens the circuit when the compressor overheats.
Differences between posistor and electromagnetic relays
Posistor relays have no moving parts and operate silently, changing heating resistance. Electromagnetic ones use a movable core and contacts, which may be accompanied by an audible click each time it starts. PTC resistors are more sensitive to vibrations and shocks during transportation.
Structurally, the device is a plastic case with three contacts for connecting to the compressor and two for connecting to the network (phase and zero). Inside there are copper contacts, springs and the working element itself (posistor or coil). Understanding this circuit is necessary for correctly connecting the multimeter probes during diagnostics.
Necessary tools for testing
For high-quality diagnostics, you will need a basic home repair kit. The main tool will be multimeter (tester). It is advisable to use a digital device, as it allows you to more accurately determine the resistance and continuity of the circuit. Analog dial testers are also applicable, but require reading skills.
In addition to the measuring device, you will need screwdrivers (Phillips and flathead) to remove the protective covers and dismantle the relay itself. In some refrigerator models, access to the compressor may be limited, so a flashlight to illuminate the work area is a good idea. It is also recommended to prepare a soft rag to clean the contacts from dust and possible carbon deposits.
- 🔧 Multimeter with continuity and resistance measurement function.
- 🔧 A set of screwdrivers of different sizes for dismantling.
- 🔧 Flashlight or headlamp for lighting.
- 🔧 Pliers or pliers (careful not to damage the contacts).
- 🔧 Isopropyl alcohol or contact spray for cleaning.
Before starting work, make sure the multimeter is working properly. To do this, switch it to dialing mode and connect the probes to each other - a sound signal should sound. If the device is powered by a battery, check its charge, since a dead battery can give false resistance readings, which will lead to erroneous conclusions about the state of the starting relay.
Step-by-step instructions: how to test the relay with a multimeter
The testing process begins with dismantling. Remove the back cover of the refrigerator, locate the compressor and carefully disconnect the relay box. It is usually secured with a bracket or latches. Disconnect the wires, first remembering or photographing their location so as not to mix up the polarity during assembly. Remove the relay from the housing.
Visually inspect the device. If you hear a ringing sound inside when shaken (like broken glass) or obvious traces of burning are visible, further inspection may not be necessary - the element is faulty. If there are no external defects, we proceed to measurements. Switch the multimeter to resistance measurement mode (Ohm) or continuity testing.
☑️ Algorithm for checking the relay
It is necessary to ring pairs of contacts depending on the type of relay. For posistor models, the resistance between the contacts of the starting winding must be within the normal range (usually 30-60 Ohms, but depends on the model). If the device shows one (infinity) or zero, then the circuit is open or closed. For electromagnetic relays, it is important to check the coil for integrity and mobility of the core.
Pay special attention to the thermal relay if it is built into the housing. Its contacts in a cold state should ring short (resistance close to zero). When heated (which is difficult to check at home without special equipment), they should open. If the circuit does not ring in a cold state, the thermal protection is faulty and requires replacement along with the starting element.
Table of typical values and faults
For ease of diagnosis, below is a table with approximate values and possible causes of deviations. Remember that the exact parameters depend on the compressor manufacturer (Danfoss, Secop, LG, Atlant, etc.).
| Measurement type | Normal reading | Fault reading | Probable cause |
|---|---|---|---|
| Resistance of the posistor | 10 - 50 Ohm | Infinity (1) or 0 | Open circuit or short circuit of the posistor |
| Coil integrity (electromagnetic) | Low resistance | Infinity | Open coil winding |
| Thermal relay contacts | 0 Ohm (ringing) | Infinity | Bimetallic plate burned out |
| Case insulation | Infinity | Any value | Insulation breakdown on the case |
If your measurements coincide with the column “Indication in case of malfunction”, then with a high degree of probability starting relay subject to replacement. However, if the readings are normal and the refrigerator does not start, the problem may lie in the compressor itself (turn-to-turn short circuit of the windings) or in the wiring.
Replacement and precautions
If diagnostics confirm a malfunction, you must purchase a similar part. When choosing, pay attention not only to the refrigerator model, but also to the markings of the compressor itself. Relays from different manufacturers may have similar characteristics, but differ in mounting geometry or contact arrangement.
Installation of a new element is carried out in the reverse order of removal. It is important to ensure a tight fit of the contacts to the compressor terminals. Weak contact will lead to sparking, heating and rapid failure of the new part. After assembly, do not rush to close the back cover - turn on the refrigerator and listen.
⚠️ Attention: Make sure that the relay is installed in the correct position (usually the "UP" arrow should point up). Improper orientation may result in improper operation of the starting mechanism or thermal protection.
Start the unit. The compressor should operate smoothly, without buzzing or frequent clicks. After 10-15 minutes, check whether the condenser (grid at the back) has begun to heat up and whether cold has appeared in the chambers. If the engine hums but does not start, perhaps the problem is not only in the relay, but also in the jamming of the piston group.
When replacing, it is also recommended to check the condition of the wiring going to the compressor. Melted insulation can cause repeated failure. If you are not confident in your abilities or the measurements show complex faults, it is better to contact a professional technician.
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 do this is extremely dangerous and is not recommended. This may lead to burnout of the compressor windings or fire. In addition, without thermal protection, the engine will quickly overheat.
Why does a new relay burn out immediately after installation?
Most often this happens due to a malfunction of the compressor itself (for example, an interturn short circuit that causes an increased starting current) or problems with the voltage in the network. Also, the cause may be incorrect installation or poor contact.
How to distinguish a posistor relay from an electromagnetic one?
Posistor relays are usually smaller in size, do not have moving parts and do not make sounds when shaken. Electromagnetic ones can be larger; inside they have a movable core that can rattle when shaken.
Does room humidity affect the operation of the relay?
High humidity can contribute to oxidation of contacts and a decrease in insulation resistance, which in the long term leads to malfunctions. It is important to ensure good ventilation around the compressor area.