A sudden stop of the compressor or its convulsive attempts to start with a characteristic click often indicates a malfunction of the starter mechanism. It is protective relay responsible for the safe start of the motor and its shutdown during overloads, preventing burnout of the windings. If your refrigerator has stopped freezing, and the motor hums, but does not start, or turns on only for a second, the problem with a high degree of probability lies in this small but critically important unit.
Diagnostics of this element does not require complex professional equipment, but it does require compliance with safety precautions and an understanding of the principles of operation of electric motors. In this article we will look in detail at how to identify a fault visually and using a multimeter, and also consider the nuances of replacing a part. Correct defection will help you save on calling a technician or, at least, accurately understand the cause of the breakdown before purchasing spare parts.
Before starting disassembly, make sure that you have completely de-energized the unit. Working with electrical components of the refrigerator requires caution, since even after disconnection from the network, a residual charge may remain in the capacitors. We will consider testing methods for both common posistor models and older inductive relays found in vintage equipment.
Operating principle and types of start-up protection devices
To understand the diagnostic process, you need to know exactly how this unit functions. Modern refrigerators most often use posistor (solid-state) relays, which replaced bulky induction analogues. A posistor is a semiconductor element whose resistance increases sharply when heated, which allows you to break the starting winding circuit after the engine starts.
Induction devices work differently: they use an electromagnetic coil and a movable core. When current is applied, the core is retracted, closing the contacts of the starting winding, and when the engine speed increases, the current drops, and the core, under the influence of gravity or a spring, opens the circuit. Thermal relay, often combined with the starting winding in one housing, reacts to the current strength: if it exceeds the norm, the bimetallic plate bends and opens the contact, protecting the motor from combustion.
Differences in design directly affect the testing method. PTC resistors have practically no moving parts and fail less often, but they cannot be checked for “sparking” or sticking of contacts as easily as induction ones. Induction ones often suffer from burnt contacts or loss of core mobility. Understanding your unit type is the first step to a successful repair.
⚠️ Warning: Never attempt to test a relay connected to a running compressor without proper skills and insulated test leads. The risk of electric shock at a voltage of 220V is extremely high.
It is important to note that in most modern models, the starting and thermal relays are combined into a single plastic case, which is simply put on the compressor contacts. However, inside these are two independent mechanisms. Thermal protection may work due to overheating, even if the starting circuit is working properly, so during diagnostics you need to check both circuits.
External signs of malfunction and primary diagnostics
Before Instead of picking up a multimeter, it is worth conducting a visual inspection and analysis of the behavior of the refrigerator. Often the symptoms of a breakdown are obvious even to a non-specialist. If you hear a loud click, followed by a hum, and then another click and silence, this is a classic sign that start relay cannot hold or close the contacts to start.
Carefully inspect the plastic housing of the device itself. Look for signs of melting, blackening or soot. If the plastic turns black, it means there has been sparking or overheating inside, which clearly indicates the need for replacement. It is also worth sniffing the element: the smell of burning or melted insulation is a sure indicator of a problem.
- 🔊 The refrigerator makes repeated clicking sounds at intervals of several seconds or minutes.
- 🌡️ The compressor remains cold or barely warm, although it is trying to start.
- ⚡ Kicks out automatic circuit breakers (RCDs) in the electrical panel when trying to turn on.
- 👀 Visual damage to the relay housing or oxidation of the contacts is visible.
Another method of primary testing is acoustic. Gently shake the removed relay near your ear. If something dangles or rattles inside, it means that the mechanical part (core or contacts) is damaged. In a working posistor relay there should be no sounds when shaking, since there is just a ceramic bar and contacts.
⚠️ Attention: If the compressor emits a very loud, low-frequency hum and vibrates strongly when starting, but the relay is working properly, the problem may be in the motor itself (turn-to-turn short circuit). Prolonged attempts to start can permanently destroy the motor.
Do not ignore the condition of the contacts on the compressor itself. Sometimes the reason lies not in the relay, but in oxidized motor pins. If they are blackened or covered with a greenish coating, they must be carefully cleaned before installing a new element. Poor contact causes heating and false protection activations.
Necessary tools and safety measures
For high-quality diagnostics, you will need a minimum set of tools, which most home craftsmen can find. The main device will be multimeter (tester), which allows you to measure resistance and check the integrity of the circuit. Without it, an accurate check of the posistor is almost impossible.
In addition to the measuring device, prepare pliers with insulated handles, a screwdriver (Phillips and flat-head) for removing the compressor casing, and possibly fine sandpaper for cleaning the contacts. It will not be superfluous to have a flashlight on hand, since the space around the compressor is often poorly lit.
☑️ Preparation for diagnostics
Safety is priority number one. Even after unplugging the cord from the outlet, wait 5-10 minutes before starting work. This time is necessary for the compressor to cool down and the capacitors to discharge. Work only with dry hands and shoes with rubber soles to eliminate the risk of electric shock.
If you plan to test the relay under load (which is not recommended for beginners), make sure that all live parts are securely insulated and that you do not touch any metal parts of the refrigerator body. It is best to carry out all resistance measurements with the device completely de-energized and removed from the engine.
When working with the tool, be careful not to damage the copper tubes of the refrigeration circuit. A breakdown of the tube will lead to a freon leak, which will require expensive repairs from specialists with a vacuum decanter and a gas station. Mechanical integrity Cooling systems are more important than electrical diagnostics.
Step-by-step instructions for dismantling the relay
Process Removing the relay is quite simple, but requires care. First, remove the rear protective panel of the refrigerator by unscrewing the mounting screws. A compressor will open in front of you - a black metal “tank”, to the bottom of which a plastic box is attached. This is our desired device.
Carefully remove the retaining clip or bracket that holds the relay to the compressor housing. In some models it is held in place by a tight fit and additional screws. After removing the fixation, smoothly, without sudden jerks, pull the relay down from the compressor pins. It should be removed with little effort.
It is important to remember or photograph which wire fits where. Usually the wires are color coded, but it's better to be on the safe side. Disconnect the wire terminals from the relay itself. If the terminals are oxidized or sit very tightly, use pliers, carefully loosening them from side to side.
After dismantling, inspect the inside of the relay. To do this, you may need to open the plastic case by prying off the latches with a screwdriver. Inside you will see either a ceramic bar (posistor) or a coil with a core (induction). Check for moisture, insects or obvious traces of burning.
If the relay is inductive, check the mobility of the core. It should move freely inside the coil. If it is jammed, the device will not be able to break the starting winding circuit, which will lead to the motor burning out. In such cases, cleaning rarely helps, replacement is required.
Checking with a multimeter: algorithm of actions
The most reliable diagnostic method is checking the resistance with a multimeter. Switch the device to resistance measurement mode (Ohms). First, let's check the thermal protection: ring the contacts that go into the power supply circuit. In a normal (cold) state, the resistance should be close to zero (0.1–0.5 Ohm).
If the multimeter shows infinity (one on the left side of the screen or OL), then the circuit is open. This may mean that the thermal protection has tripped and is not returning, or it has burnt out. Allow the device to cool completely for 15-20 minutes and repeat the measurement. If the result is the same, the relay is faulty.
To check the starting posistor relay, measurements are taken between the contacts to which the starting winding is connected. The resistance of a working posistor at room temperature is usually 15–50 Ohms (the exact value depends on the model). If the resistance is infinitely high or, on the contrary, equal to zero, the element requires replacement.
The induction relay is checked by testing the coil. The winding resistance should be small, but not zero. Also check whether the contacts open when held vertically (for some types) or when the core is heavy. In the “upside down” position, the contacts can be closed, and in the working position they can be open.
Below is a table with approximate resistance values for various types of faults:
| Test type | Normal value | Symptom malfunction | Action |
|---|---|---|---|
| Thermal protection (cold) | 0.1 - 1.0 Ohm | Infinity (∞) | Replacement relay |
| Posistor (starting) | 15 - 50 Ohm | 0 Ohm or ∞ | Replacement of the posistor/relay |
| Induction coil | 10 - 30 Ohm | ∞ (break) | Replacement of relay |
| Contacts (short circuit) | 0 Ohm | High resistance | Cleaning or replacement |
⚠️ Attention: Multimeter readings may vary slightly depending on the ambient temperature. PTC resistors are sensitive to heat: immediately after operation their resistance will be high.
If all checks showed normal, but the refrigerator does not work, the problem may be in the compressor itself. Try (for a short time!) supplying power directly, bypassing the relay, but only if you are confident in your abilities. If the motor hums and does not start even with a direct connection, the compressor is most likely jammed.
Replacement of the protective relay and final assembly
If the diagnostics confirmed the malfunction, you need to purchase an analogue. The ideal option is to find a relay with the exact same model number indicated on the housing. However, you can often use universal analogues if the electrical characteristics match: engine power, type of refrigerant and voltage.
Installation of a new device is carried out in the reverse order of removal. Push the relay onto the compressor pins as far as it will go. Make sure it fits snugly and doesn't wobble. Attach the retaining bracket or clamp. Connect the wires according to the previous photographs or color markings.
Is it possible to use a relay from another refrigerator model?
Using a relay from another model is possible if the basic parameters match: coil voltage, cut-off current and overall dimensions. However, it is better not to experiment, since an incorrect cut-off current can lead to the compressor burning out or the inability to start.
After assembly, do not rush to close the back panel. Plug in the refrigerator and listen. Startup should be smooth, without loud clicks or buzzing. The compressor should pick up speed and run smoothly. If after 10-15 minutes of operation the relay body does not heat up to a burning state, it means that the installation was successful.
Check the operation of the refrigerator within a few hours. Make sure it reaches the temperature and turns off when it reaches the set parameters. If the operating cycle is normal, you can replace the protective panel and tighten the screws.
In conclusion, it is worth noting that regular maintenance, such as cleaning the condenser from dust and providing ventilation, reduces the load on the compressor and prolongs the life of the start-up valves. Taking care of equipment is the best guarantee of its longevity.
Frequently asked questions (FAQ)
Is it possible to repair a burnt-out relay or just replace it?
In 95% of cases, the relay must only be replaced. PTC resistors cannot be restored, and contacts in inductive relays often burn out completely. An attempt to clean the contacts gives only a temporary effect, after which the problem returns after a few days or weeks.
Why does a new relay burn out immediately after installation?
This is a sure sign that the compressor itself is faulty (turn-to-turn short circuit of the windings or mechanical wedge). The reason may also be incorrect selection of relays for current or voltage. In such cases, diagnostics of the motor-compressor is required.
How much does a start-up relay cost and is it difficult to find?
The cost varies from 300 to 1500 rubles, depending on the model and manufacturer. You can find them in appliance parts stores or order them online using your refrigerator model number. Universal relays are cheaper, but require precise selection of parameters.
Is it dangerous to operate a refrigerator with a faulty relay?
Yes, it is dangerous. If the relay does not open the circuit when overloaded, the compressor may overheat and burn out, resulting in costly repairs. In addition, constant attempts to start create a load on the wiring, which can cause a fire.
Is it necessary to evacuate freon to replace the relay?
No, it is not necessary. The start-up relay is located on the electrical part of the compressor and is not connected to the refrigeration circuit. Replacement is carried out without violating the tightness of the system and without loss of refrigerant.