A sudden stop of the compressor is always stressful for the owner of household appliances, because this entails the risk of product damage and the need for urgent repairs. Often the reason lies not in the motor itself, but in a small but critical element of the circuit - the starting relay, which is responsible for starting the engine and protecting it from overloads. Understanding how to check the refrigerator switch-on relay can save you a significant amount of money on calling a technician and extend the life of the unit.
This component supplies voltage to the electric motor windings at the right time, and also opens the circuit when the required rotor speed is reached. If this mechanism fails, the compressor either hums but does not start, or turns on for a few seconds and immediately turns off. Diagnostics begins with a visual inspection and listening to the sounds that the unit makes when trying to start.
In this guide we will examine in detail the device of the starting relay, its symptoms faults and step-by-step testing algorithm using a multimeter. You will learn how to safely remove the part, what parameters to pay attention to, and whether you can replace it yourself. Proper implementation of these manipulations will allow you to accurately determine the culprit of the breakdown.
The operating principle and design of the starting relay
To effectively carry out diagnostics, you need to understand exactly how this unit is designed. The start relay is an electromagnetic switch that responds to the amount of current flowing through the compressor windings. When the refrigerator is turned on, the current is high, which causes the contacts to close and voltage to the starting winding of the motor.
As soon as the rotor picks up speed, the current drops, the electromagnet weakens, and the contacts open, turning off the starting winding. In parallel with this, a thermal relay often operates, which opens the circuit completely when the motor overheats or jams. In modern models, these functions can be combined in one housing PTC relay, where the role of a switch is performed by a ceramic element with a positive temperature coefficient of resistance.
The design can be induction (with a coil and a moving core) or posistor. Induction relays are more often found in older models of refrigerators Atlant or Biryusa, while posistor relays are widely used in technology Indesit, LG and Samsung. Understanding the type of your relay is important, since the methods for their initial testing may differ slightly.
Main signs of a relay malfunction
You can determine that the problem lies in the trigger mechanism by the characteristic signs that appear in the operation of the refrigerator. Most often, owners are faced with a situation where the engine tries to start, makes a loud click or hum, but turns off after a few seconds. This is a classic symptom that the starting winding circuit does not open or close in time.
Another clear sign is the complete failure of the compressor to start when the backlight is working and the thermostat is working. In some cases, the relay may “stick” in the closed state, which leads to continuous operation of the engine without stopping, which is fraught with overheating and burnout of the windings. It is also worth paying attention to the smell of burning or the melted body of the part itself.
- 🔊 The compressor hums for 5-10 seconds, then a click is heard and it goes silent.
- 🔊 The refrigerator turns on and off every 20-40 seconds (cyclic operation).
- 🔊 You can hear a crackling or sparking sound in the compressor area when starting.
- 🔊 The engine does not respond to the thermostat turning on, although there is voltage in the network.
If you observe such symptoms, the probability of a relay malfunction is more than 60%. However, before dismantling, it is necessary to exclude problems with the electrical wiring and the compressor itself. Thermal protection can also give similar symptoms if it operates falsely due to wear.
Preparation for diagnostics and safety measures
Before you begin Before checking, it is necessary to ensure the safety of the work, since you will be dealing with electric current and mechanical components. The first and most important step is to completely disconnect the refrigerator from the power supply. It is not enough just to turn off the button, you need to unplug the plug from the socket.
Then you need to gain access to the compressor, which is usually located in a niche at the bottom rear of the unit. You will need to remove the protective cover, which may be secured with latches or screws. In some models, for example, in old ZIL or Minsk, access may be limited by the design of the case, and you will need to remove the back wall completely.
⚠️ Attention: Before touching any contacts, make sure that the capacitors (if they are in the circuit) are discharged, although they are rare in domestic refrigerators. Work only with dry hands and use tools with insulated handles.
To carry out high-quality diagnostics, you will need a multimeter (tester), a screwdriver, pliers and, possibly, a contact cleaner. It is also recommended to take a photograph of the wire connection diagram before disconnecting them, so as not to mix up the contacts during assembly. This is especially true for relays with a large number of pins.
☑️ Preparation for checking the relay
Dismantling and visual inspection of the part
After removing the protective cover, you will see the compressor to which the wiring harness fits. The starting relay is usually placed directly on the terminals of the motor windings and secured with a bracket or simply sits tightly on the contacts. Carefully remove the retaining bracket and disconnect the connector with the power wires.
Remove the relay from the compressor pins. Proceed with caution, as the plastic housings of older parts may be brittle and crumble over time. If the relay is a posistor, it can be mounted on the frame together with the capacitor; in this case, unscrew the mounting screws.
The first stage of testing is a thorough visual inspection. Look for signs of soot, melted plastic, blackened contacts, or swelling of the case. If you can hear the sound of dangling parts inside the relay when shaking, this is a sure sign of destruction of the internal mechanisms or coil.
What do the colors of the wires mean?
Usually the black wire is the phase (power), red or white goes to the starting winding, and blue or yellow-green is ground or zero. However, color markings may vary between manufacturers, so a photograph before disassembly is critical.
If no external defects are found, this does not guarantee serviceability, since an open circuit or breakdown of the posistron is not visually visible. The internal contacts could be oxidized or coated with carbon deposits, which requires disassembling the relay housing, if it allows this to be done without destruction. In the case of non-separable models Danfoss or analogues, visual inspection is limited to the external condition.
Checking a relay with a multimeter: step-by-step instructions
The most accurate diagnostic method is to test the circuit using a multimeter. Switch the device to resistance measurement mode (Ohm) or continuity mode. If you have an induction relay, first determine the location of the contacts: power input, output to the starting winding and output to the main winding.
When ringing in the normal position (horizontally, as it was on the compressor), the circuit between the input and the contact of the main winding should ring (show zero or close to zero resistance). The starting winding circuit must be open. If you flip the relay (simulating a start), the contacts of the starting circuit should close.
For posistor relays, the procedure is simpler: the resistance between the contacts is measured. It should be within a few tens of ohms (usually from 15 to 50 ohms). If the device shows one (infinity) or zero, the element is faulty. It is also important to check the thermal relay, which is often built into the overall design.
| Test type | Normal reading | Fault | Probable cause |
|---|---|---|---|
| Resistance posistor | 15 - 50 Ohm | 0 Ohm or ∞ (infinity) | Short circuit or open circuit |
| Induction relay contacts | Closed when tilted | Does not close or sticks | Pollution, carbon deposits, mechanical jamming |
| Thermal protection | Closed (0 Ohm) | Open (∞) | Bimetallic plate combustion |
| Case insulation | ∞ (infinity) | Yes conductivity | Insulation breakdown, life-threatening |
Alternative testing methods and nuances
In situations where I don’t have a multimeter at hand; you can use the direct voltage supply method, but it requires extreme caution and experience. The essence of the method is to supply 220V directly to the compressor windings, bypassing the relay. If the motor starts and runs smoothly, then the problem is definitely in the relay.
This method is dangerous, since the compressor is left without thermal protection. You can keep it turned on in this mode for no more than 5-10 seconds. There is also a method of checking “by ear”: if, when you turn on the refrigerator, the relay makes a quiet click, but the compressor does not start, the contacts may have stuck or the posistron has burned out.
It is worth considering that some modern inverter compressors do not have a classic starting relay in the usual sense. Their launch is controlled by an electronic module. An attempt to check or replace the “relay” in an inverter refrigerator Electrolux or Bosch without knowledge of electronics can lead to failure of an expensive inverter.
⚠️ Attention: Never leave the compressor plugged in without a working thermal relay for more than 10 seconds. This can lead to overheating and engine wedge, after which repairs will become economically unfeasible.
If after replacing the relay the refrigerator started working, but after a while it stopped turning on again, the problem may be deeper. Perhaps the compressor has exhausted its service life, has an interturn short circuit or low compression. In such cases, simply replacing the starting group will not help.
Replacement and selection of a new relay
If diagnostics confirm a malfunction, the relay must be replaced. The selection of a new part is carried out strictly according to the markings of the old one or according to the model of the refrigerator. It is important to pay attention to the compressor power (indicated on the nameplate, for example, 1/4 hp or 1/3 hp) and the type of refrigerant, since the current characteristics of the relay depend on this.
Universal relays often have an adjusting screw for setting the shutdown current, but it is better to use original spare parts or high-quality analogues from well-known manufacturers, such as Danfoss, Seco or Indesit. Installation is carried out in the reverse order: first we put it on the contacts of the compressor, then we connect the wires.
After assembly, turn on the refrigerator and listen. The launch should be confident, without prolonged buzzing. After 10-15 minutes of operation, check the temperature of the evaporator - it should begin to decrease. If the compressor operates quietly and evenly, the repair can be considered successful.
Can an old relay be repaired?
An induction relay can sometimes be revived by cleaning the contacts with fine sandpaper or a file if they are burnt. PTC relays cannot be repaired and must be replaced entirely.
Frequently asked questions (FAQ)
How much does a starting relay for a refrigerator cost?
The cost depends on the model and manufacturer. For domestic refrigerators, the price can range from 300 to 600 rubles. For imported models (LG, Samsung, Bosch), the price of the original part varies from 800 to 2000 rubles. Universal analogues are cheaper, but may require adjustment.
Can a relay burn out due to a power surge?
Yes, this is one of the common causes of failure. Voltage surges in the network can lead to breakdown of the posistor insulation or burning of the induction relay contacts. To protect equipment, it is recommended to use voltage stabilizers or surge protectors.
Why does the new relay not start the compressor?
There may be several reasons: the relay power is incorrectly selected, the compressor itself is faulty (jammed or shorted windings), or a problem in the wiring/thermostat. It is also possible that the new relay is defective, which occurs when buying cheap analogues.
How often do you need to change the starting relay?
The starting relay is a resource part, but it does not require scheduled replacement. It lasts until it breaks down, which usually happens after 5-10 years of operation. If the refrigerator works stably, there is no need to change the relay “just in case.”