A sudden stop of the compressor or its hum without starting is always a signal that a failure has occurred in the cooling system. Most often, the problem lies not in the motor itself, but in a small element that controls its start. A start-up protection relay is a compact device responsible for supplying voltage to the motor windings and protecting it from overloads. If this component fails, the refrigerator stops cooling and food begins to spoil.
Diagnostics of this part does not require sophisticated equipment, but requires compliance with safety measures and care. You will need a minimum set of tools and a basic understanding of electrical circuits. In this article, we will look at how to identify a malfunction visually, take measurements with a multimeter and determine whether the element can be restored or requires replacement.
Before proceeding with disassembly, it is important to understand that starting relay and thermal relay are often combined into one housing. It is this block that we will check. Errors in diagnostics can lead to the purchase of unnecessary spare parts or, worse, to the failure of an expensive compressor. Therefore, each step must be performed sequentially, excluding other possible causes of failure.
⚠️ Attention: Carry out all work on checking the electrical components of the refrigerator only after completely disconnecting the device from the power supply. Residual voltage in the capacitors can be dangerous; let the equipment stand turned off for 10–15 minutes before starting work.
Main signs of a faulty start relay
The first step in diagnosis is to observe the behavior of the refrigerator. A faulty relay often manifests itself with characteristic audible and visual signals. If you hear a clicking sound, followed by a humming sound from the motor, and a few seconds later another clicking sound followed by silence, this is a classic symptom. The compressor tries to start, but cannot turn the shaft, and the thermal protection is triggered.
Sometimes the situation looks different: the motor hums constantly, but the refrigerator does not freeze. In this case, the relay may become stuck and continue to supply current to the starting winding, causing excessive heat and a risk of fire. It is also worth paying attention to the smell of burning or melted plastic in the compressor area, which indicates overheating of the contacts.
The main symptoms that require checking include:
- 🔊 The compressor makes a loud click, hums for 3-5 seconds and turns off.
- 🔥 Relay housing or the compressor gets very hot during operation.
- 🧊 The refrigerator has stopped freezing, although the light inside is on.
- ⚡ The circuit breaker (RCD) in the apartment is knocked out when the refrigerator is turned on.
It is important to distinguish between a relay failure and a malfunction of the compressor itself. If the motor hums but does not start, the problem may be a jammed piston group or broken windings. However, in most cases (about 80%) the culprit is trigger mechanism. If the compressor is silent and does not make any sounds when plugged in, the problem may be in the thermostat or wiring.
Visual inspection and initial diagnostics
Before picking up a multimeter, it is necessary to conduct a thorough visual inspection of the removed relay. Often external signs say more about the problem than complex measurements. Remove the back cover of the refrigerator, disconnect the wires and carefully remove the relay from the compressor tail. Pay attention to the condition of the case: the presence of cracks, traces of soot or melted plastic indicates a short circuit or overheating.
If the relay case is transparent or translucent, inspect the insides. There should be no black deposits inside, and the contacts should be clean. Darkening of the inner walls or the presence of a burning smell is a sure sign that the device is faulty. Also check the condition of the contacts on the compressor itself: they should be dry and clean.
Pay special attention to the type of your relay. There are induction (electromagnetic) and posistor models. Induction relays have a movable core and contacts that can burn. Posistor contain a ceramic element (posistor), which changes resistance when heated. Visually, a posistor often looks like a tablet or disk inside a housing. If it is crumbled or blackened, it must be replaced.
There are situations when the relay looks perfect in appearance, but does not work. An internal coil break or loss of magnetic properties of the core is not always visible to the eye. Therefore, a visual inspection is only the first stage, which must be followed by an instrumental check.
Instrumental testing with a multimeter
For accurate diagnostics, you will need a multimeter (tester). Switch the device to resistance measurement mode (Ohms). If you have an induction relay, place it so that the core can move freely under the influence of gravity. In a vertical position (as on a compressor), the contacts should be open and the device should show infinity.
Turn the relay 180 degrees. In this position, the core should lower and close the contacts. The multimeter should show resistance close to zero. If the contacts do not close when turned over or, conversely, are closed in any position, the relay is faulty. Also check the coil: the winding resistance should be within normal limits (usually from 10 to 100 Ohms, depending on the model), but not infinite.
For posistor relays, the procedure is slightly different. There are no moving mechanical parts. You need to measure the resistance between the contacts to which the compressor starting winding is connected. It should be several ohms (usually from 3 to 50 ohms). If the device shows one (infinity) or zero, the posistor is broken or broken.
Do not forget to check the thermal protection, if it is built into the housing or is a separate element. Ring the thermal relay circuit: in a cold state it should ring (show zero). If the resistance is infinitely high, it means that the bimetallic plate has already worked or is broken, and the current does not pass.
☑️ Test algorithm with a multimeter
Checking the relay without a multimeter
There are situations when there is no tester at hand, and The refrigerator needs to be checked urgently. There is a method of direct voltage application, but it requires extreme caution and understanding of the risks. This method allows you to determine whether the compressor is able to start without the participation of a relay. The essence of the method is to apply voltage directly to the working and starting windings.
This will require a piece of wire with a plug. One end is connected to the common terminal of the compressor, the other to the working winding. A wire is connected to the starting winding, which briefly (for 1–2 seconds) closes with the wire from the network. If the compressor starts and runs, then the problem is in the relay. If it hums and does not start, the problem is in the motor.
Important: this method is dangerous and is not recommended for beginners. Incorrect connection may result in electric shock or damage to the windings. In addition, starting without protection can be dangerous if there is an interturn short circuit in the system.
A safer, but less accurate method is the exclusion method. If you have a known good relay from another refrigerator (of the same power and type), you can install it for testing. If the refrigerator works with the new relay, it means the old one is faulty. However, this method requires the availability of a spare part.
⚠️ Attention: Direct voltage supply to the compressor windings should only be carried out by qualified personnel. Prolonged supply of current to the starting winding without shutting off will lead to its combustion in a matter of seconds.
Table of typical faults and solutions
To organize data and quickly make decisions, it is convenient to use a pivot table. It will help compare the measurement results with possible causes of failure. Please note that resistance values may vary slightly depending on the compressor manufacturer (Danfoss, Secop, Atlant).
| Symptom | Connection result | Probable cause | Solution |
|---|---|---|---|
| Clicks, but does not start | Contacts do not close when turned over | Contacts sticking or worn out | Replacing the relay |
| Buzzes and turns off | The coil resistance is infinite | Breakage of the coil winding | Replacing the relay |
| Does not turn on at all | Thermal relay does not ring | Tripped thermal protection | Cool and check, replace if repeated |
| Humming, burning smell | The posistor resistance is 0 or ∞ | Thermal breakdown | Replacing a posistor or the entire relay |
If the diagnostics showed that the relay is working, but the refrigerator does not work, the problem may lie deeper. The compressor itself, the thermostat or the control unit (in models with No Frost) may be faulty. In such cases, it is better to contact professionals, since further repairs require special tools and knowledge.
Why does the new relay burn out?
A frequent reason for the new relay to burn out again is a malfunction of the compressor itself. If the motor is “heavy” or has an interturn short circuit, the starting currents exceed the norm, and the contacts of the new relay quickly burn out. Also, the reason may be low voltage in the network.
Replacement of the relay and commissioning
After you are convinced that the old part is faulty, you need to purchase an analogue. It is critically important to select a relay with identical characteristics: motor power (in watts or horsepower), type of compressor and direction of the rod (vertical or horizontal). The part number indicated on the case will help you find an exact replacement in spare parts catalogues.
The replacement process is simple: remove the old relay by disconnecting the wires (after photographing the circuit). Install the new device onto the three pins of the compressor. It should fit tightly, without play. Connect the wires according to the diagram or color coding you made earlier. Typically, the red wire goes to the starting winding, white or black to thermal protection, and yellow-green to grounding.
After assembly, plug in the refrigerator. The first few minutes of operation should pass without any extraneous sounds. The compressor should start with a characteristic hum, after a few seconds the hum may change slightly (the starting winding will turn off), and the unit will go into operating mode. Check if the evaporator begins to freeze.
If after replacing the relay the situation has not changed, perhaps the problem was not in it, or the new component was also defective. In rare cases, it is necessary to immediately replace both the relay, the thermal protection, and even the capacitor, if it is present in the circuit.
Is it possible to repair a burnt-out relay yourself?
Theoretically, an induction relay can be disassembled, clean the contacts with fine sandpaper and put back together. However, this is a temporary measure. The factory silver plating of the contacts is broken, and after a short time they will burn again. PTC relays cannot be repaired because they are monolithic. Experts recommend not to take risks and install a new part, the cost of which is low.
Why does the relay heat up during operation?
Slight heating of the relay body is a normal phenomenon, especially for induction models, where current passes through the coil. However, if the housing becomes so hot that it is impossible to touch it, or there is a smell of burning insulation, this is a sign of a malfunction. Perhaps the relay does not turn off the starting winding, which leads to an overload.
How often do you need to change the refrigerator relay?
The relay is a resource part, but its service life usually coincides with the service life of the compressor (10–15 years). Unscheduled replacement is required only when it fails. Frequent power surges in the network can shorten the service life of the element, so it is recommended to connect the refrigerator through a surge protector or stabilizer.
What is the difference between the relays for Atlant and Indesit?
The difference lies in the mounting design, contact location and electrical characteristics. Relays from Atlant often have vertical mounting and a specific housing shape, while for Indesit (often using Danfoss/Secop compressors) horizontal models are typical. Installing an unsuitable relay can lead to the fact that it simply will not fit on the bayonets or will not work correctly.
Is it dangerous to operate a refrigerator with a faulty relay?
Yes, it is dangerous. If the relay “sticks” and does not turn off the starting winding, the compressor will quickly overheat, which can lead to a fire. If the relay does not start the motor and the refrigerator continues to hum, this also creates a risk of a wiring fire. At the first sign of a malfunction, operation should be stopped.