A sudden stop of the compressor or characteristic clicks when trying to start the refrigerator often indicate a failure of the start relay. This small but critical element is responsible for supplying voltage to the motor windings at the moment of start. If starting relay faulty, the motor hums, but does not start, or turns on only for a few seconds, after which the thermal protection is activated.
Restoring the unit's functionality in such a situation does not always require calling a technician. In many cases, replacement or relay repair is accessible even to a non-professional with basic tools and an understanding of how the device operates. However, it is important to accurately diagnose the problem, since the symptoms may be similar to a breakdown of the compressor or thermostat itself.
In this article we will analyze in detail the device of the starting relay, methods for diagnosing it with a multimeter and a step-by-step replacement algorithm. You will learn how to distinguish a burnt winding from stuck contacts and what to look for when buying a new part for your Indesit, Atlant or Beko.
⚠️ Attention: Before starting any work on repairing a refrigerator, be sure to disconnect the device from the power supply. Working with electrical appliances under voltage is dangerous to life and can lead to a short circuit.
Design and principle of operation of the starting relay
The starting relay is an electromechanical switch that closes the circuit of the engine starting winding only at the moment of starting. As soon as the compressor rotor reaches the required speed, the relay opens the contacts and the engine continues to operate on the main winding. There are two main types of such devices: induction (with a coil and a moving core) and posistor (thermal).
Induction models, which are often found in old Soviet refrigerators and units Zil, use an electromagnetic coil. When current is applied, the core retracts and closes the contacts of the starting winding. When the current drops after starting, the core, under the influence of gravity or a spring, returns to its original position, breaking the circuit. In modern models, such as LG or Samsung, posistors are more often used.
The posistor relay works on the principle of changing the resistance of a ceramic element when heated. When cold, the resistance is low and current flows freely through the starting winding. The passing current heats up the posistor, its resistance increases sharply, and the circuit actually breaks. This process takes only a few seconds. Failure of the posistor often manifests itself in the fact that it does not cool down or has cracks.
What is the difference between the top and side connections?
The difference lies in the orientation of the contacts and the method of attachment to the compressor. Side connection relays (contacts on the side) are often labeled PTC and are used in refrigerators with a horizontal compressor, while top connection is typical for vertical models. It is important to select relays strictly according to the catalog number or connection type, since they may not physically fit the compressor pins.
Fault symptoms and initial diagnostics
You can determine that the problem lies in the relay by a number of characteristic signs. The most obvious symptom is that the refrigerator does not turn on, only a quiet hum or click is heard, after which there is silence. After some time, the cycle may repeat. This indicates that the compressor is trying to start, but starting winding does not receive a pulse or the circuit is immediately broken.
Another sign is overheating of the compressor. If the motor hums but does not start, it quickly heats up and the thermal protection relay is triggered, turning off the unit completely. In some cases, you may hear a burning smell or see sparking in the compressor area if the relay is stuck in the closed state. Also, the refrigerator may work, but not gain temperature, if the relay “sticks” and does not allow the motor to enter operating mode.
For an initial check, you can gently tap the relay body (with the refrigerator turned on but not working, being careful). If the compressor starts after a slight blow, it means that the relay mechanism is stuck or the contacts have oxidized. However, this is a temporary solution, and it is better not to postpone replacement, since operating the engine in this mode leads to rapid wear.
Removing the relay and visual inspection
To get to the relay, you need to remove the rear protective panel of the refrigerator. It is usually secured with screws or snaps. After removing the cover, you will see the compressor (black tank), which is connected to copper pipes and an electrical cable. The relay is mounted directly on the side or top of the compressor and is covered with a plastic casing.
The dismantling process requires care. First, disconnect the connector with the wires coming from the network. Next, remove the retaining bracket or bar that holds the relay to the compressor pins. It is important not to use excessive force to avoid damaging the ceramic pin insulators. After removing the lock, the relay is easily removed from the contacts.
- 🔍 Carefully inspect the relay body for melting, cracks or traces of burning.
- 🔍 Shake the relay next to your ear: if you hear a rattling sound, it means that a piece of the mechanism or core has broken off inside.
- 🔍 Check the condition of the contacts: they must be clean, without oxidation and soot.
- 🔍 Pay attention to the internal cavity: the presence of black soot or a burning smell indicates a short circuit.
If visual inspection reveals obvious damage, such as a destroyed posistor housing or burnt wires, Further diagnostics may not be required - the part requires replacement. However, to be completely sure, it is recommended to carry out electrical measurements.
☑️ Checklist before removing the relay
Checking the relay with a multimeter
The most accurate diagnostic method is to check the continuity of the circuit and resistance using a multimeter. To do this, switch the device to resistance measurement mode (Ohm). If you have an induction relay, check the coil resistance: it should be within the normal range (usually from 30 to 100 ohms, depending on the model). Infinite resistance will indicate a winding break.
For posistor relays, testing is carried out by measuring the resistance between the contacts. In a cold state, the resistance of the posistor should be low (several tens of ohms). If the multimeter shows one (infinity) or zero, then the posistor is faulty. It is also important to check the thermal protection relay, which is often built into the same housing as the starting one.
| Relay type | Normal resistance | Fault symptom | Action |
|---|---|---|---|
| Induction | 30–100 Ohm (coil) | Infinity or 0 Ohm | Replacement relay |
| Posistor | 10–50 Ohm (cold) | Infinity in a cold state | Replacing a posistor/relay |
| Thermal | 0 Ohm (closed) | Infinity (break) | Replacing the thermocouple |
| Contact | 0 Ohm (when shorted) | Resistance or sparking | Cleaning or replacement |
When checking, the thermal relay (bimetallic plate) should “ring” short. If the circuit is broken at room temperature, it means that the protection worked earlier and did not return to its original state, or burned out. Warming up with a hairdryer can temporarily restore contact, but it is better to replace such a part.
⚠️ Attention: If after checking it turns out that the relay is working, but the compressor still does not start, the problem may be in the engine itself (turn-to-turn short circuit) or in the wiring. Do not try to “start” the compressor directly without a relay - this is guaranteed to lead to burnout of the winding.
Selecting an analogue and replacing the relay
Finding an original relay for older refrigerator models can be difficult, but fortunately, most starters are universal. The main thing when selecting is the correspondence of the compressor power (indicated on the nameplate, for example, 1/5 HP, 1/4 HP) and the type of connection (top or side). It is also important to consider the diameter and location of the pins.
Replacement is carried out in the reverse order of removal. Install the new relay onto the compressor pins as far as it will go. Make sure it fits snugly and doesn't wobble. Attach the retaining bar or bracket. Connect the wires to the relay contacts: they are usually color-coded or labeled (L, N, S, R), but it is better to take a photo of the circuit before disassembling.
After assembly, do not rush to close the back panel. Plug in the refrigerator and listen. The startup should be quiet, without loud clicks or buzzing. The compressor should pick up speed and run smoothly. If after 10-15 minutes it heats up and turns off, it means that the problem has not been resolved or the wrong relay has been selected.
Common mistakes during repairs
One of the most common mistakes is neglecting to clean the contacts. Even a new relay can become unstable if the contacts on the compressor itself are oxidized. It is recommended to carefully clean the compressor pins with fine sandpaper before installing a new part.
Another error is incorrect orientation of the relay. Many models are designed to work only in a certain position (for example, up arrow). If you install the relay upside down, gravity will prevent the core from falling down and breaking the circuit, which will burn out the starting winding. Always follow the marking UP or arrows on the case.
- 🚫 Trying to repair a burnt posistor by gluing or soldering is useless, the material changes properties irreversibly.
- 🚫 Using a relay with an inappropriate cut-off current, which leads to constant false shutdowns.
- 🚫 Ignoring checking the voltage in the network: low voltage can also prevent the compressor from starting.
Also, do not forget about the capacitor if it is present in the circuit (usually in powerful models). If the capacitor is swollen or has lost capacity, the relay will operate in extreme mode and quickly fail. Checking the capacitor should be part of a comprehensive diagnosis.
Is it possible to repair the relay rather than change it?
Theoretically, in induction relays you can clean the contacts or bend the spring, but this is a temporary measure. In posistor relays, replacing the ceramic element is possible, but it is labor-intensive and requires soldering. Considering the low cost of a new relay, repairing the old one is most often impractical and less reliable.
Why does a new relay burn out immediately after installation?
This may indicate a malfunction of the compressor itself (jamming, interturn short circuit) or problems with the power supply (voltage surges). It is also possible that a relay with incorrect cut-off current characteristics was selected.
How to determine the compressor power to select a relay?
The power is indicated on the sticker on the compressor body (for example, 1/5 HP, 1/4 HP, 1/3 HP). You can also focus on the refrigerator model and find technical specifications in the documentation or on specialized forums.
What is the difference between the RT and R-1 relays?
These are the markings of Soviet and post-Soviet relays. RT (thermal) and R-1 (launch) are often paired or combined. They differ in operating currents and dimensions. It is important to select an analogue that matches the original in terms of cut-off current.
The compressor hums after replacing the relay, what should you do?
If the humming changes to quiet operation, this is normal. If the loud hum remains and the refrigerator does not cool, the relay may not fit (does not open the circuit) or there is a problem in the mechanical part of the compressor. Check whether the starting winding circuit opens after starting.