Failure of the start relay is one of the most common reasons why the refrigerator stops cooling, although the light inside is on. Owners of household appliances often encounter a situation where compressor the engine hums for a few seconds, then a click is heard and the engine goes silent. This is a classic symptom that the trigger mechanism cannot start the motor rotor, and the thermal protection is triggered.
Independent replacement of this part does not require deep knowledge in electrical engineering, but requires strict adherence to safety precautions. Before you begin, you need to understand that inside the compressor housing there is refrigerant under pressure, and the terminals are under high voltage. Start relay This is a relatively inexpensive component that can be replaced yourself if you act carefully and consistently.
In this article we will analyze the start relay device, diagnostic methods and detailed algorithm of actions for its replacement. You will learn how to correctly determine the polarity of the windings, check the integrity of the contacts and avoid mistakes when installing a new part. A competent approach will extend the life of your refrigerator without calling a technician.
⚠️ Attention: Before starting any work on repairing the refrigerator, be sure to disconnect the appliance from the electrical network. Working with electrical appliances under voltage is deadly.
Operating principle and design of the starting relay
The starting relay is an electromechanical switch that supplies voltage to the starting winding of the engine only at the moment of starting. As soon as the compressor rotor reaches the required speed, the relay opens the starting winding circuit, and the engine continues to operate on the main working winding. There are two main types of such devices: induction (with a coil) and posistor (thermal).
Induction relays operate due to electromagnetic induction. The current passing through the working winding creates a magnetic field that draws in the core and closes the contacts of the starting circuit. Posistor models use the property of semiconductor material to sharply increase resistance when heated. When current is supplied, the posistor heats up, its resistance increases, and the current through the starting winding practically stops.
Visually, the relay is a plastic case that is placed directly on the terminals of the compressor. Inside there are contacts, springs and, depending on the type, a coil or a posistor element. Thermal protection relay, which is often combined with the starting unit into one unit, monitors the temperature of the motor and opens the circuit when overheated.
- 🔌 Contact group: provides switching of power circuits windings.
- 🧲 Electromagnetic coil: creates a field for closing contacts (in induction relays).
- 🔥 Posistor: a ceramic element that changes resistance when heated.
- 🛡️ Bimetal plate: element of thermal protection against overloads.
⚠️ Attention: Do not try to repair the inside of the relay (glue contacts, clean the posistor). This unit is considered disposable and can only be completely replaced if it malfunctions.
Diagnostics of faults before replacement
Before buying a new part, you need to make sure that the problem lies in the relay, and not in the compressor or wiring itself. Primary diagnosis is carried out visually and auditorily. If, when you turn on the refrigerator, you hear a loud click, followed by the hum of the motor, lasting 3-5 seconds, and again a click with attenuation, this is a sign of a malfunction of the starting mechanism or jamming of the compressor.
For a more accurate check of the relay, it is necessary to remove it from the compressor. Remove the rear protective cover of the refrigerator, locate the compressor and carefully remove the plastic casing covering the contacts. Disconnect the wires going to the relay and remove the part itself. Carefully inspect the case for melting, cracks or traces of burning.
If there is no external damage, you can check with a multimeter. In posistor relays, the resistance between the contacts in a cold state should be in the range of 20-60 Ohms. If the device shows an open circuit or resistance close to zero (short circuit), the part is faulty. You should also check thermal relay: in a cold state it should “ring” (have zero resistance), and when heated, open the circuit.
Necessary tools and preparation for work
Replacing the starting relay - a procedure not requiring complex specialized equipment. However, to perform the work efficiently and ensure safety, it is necessary to prepare a set of basic tools. The absence of the necessary tool can lead to damaged terminals or poor contact, which will cause repeated failure.
First of all, you will need a set of screwdrivers (Phillips and flathead) to remove the protective panels and clamps. To work with electrical contacts and check the circuit, you need multimeter (tester). You may also need needle nose pliers and electrical tape or heat shrink to insulate the connections.
An important step in preparation is finding the right replacement part. Relays are selected strictly according to the compressor model or the catalog number of the old device. There are no universal solutions, since the mounting geometry and electrical characteristics from different manufacturers (Danfoss, Atlant, Indesit) may differ.
☑️ Tools for replacing relays
⚠️ Attention: If a green coating is visible on the compressor contacts (oxidation), be sure to sand them down with fine sandpaper before installing the new relay. Poor contact will lead to heating and melting of the plastic.
Connection diagram and terminal marking
The most critical point in the replacement process is the correct connection of the relay to the compressor terminals. An error in the connection can lead to burnout of the motor windings or failure of a new part. On the housing of most modern compressors, the terminals are marked with letter designations that comply with international standards.
Usually, three main terminals can be seen on the terminal strip. The symbol C (or R in some schemes) indicates a common point (Common). Output R (Run) is intended for the working winding, and output S (Start) is for the starting winding. The starting relay is placed on the terminals of the starting and working windings, and the thermal relay is often connected to the common terminal and the working one.
If the markings are erased or missing, you can determine the windings using a multimeter in resistance measurement mode. The resistance between the common point and the working winding is always less than that between the common point and the starting winding. The resistance between the starting and working windings will be equal to the sum of the two previous values.
| Marking | Purpose | Wire color (typical) | Resistance |
|---|---|---|---|
C (Common) |
General output | Black / Red | Basic reference point |
R (Run) |
Working winding | Blue / White | Low (10-30 Ohm) |
S (Start) |
Start winding | Yellow / Green | High (30-80 Ohm) |
| Grounding | Protective outline | Green with a stripe | Connected to the body |
What to do if the colors of the wires do not match the table?
Always rely on the terminal markings on the compressor and the readings of the multimeter, and not on the color of the insulation. Manufacturers may use non-standard color coding in different series of equipment.>
Step-by-step instructions for installing relays
The installation process begins with dismantling the old part. Carefully remove the retaining bracket or bar that holds the relay to the compressor housing. If the relay is tight, wiggle it slightly from side to side, but do not apply excessive force to avoid breaking the ceramic compressor terminals. Disconnect the power wires, having previously memorized or photographed their connection diagram.
Take a new relay and make sure that its seat exactly matches the terminals of your compressor. It should fit tightly and with a slight click. If you are using a universal relay, the kit may come with adapter blocks or terminals - choose those that match the geometry of your motor. Connect the wires to the corresponding relay contacts according to the markings.
After mechanical installation and connection of the wires, return the retaining bracket to its place. Make sure that the relay is located exactly in the position in which it was originally (usually the arrow on the body points up UP). Violation of the orientation can lead to incorrect operation of the mechanism or its jamming.
Now you can proceed to testing. Plug in the refrigerator. You should hear the compressor start confidently without long beeps or repeated clicks. If the motor starts running smoothly and after some time cold appears in the chamber, it means replacing the starting relay it was successful.
⚠️ Attention: If after replacing the relay the compressor hums, but does not start, or immediately knocks out the circuit breaker, immediately turn off the power. Perhaps the problem is not in the relay, but in the interturn short circuit of the windings or the compressor wedge.
Frequent errors and precautions
When repairing refrigerators on their own, beginners often make mistakes that nullify all efforts. One of the most common is ignoring the inspection of the compressor itself. Installing a new relay on a faulty engine will only lead to re-burning of the part. Therefore, diagnosing the motor windings is a mandatory step.
Another mistake is using a relay from another refrigerator model “by eye”. Even if the connectors are the same, the current characteristics may differ. This will lead to the relay being either constantly on (overheating of the windings) or not turning on at all. Always use catalog numbers to select analogues.
It is also worth mentioning the cleanliness of the contacts. Attempting to install a relay on oxidized or burnt compressor terminals will result in transient resistance, heating, and eventual melting of the plastic relay housing. Cleaning the contacts is a simple but necessary procedure.
Questions and answers (FAQ)
Is it possible to start a compressor without a start relay?
Theoretically, you can start the motor by manually applying voltage to the starting winding for a short time, but this is extremely dangerous and is not recommended. Without a relay, the engine will not be able to reach operating mode and will quickly burn out due to overheating of the windings or thermal protection will trip.
Why does a new relay burn out a few days after installation?
This may indicate several problems: incorrect orientation of the relay (if it is inductive), high voltage in the network, malfunction of the compressor itself (interturn short circuit) or the use of a low-quality analogue with unsuitable current characteristics.
What is the difference between the relay for Atlant and Indesit refrigerators?
The main difference is the fastening design and the location of the contacts. Relays Atlant often have a vertical arrangement of contacts, while European compressors (Indesit, Ariston) are characterized by a horizontal arrangement. Electrically they may be similar, but mechanically they are not compatible without adapters.
How can you tell that it is the relay that has burned out, and not the compressor?
If you hear a click, a short buzz and a second click when you turn it on, most likely the problem is in the relay or the compressor wedge. Ring the motor windings: if the resistance between any contacts is zero (short circuit) or infinity (open), then the compressor is faulty. If the windings are intact, change the relay.