Replacement or self-installation compressor in a household refrigerator is one of the most difficult procedures in the home repair of household appliances. This is due not only to the need for special tools for working with copper pipes and refrigerant, but also to the high risk of electric shock if the contacts are connected incorrectly. Refrigeration unit works under high voltage, and errors in the connection diagram can lead to instant failure of an expensive motor or even a wiring fire.
Before proceeding with manipulations with the electrical part, it is necessary to completely de-energize the device by unplugging the plug from the socket. Any work under voltage is strictly prohibited, since the capacitors in the starting circuit can retain a charge that is dangerous to life. In this article we will analyze in detail the design of the start-up relay, the color marking of the wires and the sequence of actions for the safe restoration of the refrigeration circuit It is worth understanding that modern inverter models may have a fundamentally different motor control architecture, different from classic linear compressors. If your refrigerator is equipped with a.
It is worth understanding that modern inverter models may have a fundamentally different motor control architecture, different from classic linear compressors. If your refrigerator is equipped with a No Frost or electronic temperature control system, the circuit may include additional controllers and sensors that require professional diagnostics. However, for most standard single-chamber and double-chamber models, the principle of supplying voltage to the windings remains similar and is based on physical laws proven over decades.
Design and purpose of a start-up protection relay
The key element in the motor power supply circuit is the start-up relay, which is often called a starter. This small plastic block, mounted on the side or bottom of the compressor housing, performs two critical functions: it provides short-term voltage to the starting winding to generate torque, and it protects the motor from overcurrent. Inside the device there is a electromagnetic coil moving contact that opens the starting winding circuit immediately after the rotor reaches the required speed.
The design also contains a thermal relay, which is a bimetallic plate. When the motor overheats or the shaft is jammed, this plate bends and physically breaks the electrical circuit, preventing the winding insulation from burning. Protective mechanism triggers automatically, and after the compressor cools down, the contact closes again, allowing you to try to start the unit again. It is the characteristic click, which is sometimes heard when the refrigerator is operating, that often indicates that this fuse has tripped.
Incorrect orientation of the relay during installation is a common mistake for beginners. There is usually an arrow or marking UPon the device body indicating the correct position in space. If you install the relay upside down, gravity will not allow the contacts to open and close correctly, which will cause the motor to hum and subsequently fail. Always check the position of the parts before final fixation.
Why does the relay sometimes spark?
Inside the start relay there is a moving contact that opens the circuit under load. At this moment, an electric arc inevitably occurs. Over time, carbon deposits form on the contacts, increasing resistance, which can lead to sticking or, conversely, to lack of contact. Regular cleaning of the contacts with fine sandpaper can extend the life of the relay, but it is better to replace it with a new one.
Connection diagram and color coding of wires
To connect the power correctly, you must clearly understand which wires are responsible for what. The standard circuit uses three main wires running from the thermostat and start relay to the compressor terminal block. Typically these are wires of black, red (or brown) and yellow-green colors. Black wire most often it is phase and supplies voltage directly to the working winding of the motor through the thermal relay contacts.
The red or brown wire connects the starting relay to the starting winding compressor. It is through this channel that the impulse to start the engine is supplied. The third wire, which has yellow-green insulation, is grounding and is connected to the metal body of the unit to ensure electrical safety. In older Soviet-made models, the color scheme could be different, so you should always rely on the electrical circuit diagram located on the inside wall of the refrigerator or in the technical data sheet.
- 🔴 Phase wire (L) - usually black or white, goes from the thermostat to the relay.
- 🟢 Grounding (PE) - yellow-green, attached to the motor housing.
- 🔵 Zero (N) - blue wire, goes directly to the common terminal of the windings.
- 🟠 Starting wire - goes from the relay to the starting winding inside the motor.
When assembling the circuit, it is important not to confuse the contacts on the compressor terminal box itself. They are arranged in a triangle or in a row and have letter designations: C (Common, common), R (Run, working winding) and S (Start, starting winding). An error in connecting the wires to these terminals will result in the motor humming but not starting, or the starting winding burning out.
Tools and safety measures during work
Working with the electrical components of the refrigerator requires a minimum set of tools and adherence to strict safety rules. First of all, you will need a working multimeter to check the voltage and continuity of the circuits. Without this device, connecting “at random” is tantamount to a lottery with a high risk of losing in the form of burnt equipment. You also need screwdrivers with insulated handles, pliers and, preferably, dielectric gloves.
Particular attention should be paid to the condition of the wire insulation. In older refrigerators, the insulation often deteriorates and cracks, creating the risk of a short circuit. Before assembling the circuit, carefully inspect all visible wiring areas. If damage is found, it must be insulated using heat shrink tubing or high-quality insulating tape designed for high temperatures.
⚠️ Attention: Never measure with a multimeter in resistance (ohms) mode on a live circuit. This is guaranteed to damage the tester. First, make sure there is no current, then test the circuits, and only after that apply power to check operation.
When working with capacitors, if they are present in the circuit of your refrigerator (often found in two-phase motors), you must first discharge them. The capacitor can retain its charge for a long time after the device is turned off. Short-circuiting the terminals with an insulated-handled screwdriver will help avoid a nasty electric shock. Electric capacity in such circuits can be large enough to cause serious injury.
Step-by-step instructions for connecting the compressor
The connection process begins with dismantling the protective casing located in the lower rear part of the refrigerator. Removing the cover gives you access to the compressor and start relay. Carefully remove the plastic relay housing by pulling it down or releasing the latches to release the contact group. Before disconnecting the wires, it is recommended to take a photo of the original position or sketch the diagram so as not to get confused during assembly.
Next, you need to clean the contacts on the wires if they are oxidized or burnt. Use fine sandpaper or a file, but be careful not to damage the copper core itself. If the wire is broken at the very base, it will have to be extended using twisting followed by soldering for reliability. Simply twisted wires in a vibrating refrigerator will quickly oxidize and lose contact.
☑️ Check before starting
Assemble the circuit in reverse order: first connect the wires to the relay terminals, then put the relay on the compressor terminals until a characteristic click is heard. Make sure that the wires are not stretched or touching hot parts of the compressor or sharp metal edges. After assembling all the electrical parts, you can plug in the refrigerator. Operation is considered normal when the motor starts 1-2 seconds after the relay clicks and runs evenly, without strong vibration.
The table below shows typical winding resistance values for serviceable compressors of various capacities. This data will help you check the multimeter readings.
| Winding type | Resistance (Ohm) | Wire color (typ.) | Purpose |
|---|---|---|---|
| Operating (Run) | 10 - 25 Ohm | Black / White | Main operation |
| Start | 20 - 40 Ohm | Red / Brown | Engine start |
| Common | Sum R+S | Blue / Green | Common zero |
| Case | Infinity | - | Dielectric insulation |
If after switching on you hear a hum, but the compressor does not start, and after a few seconds you hear a shutdown click - there is a problem may be a stuck relay contact or low voltage in the network. In this case, you should not restart immediately. Let the device cool for 10-15 minutes, check the contacts again and only then try again. Frequent attempts to start "head-on" can completely damage the starting winding.
Diagnostics of electrical faults
One of the common problems is an interturn short circuit in the motor windings. This condition is difficult to diagnose visually, but the multimeter may show an abnormally low resistance that differs from the rated values. If there is an interturn short circuit, the compressor can start, but will operate with overheating and consume a current higher than the rated one, which will ultimately lead to the thermal relay tripping or the wiring burning out.
It is also worth checking the integrity of the thermostat. If the circuit breaks in this section, the voltage simply will not reach the compressor. Ring the thermostat contacts: in the “on” position they should ring briefly. The contacts in the plug or socket itself often oxidize, which creates additional resistance and a voltage drop that is insufficient for a reliable start of the motor.
- 🔍 The compressor hums, but does not spin - the starting relay is faulty or the shaft is jammed.
- 🔥 The motor is hot, but is silent - there may be an interturn short circuit or break.
- ⚡ The machine in the panel knocks out - a short circuit in the circuit or a breakdown to the housing.
- ❄️ The refrigerator does not turn on at all - check the circuit from the socket to the thermostat.
It is important to consider that in modern models with electronic control the diagnostic module can block starting the compressor if any of the sensors (temperature, defrost, door position) malfunctions. In such cases, simply replacing the relay or wires will not help - you need to read error codes through the service mode.
Features of connecting inverter compressors
Inverter refrigerators, such as models from LG, Samsung or Whirlpool, have a fundamentally different engine power system. Instead of the classic starting relay and thermostat, an inverter board is used here, which converts the alternating current of the network into direct current, and then again into alternating current, but with a variable frequency. This allows you to smoothly regulate the speed of rotation of the compressor shaft, saving energy and reducing noise.
It is impossible to connect such a compressor directly to a 220 volt network - it will simply burn out. To diagnose and start outside the refrigerator, a special test bench or inverter control unit is required. The connection of wires in such systems is carried out through connectors with multiple contacts, where, in addition to phase and zero, there are communication lines with the sler and control signals.
⚠️ Attention: An attempt to supply 220V voltage directly to the terminals of the inverter compressor (bypassing the control board) will lead to irreversible damage to the internal windings and magnets. Such motors operate from three-phase voltage generated by an inverter.
When repairing inverter systems, first of all, check the integrity of the stator windings (they must have the same resistance among themselves) and the absence of breakdown on the housing. If everything is fine with the motor, but the refrigerator does not work, the problem most likely lies in the inverter board or control module, which requires professional repair at a service center.
Frequently asked questions (FAQ)
Is it possible to connect the compressor from the refrigerator directly without a relay?
Theoretically, you can start the motor by applying voltage directly to the working and starting windings, but doing this manually is extremely dangerous and ineffective. Without a relay, the starting winding will not turn off after the start, which will lead to its rapid overheating and combustion. In addition, you risk getting an electric shock or dropping a heavy unit. Always use a standard or similar starting relay.
Why does the refrigerator turn on and then immediately turn off after replacing the relay?
This phenomenon is called “cyclic starting”. The reasons may be different: the new starter itself is faulty (stuck or defective), the mechanical part of the compressor is jammed, or thermal protection is triggered due to an interturn short circuit in the windings. It is also worth checking the voltage in the network - if there is a strong drawdown, the motor will not be able to develop the required power to start.
How to determine whether the compressor or relay has burned out?
Ring the windings with a multimeter. If the resistance between any two contacts is zero (short circuit) or infinity (break), the compressor is faulty. If the windings are normal, but the motor hums and does not start, and the relay gets very hot or sparks, the problem is in the relay. Often, replacing the relay is inexpensive and is the first step in diagnosis.
Is an old Soviet refrigerator dangerous for wiring?
Old models can consume significant starting current, which creates a load on the network. If the wiring in the house is aluminum and old, it can get hot at the connections. It is recommended to periodically check the temperature of the plug and socket while the refrigerator is operating. If they get hot, you need to replace the socket with a better one and check the contacts in the junction box.