The situation when the refrigerator suddenly stops cooling, and the compressor is silent or makes only a quiet humming sound, often confuses the owner. In most cases, the reason for the silence of the unit is the failure of the starting relay or a violation of the electrical contact in the control circuit. To understand whether it is alive compressor or the problem lies in the electronics, technicians use the method of directly starting the engine, bypassing the standard protection and automation circuits.
Direct connection of the motor to the electrical network is an effective diagnostic test that allows you to determine the performance of the heart of the refrigerator in a matter of minutes. However, this process requires strict adherence to safety precautions and a clear understanding of the electrical circuit. Incorrect actions can lead to electric shock or final breakdown of the unit, so approach the procedure with maximum responsibility.
In this article we will analyze the trigger mechanism in detail, consider a step-by-step algorithm of actions and explain how to safely apply voltage to the motor windings. You will learn what tools are required for the job and how to interpret the test results.
The design of the starting mechanism and the principle of operation
Before you start manipulating the wires, you need to understand how the standard circuit for switching on a single-phase asynchronous motor used in household refrigerators works. The compressor has two main windings: starting and working. The working winding creates the main magnetic field for rotation of the rotor, and the starting winding is needed only at the moment of start in order to create the initial torque.
The starting relay is responsible for distributing the current between these windings. In older models it could be electromechanical (with a heavy copper core), while in modern ones a posistor is more common. A posistor is a ceramic element that, when heated by current, sharply increases its resistance, essentially breaking the starting winding circuit. If this element burns out or the contacts stick, the motor does not receive the necessary impulse to start.
What is the difference between different types of relays?
In posistor relays, current flows through a ceramic element, which heats up and opens the circuit in 1-3 seconds. Electromechanical (induction) relays use a movable core, which, under the influence of current in the working winding, rises and closes the contacts of the starting winding, and when the rotor accelerates, the current drops and the core drops, opening the circuit.
When starting directly, we artificially imitate the operation of a working relay, applying voltage to both windings at once at the time of start, and then We leave power only at work. This requires precise determination of the terminals on the contact group of the compressor, since an error in the connection can lead to a short circuit or overheating of the windings.
Necessary tools and precautions
Working with high voltage electricity (220V) does not tolerate negligence. Before starting any work, make sure that you have all the necessary tools at hand. The lack of suitable devices can not only complicate the task, but also make the process unsafe for life and health.
For diagnostics and direct start-up you will need:
- 🔧 Screwdrivers (phillips and flat) for dismantling the casing and removing the relay.
- 🔌 Power cord with plug and bare ends of wires for connecting to the network.
- 📏 Multimeter for testing windings and checking resistance.
- 🧤 Dielectric gloves for protection against accidental electric shock.
- 💡 Test lamp or voltage tester to check the presence of a phase.
⚠️ Attention! All manipulations to connect wires to the contact group should be carried out only with the refrigerator disconnected from the network. Voltage is supplied exclusively at the time of the final test, when all connections are securely fixed and insulated.
Particular attention should be paid to insulation. The temporary connections you make for the test should not touch each other or any metal parts of the case. Use electrical tape or special alligator clips with insulated handles. Do not allow moisture to get on electrical components during operation.
Dismantling and identifying compressor contacts
The first stage of work is access to the compressor. It is usually located at the bottom rear of the refrigerator and is covered with a metal or plastic casing. Remove the cover by unscrewing the mounting screws or releasing the latches. A black cylindrical or pear-shaped unit will appear in front of you - this is the motor-compressor.
At the end of the compressor there is a contact group covered with a plastic box. Carefully remove this box, having first disconnected from it the wires coming from the thermostat and the start relay. Now you need to determine which pin on the contact strip is responsible for what. Standard markings are often applied directly to the plastic or metal next to the terminals:
- 🔵 C or Common — common wire.
- 🔴 R or Run —working winding.
- 🟡 S or Start — starting winding.
If the markings are erased or missing, which often happens on older models, you will have to use a multimeter. The resistance between the common contact and the working winding is always less than that between the common and the starting winding. The resistance between the starting and working windings will be equal to the sum of the two previous values. This is a physical law that allows you to accurately identify the conclusions.
☑️ Check before starting
After identifying the terminals, it is recommended to write down their location or take a close-up photograph. This will help avoid confusion when you need to quickly assemble the circuit for launch. An error in the identification of starting and working windings can lead to the motor humming but not starting, or the thermal protection triggering.
Scheme of direct connection to the network 220 Volt
The essence of the direct starting method is to briefly apply voltage to the starting winding simultaneously with the working one. As soon as the motor shaft begins to rotate, the starting winding must be turned off, leaving power only on the working one. In a factory relay this happens automatically, but we will have to do it manually or using a button.
To implement the circuit, you will need a two-wire cord. One wire (phase) will be connected to the common contact C. The second wire (zero) will go to the contact of the working winding R. To start, you need to briefly connect the contact of the starting winding S with the phase wire (contact C). It is most convenient to use a button without fixing or simply touch the contact with the wire for a split second.
| Contact on the compressor | Designation | Where to connect the phase (L) | Where to connect the zero (N) |
|---|---|---|---|
| General | C (Common) | Yes (permanently) | No |
| Worker | R (Run) | No | Yes (permanently) |
| Launcher | S (Start) | Yes (short-term) | No |
| Case | Ground | Categorically no | Certainly no |
It is important to follow the sequence: first assemble the circuit “Zero - Working winding” and “Phase - Common contact”. Only after making sure that these connections are reliable, briefly touch the starting contact with the phase wire. If the compressor is working properly, you will hear a characteristic starting click and a smooth hum of the running motor.
Diagnostics of faults based on startup results
The behavior of the compressor during direct start provides comprehensive information about its technical condition. If the engine starts and runs smoothly, then the problem is definitely not there. Most likely, the start relay has failed, the thermostat has burned out, or the contact in the defrost circuit has been broken.
If a loud buzzing sound is heard when voltage is applied, but there is no rotation, several options are possible. Most often, this indicates jamming of the piston group or severe wear of mechanical parts. Sometimes the so-called “shock wave method” helps - a light but sharp blow with a wooden mallet on the compressor body at the moment the voltage is applied can move the jammed parts, but this is a temporary measure.
⚠️ Attention! If the compressor hums but does not start, do not keep the voltage applied for more than 3-5 seconds. The windings will begin to rapidly heat up, which can lead to an interturn short circuit and the final failure of the motor.
If the motor starts, but after 10-20 seconds of operation it turns off with a characteristic click (even without a connected thermostat), this may indicate a breakdown of the windings on the housing or a malfunction of the internal thermal relay You can check the breakdown with a multimeter by measuring the resistance between any contact and the copper tube of the housing - it should be infinite.
You should also pay attention to the smell. If you smell burnt insulation or burning when starting, further experiments are pointless - the engine has burned out. In such a situation, replacement of the compressor is required, since rewinding at home is economically impractical and technically difficult.
Temporary operation and replacement of relays
Direct start is a diagnostic procedure, and not a method of permanent operation. It is strictly forbidden to leave the refrigerator operating in a wire-to-wire manner. The standard relay provides not only starting, but also overload protection. Without it, if there is a power surge or the piston jams, the motor will burn out in a matter of minutes.
If the diagnostics showed that the compressor is working, you need to replace the starting relay. Remove the old relay and go to a parts store with a photo or label of it. Relays are selected strictly according to motor power and compressor type. There are no universal solutions here, although there are combination relays suitable for a wide range of models.
When installing a new relay, make sure that it fits tightly and the contacts do not loosen. The vibration during operation of the refrigerator is high, and poor contact will lead to sparking and re-burning of the part. After assembly, plug in the refrigerator and check the first cycle of operation: the motor should start, run for the specified time and turn off.
In some cases, if the original relay cannot be found, it is possible to install an analogue with the same characteristics, but this requires re-soldering the contacts or adapting the seat. If you do not have the skills to solder and work with electrical circuits, it is better to order an original spare part or call a specialist.
Is it possible to start a refrigerator without a relay forever?
No, it is not possible. Operation without a relay will deprive the motor of protection from overheating and overloads. Any jamming or power surge will burn out the winding. In addition, without a relay there will be no break in the starting winding circuit, which will lead to its rapid combustion in operating mode.
Why does the compressor hum but does not start?
There may be three reasons: the mechanics (piston group) are jammed, the starting winding is burned out, or the starting device is faulty. If the motor starts during direct "assisted" starting, then the problem is in the start relay or the start winding. If it doesn’t start even with help, it’s most likely a mechanical wedge.
What current does the compressor consume when starting?
The starting current can be 3-5 times the rated operating current. For household refrigerators, it can reach 10-15 Amps at the moment of start, so the wiring and socket must be in good working order. That is why it is important not to use thin temporary wires for diagnostics.
Is it dangerous to touch the compressor during operation?
During operation, the compressor gets very hot (up to 70-90 degrees), so it is not recommended to touch it with bare hands - you can get burned. Also make sure that the case is not energized (check with a multimeter before touching), although in working refrigerators the case is grounded or has no potential.