The situation when the refrigerator stops cooling, and the compressor is silent or hums, but does not start, often leaves the owner with a choice: call a technician or try to figure it out on his own. Direct connection of the motor is one of the key diagnostic stages, allowing you to determine whether the unit itself is alive or the problem lies in the control system, thermostat or start relay. Many people mistakenly believe that complex equipment is required for testing, but in reality a minimum set of tools and an understanding of the electrical circuit is sufficient.
However, it is worth immediately defining the boundaries of what is permitted: direct connection of the stator windings is dangerous procedurerequiring strict adherence to safety precautions. An electric current of 220 volts is unforgiving, and the refrigerant inside the system is under pressure. If you are not confident in your abilities or do not have basic skills in working with electrical appliances, it is better not to take risks. However, for enthusiasts who want to revive an old Atlant or Indesit, knowledge of the principles of operation of the electric motor will be extremely useful.
In this article we will analyze in detail the device of a single-phase engine, consider connection diagrams with and without a starting relay, and also discuss the nuances of working with different types of windings. You will learn how to correctly identify contacts, why the starting winding burns out, and how to check the continuity of the circuit with a multimeter. Understanding these processes will help you not only repair the refrigerator, but also correctly select spare parts to replace failed components.
⚠️ Attention: Before starting any diagnostic or repair work, be sure to disconnect the refrigerator from the power supply! Working with live electrical components is deadly.
Design and principle of operation of a single-phase compressor
The heart of any household refrigerator is a hermetic compressor, inside of which an electric motor is located. Unlike industrial three-phase units, home appliances use single-phase asynchronous motors. Their design includes a stator with two types of windings: main (working) and starting. The working winding occupies two-thirds of the stator slots and has a larger wire cross-section, which provides less resistance. It is this that creates the main magnetic field for rotation of the rotor.
The starting winding is located in the remaining part of the grooves and is made of a thinner wire. Its resistance is always higher than that of the worker. The main task of the starting winding is to create an initial torque, moving the rotor from its place. Once the motor reaches about 75% of rated speed, the starting winding should be disconnected. If this does not happen, the current in it increases sharply, which leads to overheating and rapid failure. In old models Zil or Biryusa this was responsible for the starting relay with contacts that opened under the influence of centrifugal force or current.
Modern compressors often are equipped with capacitors or electronic trigger circuits, but the basic principle remains the same. To start the engine, it is necessary to apply voltage to the working winding and briefly to the starting winding. It is this process that is simulated with a direct connection during diagnostics. It is important to understand that constant work on the starting winding is unacceptable.
Why does the starting winding burn out?
The starting winding has high resistance and a thin wire. It is designed for short-term operation (up to 3-5 seconds) at the moment of start. If the relay sticks or does not open the circuit, current continues to flow through the thin wire, causing it to instantly overheat and melt the insulation.
Necessary tools and precautions
Before grabbing the wires, you need to prepare the workplace and tools. You will need a multimeter to test the windings and check the voltage, a set of screwdrivers, pliers and insulating materials. Particular attention should be paid to the wires for connection: they must have a cross-section of at least 0.75 mm² and have good insulation. To temporarily connect contacts, they often use a button with normally open contacts or a special starting relay removed from a faulty unit.
Safety is not just words. The compressor contains oil, which can cause irritation if it comes into contact with the skin and may cause a fire if heated. In addition, if you cut the pipes carelessly, freon may escape. Although modern refrigerants (R600a) are explosive when mixed with air, and older ones (R12) are toxic, at home the risk is minimal in the absence of open flames. However, you should work in a well-ventilated area.
Be sure to use dielectric gloves and shoes with rubber soles. Do not touch the metal parts of the compressor housing while power is applied. Make all connections only with the power cord completely unplugged. After completing the manipulations, make sure that all contacts are securely insulated before plugging the device back into the outlet.
Identifying contacts and checking windings
The most difficult step for a beginner is to figure out which wire goes where. The compressor terminal block usually has three contacts (sometimes four if there is a ground connection). They can be signed with letters or designated by color. The standard marking looks like this: R (Run) - working winding, S (Start) - starting winding, C (Common) - common contact. In some models Liebherr or Bosch the designations may differ, so relying only on letters is not worth it.
First of all, you need to test the windings with a multimeter in resistance measurement mode. Find two contacts between which the resistance is maximum - these are the ends of the starting and working windings. The third contact left "overboard" will be common (C). Next, we measure the resistance between the common contact and each of the other two. The contact with lower resistance is the working winding (R), and the contact with higher resistance is the starting winding (S). Typical resistance values are 10-30 Ohms for the working winding and 30-60 Ohms for the starting winding.
If the multimeter shows one (infinity) between any contacts, then there is a break in the winding and the compressor must be replaced. If the resistance is close to zero, an interturn short circuit has occurred. It is also necessary to check the breakdown on the housing: one probe is placed on the cleaned metal part of the housing (scratches), the second - on each contact in turn. The device should not show any conductivity.
Direct connection diagram via a starting relay
The safest and most correct way to start the compressor is to use a standard or similar starting relay. It automatically switches circuits at the right time. The relay fits directly onto the compressor terminals. The connection diagram is simple: phase and neutral from the network go to the input terminals of the relay, and the output terminals are connected to the motor windings. Inside the relay there is a coil connected in series with the working winding, and contacts that open the starting winding when the speed increases.
When installing the relay, it is important to respect its spatial position. The case usually has an arrow "UP" or "TOP" pointing up. If you turn the relay over, the mechanism will not work and the starting winding will burn out in a matter of seconds. After connecting the circuit, apply power briefly. If the compressor hums but does not start, the relay may be selected incorrectly or the motor itself is faulty (jamming).
The table below shows approximate parameters for selecting a relay for different types of compressors, which will help you navigate when searching for spare parts.
| Compressor type | Power (W) | Relay type | Features |
|---|---|---|---|
| Low speed (old models) | 100-140 | Start-protective (RTK) | Thermal protection built-in |
| Medium-speed (Atlant) | 160-200 | Starting (RSP) | Requires a separate thermal relay |
| High-speed (Inverter) | Varies | Electronic unit | Direct connection is not possible |
| Low-power (mini-bars) | 80-100 | Starting (RTO) | Compact size |
If the compressor starts and runs smoothly, without making any extraneous sounds, then the engine is working properly, and the problem should be looked for in the thermostat, wiring or the relay itself. Do not forget that the thermal protection relay can cool down for several minutes, so repeated startup attempts should be made at intervals of 3-5 minutes.
☑️ Check before starting
Starting without a relay: the "button" method
Sometimes there is no suitable relay at hand, and you urgently need to check the performance of the motor. In this case, you can use the push button method. The essence of the method is to manually simulate the operation of the starting relay. You will need a button without locking (like from a doorbell) or just two insulated wires that can be used to briefly close the contacts.
The connection diagram is as follows: one wire from the network (phase) is connected directly to the contact of the working winding (R). The second wire of the network (zero) goes to the common contact (C). The starting winding (S) is connected in parallel to the working winding, but through a button. That is, one end of the starting winding is connected to the phase wire (at the point of connection to the working winding), and the second - through a button with zero or phase (depending on the implementation of the circuit, the main thing is to apply voltage to the starting winding at the same time as the working winding).
Action algorithm:
- ⚡ Connect the wires to the working and common windings.
- 👆 Press the start winding connection button.
- 🔌 Plug the plug into the outlet (or apply voltage).
- 🚀 As soon as the compressor starts and picks up speed (after 1-2 seconds), release button.
This method requires dexterity and caution. If you hold the button too long, the starting winding will burn out. If you release too early, the motor will not start and will hum. It is critical not to hold the button pressed for more than 3 seconds! Once started, the compressor will work until you turn off the power, since thermal protection is not involved in this circuit (unless it is built into the motor itself).
⚠️ Attention: When starting without a relay, there is no thermal protection. If the compressor seizes or overheats, it will not turn off automatically, which may cause the windings to catch fire. Keep your finger on the power off button!
Fault diagnosis and typical errors
Even with proper connection, the compressor may behave strangely. If the engine hums but does not start, the piston group may be stuck. In old refrigerators, sometimes “swinging” helps: a short-term supply of voltage to the starting winding at the moment of starting (using the button method) can move the piston. However, this is a temporary measure. If the shaft does not rotate, further operation is pointless.
A common mistake is confusion between the working and starting windings. If you mix up the contacts and constantly apply operating voltage to the starting winding, it will burn out instantly. Always double check the resistance before connecting. Another problem is a breakdown on the body. If, when the compressor is operating, it “pinches” with current or knocks out the RCD, it means that the insulation of the windings or internal wires is broken.
It is also worth paying attention to the condition of the contacts. Carbon deposits on the terminals increase resistance and cause heat. Sanding the contacts with fine sandpaper may restore normal operation. If the compressor works, but gets very hot or makes a metallic knocking noise, the internal shock absorbers or valves may have collapsed.
Frequently asked questions (FAQ)
Is it possible to connect a three-phase compressor to a single-phase 220V network?
Theoretically, it is possible using a triangle or star circuit with capacitors, but for refrigerators this is not practical. The power drops, the starting torque is insufficient, and the risk of burning out the motor is high. Household refrigerators are initially designed for 220V.
How long can you keep the compressor turned on during diagnostics?
Without a connected cooling system (condenser and evaporator), the compressor will not be able to effectively remove heat. The maximum operating time in air is 30-40 seconds. Long-term operation without load and cooling will lead to overheating and deformation of the valves.
Why does the compressor start only with a push?
This is a sure sign that the starting winding is not working or is not connected. Either the winding itself has burned out, or the starting relay is faulty and does not send a start impulse. The shaft bearings may also wear out.
Is it dangerous to open the sealed compressor casing?
Absolutely yes. Firstly, there is oil, which upon contact with air quickly oxidizes and loses its properties. Secondly, the tightness is broken and the compressor stops creating pressure. An opened compressor cannot be repaired, only disposed of.