How to start the electric motor of a refrigerator: diagnostics and diagrams

A sudden stop of the compressor is always a stressful situation for the owner of household appliances, because it threatens food damage and the need for urgent repairs. Most often, the problem lies not in the motor itself, but in its starting circuits, and knowing how to properly start a refrigerator electric motor can save you from buying a new expensive unit. In this article, we will analyze the design of single-phase asynchronous motors used in household refrigerators, and consider methods for forcing them to turn on for diagnostics or temporary operation.

Before taking up the tools, you need to clearly understand that electric motor your refrigerator operates from a single-phase 220 volt network, but it requires a phase shift to create torque. This shift is provided by the starting winding and a special starting device, the role of which is most often played by a thermal or electromagnetic relay. If you hear the hum of the motor, but the shaft does not turn, or the silence is interrupted only by clicks, it means that the starting system has failed, and you have to figure out the reasons.

Modern models, such as Indesit, Atlant or Bekoare often used compressors with increased requirements for starting currents, therefore standard methods of “revival” may differ from the old Soviet ZIL or Biryusa units.

The principle of operation and design of a single-phase motor

The basis of any refrigeration unit is a hermetic compressor, inside which the electric motor i is located piston group. The engine has two main windings: working (main) and starting. The working winding occupies two-thirds of the stator slots and has a thicker wire, providing the main magnetic field during operation. The starting winding is wound with a wire of smaller cross-section and is turned on only at the moment of start, creating the necessary torque.

The key element here is the starting relay, which automatically turns off the starting winding after the rotor reaches about 75% of the rated rotation speed. Older models used relays with a posistor (thermistor), which was heated by current and opened the circuit, while more modern or powerful units use electromagnetic relays that respond to the strength of the starting current. If this mechanism jams or burns out, the engine hums, but cannot start.

⚠️ Attention: It is strictly forbidden to leave the engine running with a faulty start relay for more than 3-5 seconds. The windings at this moment consume a huge current (short circuit mode), which will lead to rapid overheating of the insulation and an interturn short circuit, after which the motor can only be thrown away.

To understand the processes occurring inside, it is worth considering the differences in designs. For example, compressors Danfoss are often equipped with RT-type relays, where the posistor is located in a separate housing, and in models LG or Samsung the starting circuit can be integrated into a common control board, although the principle of separation of the windings remains unchanged. Understanding which winding is responsible for what is critically important when testing with a multimeter.

Required tools and safety measures

Before starting any diagnostic work or attempting to start compressor directly, it is necessary to prepare the appropriate tools. You do not need complex industrial equipment, but a basic electrician's kit is required for safe work and obtaining reliable results of resistance measurements.

• 🔧 Multimeter (tester) - necessary to check the integrity of the windings and the absence of breakdown on the housing.
• 🔌 Wires with alligator clips - for temporarily connecting a relay or supplying voltage.
• 🧤 Dielectric gloves - a mandatory element of protection when working under 220V voltage.
• 🔦 Flashlight - for inspecting the insides of the refrigeration cabinet and markings on the relay.

Special Attention should be paid to preparing the workplace. The refrigerator must be disconnected from the network at least 15-20 minutes before starting work so that the capacitors are discharged (if they are in the control circuit) and the freon pressure in the system is stabilized. It is also recommended to remove the rear protective cover of the unit to gain access to the compressor and Ensure that all electrical connections are dry before proceeding.

⚠️ Warning: Never touch the metal parts of the compressor or wires with wet hands. Even a small amount of moisture on the floor or on a tool can become a conductor of current, resulting in severe electrocution.

If you plan to perform live tests (such as checking relay operation), make sure there are no flammable objects around. Sparking of relay contacts is normal, but can be dangerous in oil vapor or dust environments. Always keep a fire extinguisher on hand, although when working correctly with electrical appliances with a power of up to 1 kW, the risk of fire is minimal.

Diagnostics of the serviceability of electric motor windings

Before trying to start the engine, you need to make sure that it is generally suitable for work. The first step is always a visual inspection and “testing” of the windings with a multimeter in resistance (Ohm) measurement mode. The compressor body usually has three terminals covered with a plastic cover: two upper and one lower (or arranged in a triangle).

Remove the wires and terminals, then measure the resistance between pairs of contacts. You need to find three values: the resistance between the working and starting windings, the resistance of the working winding and the resistance of the starting winding. The sum of the two smaller resistances should equal the largest value (resistance between the extreme terminals). If the multimeter shows “infinity” (open circuit) or “zero” (short circuit), then electric motor it is faulty and requires replacement.

It is also critical to check that there is no breakdown on the housing (“land”). Set the multimeter to diode testing mode or high resistance measurement mode. Press one probe against the stripped metal of the case (where there is no paint), and with the other touch each of the three contacts in turn. The device should show infinite resistance. Any value, even a few Megaohms, may indicate an insulation failure, which is fatal during operation.

It is important to consider that different manufacturers have values resistances may vary. For example, for compressors Whirlpool the resistance of the starting winding may be higher than for analogues from Embraco. If the values ​​are significantly out of range (for example, 1-2 Ohms or thousands of Ohms), this is a sure sign of an internal malfunction.

Connection diagram and replacement of the starting relay

If the windings are intact, but the engine does not start, the problem almost certainly lies in the starting relay. This device fits directly onto the compressor terminals. To replace or check it, you need to remove the relay, first photographing or remembering the position of the wires. It is usually held on by latches or a bracket.

Inside the relay you will find a contact group and possibly a posistor (round tablet) or a coil with a core (in electromagnetic relays). Check the contacts for carbon deposits. If the relay is electromagnetic, you can shake it near your ear: if you hear the ringing of a falling part, it means the mechanism is destroyed. For posistor relays, it is critical to let them cool for 5-10 minutes after each turn on, otherwise they will not work again.

When installing a new relay, make sure that it matches the markings of the old one. There are few universal solutions, although there are adapted kits for common models Indesit i Atlant. The connection must be rigid, the wires should not dangle, since the vibration of a working compressor can cause sparking and repeated failure.

⚠️ Attention: When installing the relay, strictly observe the “UP-DOWN” orientation. There is always an arrow or the inscription UP on the relay body. If you install the relay upside down, gravity will not allow the core to fall and break the starting winding circuit, which will lead to the engine burning out in a matter of seconds.

Methods of forced starting of the compressor

There is a situation when you need to start the compressor directly, bypassing standard relay, for example, for pumping out freon or checking the operation of hydraulics. To do this, use a special start button or a circuit with a capacitor. Remember that this is a temporary diagnostic measure, and not a repair method for further operation.

The essence of the method is to manually apply voltage to the starting winding at the moment the working winding is turned on. You will need a non-latching button (for example, from a doorbell). The connection diagram is simple: one wire from the network goes to the working winding constantly, and the second wire is fed through the button to the starting winding. By pressing the button, you simulate the operation of the starting relay.

Connection diagram for starting:
1. Phase (L) -> Compressor common contact.
2. Zero (N) -> Operating winding of the compressor.
3. Phase (L) -> Button -> Start winding of the compressor.

The algorithm of actions is as follows: turn on the power, immediately press the start button (hold for 1-2 seconds), the engine should start and hum smoothly. As soon as the speed is gained, release the button. If you release too early, the motor will stop; if you release too late, the starting winding will burn out. This method requires skill and caution.

Is it possible to start a compressor without a relay forever?

Theoretically, you can use a button, but this is extremely dangerous and inconvenient. There are special starting devices (ROMs) that automatically give an impulse at start, but their installation requires deep knowledge of electrical engineering. The standard relay is more reliable and safer.

Typical errors and reasons for unsuccessful startup

Even with correct diagnostics, startup may fail. One of the most common mistakes is ignoring the condition of the refrigeration circuit. If there is high pressure in the system (for example, after a long period of inactivity or when trying to start in a warm room), the starting torque of the engine may not be enough to overcome the freon pressure.

They also often forget about the thermal relay, which is in the open circuit. If it is faulty (open), the current simply will not reach the windings. Check its integrity with a multimeter: when cold it should “ring” briefly. If the circuit is open, the engine will not start, no matter how many times you change the starting relay.

• ❌ Trying to start with high pressure in the system (bleeding the freon is required).
• ❌ Using wires of too small a cross-section, which causes a voltage drop.
• ❌ Ignoring the heating of the compressor (you cannot start a hot motor).
• ❌ The winding leads are mixed up (the phase is supplied to the wrong terminal).

If the compressor starts, but operates with strong vibration or noise, the alignment of the internal mechanisms may be disturbed or the motor suspension springs inside the hermetic unit may have broken. In this case, no electrical repair will help - a complete replacement of the unit is required.

FAQ: Frequently asked questions

Is it possible to start a three-phase motor from a single-phase 220V network in a refrigerator?

In household refrigerators there are three-phase motors are practically not used. If you come across an industrial unit, then starting is possible through a “triangle” or “star” circuit using capacitors, but for a home refrigerator this is irrelevant and requires complex modifications.

Why does the compressor hum for 5 seconds and turn off?

This is the thermal protection triggered. The engine tries to start, draws high current, gets hot, and the thermal relay opens the circuit to prevent a fire. Reasons: jammed piston, high freon pressure or faulty starting relay.

What capacitor is needed for starting if there is no standard relay?

For refrigerator engines, starting capacitors with a capacity of 30 to 50 uF are usually used for a voltage of at least 300V (preferably 450V). The exact rating depends on the power of the specific motor indicated on the nameplate.

Is it dangerous to start a compressor without freon?

Short-term operation (1-2 minutes) to check the operation of the piston group is acceptable. However, long-term operation without refrigerant is dangerous, since freon and oil in the system also participate in cooling the motor windings. Without them, the motor may overheat faster than usual.

Is it possible to restore a burnt winding yourself?

Theoretically, rewinding is possible, but in practice it is not economically feasible. The cost of work and materials will approach the price of a new compressor, and the quality of sealing and balancing in a garage environment cannot be ensured. It is recommended to replace the entire assembly.