How to connect a compressor from a refrigerator directly without a relay

In situations where a household refrigerator suddenly stops freezing, and diagnostics indicate a malfunction of the start relay or thermostat, the home technician is faced with the issue of emergency starting the unit. Often there is a need to check the functionality of the motor-compressoritself, excluding secondary elements from the control circuit. Connecting the compressor directly from the refrigerator is a standard procedure for checking the tightness of the system or the operability of the engine, which requires strict adherence to safety precautions and an understanding of electrical processes.

Direct connection allows you to isolate the problem: if the engine starts and runs stably, then the fault lies in an automation system, such as start-up protection relay or temperature sensor. However, if the motor hums but does not start, or knocks out circuit breakers, the problem lies deeper - perhaps a jammed piston group or an interturn short circuit. It is important to understand that the operation of refrigeration equipment bypassing the standard protection is allowed only for a short time to carry out diagnostic work.

Before you begin manipulating electrical wiring, you need to make sure that you have basic knowledge in the field of electrical engineering and have the necessary tools at hand. Working with a voltage of 220 Volts is associated with the risk of electric shock, so ignoring safety rules is unacceptable. In this article we will analyze in detail the connection diagram, methods for checking windings and nuances that will help you safely carry out diagnostics.

Preparation of tools and safety measures

The first stage of any electrical installation work is preparing the workplace and tools. To complete the task of directly starting the compressor, you will need a minimum set of tools that any home handyman usually has. The main tool will be a multimeter to check the integrity of the windings and the presence of voltage, as well as a set of screwdrivers and side cutters.

It is extremely important to ensure the insulation of all connections. The use of electrical tape or heat-shrink tubing is mandatory, as exposed live wires pose a mortal danger. It is not recommended to use twists without subsequent soldering or reliable terminal fixation, especially in conditions of vibration of the operating compressor.

⚠️ Attention: Before starting any work, make sure that the power cord is completely unplugged from the outlet. Residual voltage in capacitors or circuits may result in electric shock. Work only with dry hands and on a dry surface.

For ease of operation and the ability to control the startup process, it is recommended to assemble a temporary circuit using a button or toggle switch. This will allow you to control the moment of power supply and quickly turn off the device in case of an emergency, for example, when smoke or strong buzzing appears without rotating the shaft.

• 🔧 Multimeter or tester for continuity testing
• 🔌 Power cord with plug and power button
• 🧤 Dielectric gloves for hand protection
• 🔩 Set of screwdrivers and pliers for dismantling
• 🧱 Insulating materials (insulating tape, cambrics)

The design and principle of operation of the motor-compressor

To correctly connect the device, you need to understand its internal structure. The refrigerator motor-compressor is a sealed unit in which the electric motor and compressor part are located in a common housing filled with refrigerant and oil. The electric motor is most often asynchronous with a squirrel-cage rotor.

The motor stator has two main windings: working and starting. The working winding has a larger wire cross-section and lower resistance; it is designed for continuous operation. The starting winding is made of a thinner wire, has a higher resistance and is turned on only at the moment of starting to create a rotating magnetic moment.

In the standard circuit, these windings are switched by a starting relay. When the rotor is stationary, the resistance of the working winding is small and the current is high. The electromagnetic field of the relay closes the contacts of the starting winding. After gaining speed, the current drops, the relay opens, and the engine continues to operate only on the working winding. With a direct connection, we will have to simulate this process manually or using a circuit.

Why can’t we leave the starting winding on all the time?

The starting winding is designed for short-term operation (1-3 seconds). If you leave voltage on it, it will quickly overheat, the insulation will melt, and an interturn short circuit will occur, which will lead to the engine burning out.

There are three terminals on the compressor housing that correspond to the ends of the windings. In older models, they may not have markings, so their identification is done by testing them with a multimeter. Understanding which pin does what is the key to a successful startup.

Identification of contacts and winding continuity

Before applying voltage, it is necessary to accurately determine the purpose of the contacts on the compressor terminal block. They are usually arranged in a triangle. In modern models, they can be signed with the letters C (Common - general), R (Run - working) and S (Start - starting), but you should not rely only on the marking, as it can be erased or applied erroneously.

The identification process begins with a search common point. To do this, switch the multimeter to resistance measurement mode (Ohm) and ring the pairs of contacts one by one. The pair with the greatest resistance is the ends of the starting and operating windings. The third contact, not involved in this pair, is the common terminal.

Next, we measure the resistance between the common terminal and the two remaining ones. The contact, the resistance to which will be less, refers to the working winding. Contact with high resistance - to the starting one. These values may vary depending on the engine power, but the relationship is always the same: the working winding has less resistance than the starting winding.

Pay special attention to checking for breakdown on the housing. Press one multimeter probe to the cleaned area on the body (where there is no paint), and touch each of the three terminals with the other. The device should not show any conductivity. The presence of resistance indicates a violation of tightness and insulation, which makes the operation of such a unit dangerous.

Direct connection diagram via a button

The safest and most controlled way to start the compressor directly is to use a button without locking or a toggle switch. This circuit allows you to apply voltage to the starting winding only at the moment of start, simulating the operation of a relay. To implement this method, you will need a button with normally open contacts.

The connection diagram is as follows: the phase wire from the network is connected to the starting terminal through the button, and is also permanently connected to the working terminal. The neutral wire is connected to the common terminal. Thus, when the button is pressed, voltage is applied to both windings, the engine starts, and after releasing the button, it continues to work only on the working winding.

Important observe the time interval for pressing the button. Keep the starting winding energized for no more than 1-2 seconds. If the engine is working properly, it will enter operating mode almost instantly, changing the nature of the sound from a hum to the smooth hum of a running motor.

⚠️ Attention: Do not use a locking button to connect the starting winding! If you forget to turn it off, the starting winding will burn out in a matter of seconds, and the compressor will fail completely.

If you don’t have a button, you can use a circuit with a capacitor, but it requires an accurate calculation of the capacitance and is less convenient for diagnostics. The button method is the “gold standard” for quickly checking the motor in a workshop or at home.

Starting the compressor and diagnosing faults

After assembling the circuit, you can begin a test run. Make sure the compressor is placed on a level surface, preferably a rubber mat, to dampen vibration. Plug the plug into the socket, press the start button and release it after 1-2 seconds.

If the engine is working properly, you will hear a confident start and a smooth hum. Air will begin to escape from the outlet tube, which indicates the operation of the piston group. At this moment, you can check the pressure by connecting a pressure gauge station to the fittings, if the purpose of diagnosis is to check compression.

• 🔊 The engine hums, but does not start - perhaps the starting winding is jammed or faulty.
• 🔥 The engine starts and immediately knocks out the machine - short circuit in windings or interturn.
• 💨 No air comes out of the tubes - a violation of the housing seal or breakage of the valves.
• ⚡ Sparking in the contact area - poor contact or oxidation of the leads.

In a situation where the motor hums, but the shaft does not turn, sometimes the wedging method helps. To do this, voltage is applied to the starting winding for a longer time (up to 5-7 seconds), trying to create more torque. However, this method is risky and is applicable only to older models, which we don’t mind.

Pay attention to the temperature of the case. When operating “directly” without regular airflow and in conditions where the refrigerator is not filled with food (heat-storing mass), the compressor may overheat faster than usual. Do not keep it turned on for diagnostics for more than 10-15 minutes.

Frequent errors and typical connection problems

One ​​of the most common errors is confusion between the working and starting windings. If you apply operating voltage to the starting winding as the main winding, the engine may hum, heat up, but not develop the required speed, or start in the opposite direction (which for a refrigerator compressor is not critical in the direction of rotation, but is harmful to the lubrication system).

Also often, craftsmen forget about the need for grounding. The compressor housing is metal, and if the insulation inside the hermetic unit is damaged, a potential may appear on it. Touching such a unit during operation may result in electrical injury. Always use grounded outlets or ground the chassis separately.

Another problem is using wires that are too thin for connections. Compressor starting currents can be 3-5 times higher than the rated current. A thin wire may melt or cause a voltage drop, due to which the motor will not be able to develop the required power to start.

⚠️ Attention: Technical characteristics of compressors of different brands (Danfoss, Secop, LG, Atlant) may differ. Always check the technical documentation for your specific model, if available, especially regarding inrush currents and required capacitor capacity.

Don’t forget about the condition of the oil. If the compressor has been lying on its side for a long time, oil may have drained into the circuit or into the cylinder. Starting such a unit can lead to water hammer. Let it stand in a vertical position for at least 24 hours before checking.

Is it possible to start a compressor without a starting winding?

Theoretically, if you manually spin the motor shaft to high speeds, it can start on one working winding. However, this method is not applicable for a refrigerator compressor, since it is impossible to manually develop a sufficient speed of rotation of the shaft with the piston group. In addition, this creates a risk of injury.

How long can you keep the compressor turned on when checking?

For initial diagnosis, 1-2 minutes of operation is enough. This will allow you to evaluate the nature of the sound, check for compression and make sure there are no short circuits. Long-term operation (more than 15 minutes) without a standard cooling and protection system can lead to overheating and deformation of parts.

What to do if the compressor hums but does not start?

First check the voltage in the network - if the voltage is low, the motor will not start. If everything is fine with the network, try increasing the time of applying the pulse to the starting winding (up to 3-4 seconds). If this does not help, most likely, there is a mechanical jamming of the piston group or severe burning of the contacts inside the relay (if the test is carried out with it).

Is connecting directly to the electronics of the refrigerator dangerous?

Yes, if the refrigerator has a complex electronic control board, directly connecting the compressor bypassing it is safe only for the motor itself. However, if you plan to use stock electronics in the future, make sure that you have not damaged other circuits during the “direct” test. For full operation of the refrigerator, a relay or its electronic analogue is necessary.