The situation when the refrigerator stops cooling, and the compressor is silent or makes only a quiet click, is familiar to many owners of household appliances. Most often, the first thing to blame is the start-up relay, and this is logical, since it is this unit that fails most often. However, in order to be confident in the diagnosis and not buy a new part in vain, it is necessary to exclude breakdown of the very heart of the unit - compressor. Checking the motor without a relay allows you to determine with high accuracy whether the motor is alive or whether its windings have burned out, which is critical for planning the repair budget.
Direct connection or “testing” of the windings are methods that require strict adherence to safety precautions, since the work is carried out with high voltage and mechanical components under pressure. If you decide to diagnose yourself, you will need a minimum set of tools and a basic understanding of electrical circuits. In this article we will examine in detail how to safely and effectively test the electric motorbypassing the standard starting system, and what nuances should be taken into account when working with different types of compressors.
Before starting disassembly, make sure that the unit is completely disconnected from the power supply. Even briefly touching live contacts can lead to serious consequences. Next, you need to gain access to the bottom of the refrigerator, where the compressor unit is located. It is usually covered with a metal or plastic casing that is secured with latches or screws. Having removed the protection, you will see the motor itself, the capacitor (if your model has one) and that same relay, which we will not touch for now.
Preparation of tools and safety measures
Any work with electrical equipment begins with ensuring your own safety. The main diagnostic tool will be multimeter (tester), which will allow you to measure the resistance of the windings and check for a breakdown on the housing. Without this device, it will not be possible to “ring” the motor qualitatively, since a visual inspection of the wires rarely gives a complete picture of the internal state of the windings. You will also need screwdrivers, pliers and, possibly, electrical tape to temporarily isolate the contacts.
⚠️ Attention: It is strictly forbidden to carry out any manipulations with a refrigerator connected to the network. Before starting work, be sure to unplug the plug from the socket. The residual voltage in the capacitors can persist for several minutes, so let the equipment stand in the switched off state before starting disassembly.
To check the performance of the motor “live”, that is, by trying to start it, you may need a piece of wire with a plug and a button, or a specialized adapter for direct connection. However, for initial diagnosis, only a multimeter is enough. It is also important to prepare the workplace: it should be dry, well lit and free from flammable materials, since the system circulates refrigerant, which under certain conditions can be flammable.
Don't forget about gloves. Although the compressor is cold (unless it has been running recently), there may be oil or grease on its surface. In addition, metal casings often have sharp edges that can easily cause injury. If you plan to remove the relay to get to the motor contacts, do it carefully so as not to damage the fragile terminals. Insulation integrity Wires are a key factor in the safety of further operation.
Visual inspection and access to the contact group
After removing the protective casing you will have a view of the compressor. First of all, pay attention to the appearance of the node. The presence of oil traces around the rod or tubes may indicate depressurization of the system, which automatically makes engine repair pointless - the entire unit will need to be replaced and refilled with freon. Also inspect the wires going to the contact group: they should not be melted, blackened or have visible breaks in the insulation.
To check the motor without a relay, it must be disconnected. The starting and protective relay is usually placed directly on the compressor contacts and secured with a bracket or plastic box. Carefully remove the retaining bracket and pull the relay down. Three contacts arranged in a triangle will open in front of you. These are the inputs to the motor windings. In some models, for example Indesit or Atlant, the design may be slightly different, but the principle of terminal arrangement remains similar.
- 🔍 Carefully inspect the contacts for oxidation or carbon deposits - this may distort the tester readings.
- 🔧 Make sure that the terminals do not wobble and sit firmly in their seats on the motor body.
- 📸 Take a photo of the connection diagram before removing the wires so that you don’t get confused in the colors later.
If visually everything looks normal, you can proceed to measurements. It is important to understand that most household compressors have three terminals: two for the working and starting windings and one common. The master's task is to find this common contact and check the resistance between all pairs. If deep dents or traces of severe overheating (change in metal color) are visible on the case, further diagnostics may be impractical.
☑️ Ready for diagnostics
Diagnostics with a multimeter: searching for opens and short circuits
The most reliable way to understand the condition of the motor is to measure the resistance of its windings. Switch the multimeter to resistance mode (usually indicated as 200 ohms or 2 kohms). Touch the probes to any of the three contacts. If the device shows infinity (one in the most significant digit or the “OL” symbol), it means there is a break between these two points. The normal resistance of the working winding is usually 10-30 Ohms, and the starting winding is 30-50 Ohms, although the exact numbers depend on the specific model, for example, they may differ. LG And Samsung they may vary.
You need to ring all three pairs of contacts. Record the resulting values. The sum of the resistances between the first and second pairs should be approximately equal to the resistance of the third pair (between the extreme contacts). If you get a value close to zero, this indicates a short circuit of the turns inside the winding. Such a motor will not work and will knock out the circuit breaker in the panel.
| Pair of contacts | Normal resistance | Possible malfunction |
|---|---|---|
| Working winding | 10 – 30 Ohm | Open or short circuit |
| Start winding | 30 - 50 Ohm | Open or short circuit |
| Common - Ground | Infinity (∞) | Breakthrough to the case |
Pay special attention to checking for “breakdown” of the case. Press one multimeter probe to any of the three contacts, and the second to a place on the metal body of the compressor that has been cleared of paint (for example, to a copper tube). The device should show infinite resistance. If you see at least some numbers, it means that the insulation is broken and voltage is reaching the housing. Operating such a refrigerator is deadly.
Why can the readings jump?
If, when measuring resistance, the numbers on the multimeter screen are constantly changing or slowly increasing, this may indicate the presence of moisture inside the windings or the beginning process of insulation degradation. When dry, the resistance should be stable. Also, unstable readings occur when the probes have poor contact with the terminals due to oxides.
Direct connection of the compressor to the network
If the multimeter shows that the windings are intact and there is no breakdown on the housing, but the motor does not start, you can try to start it directly, bypassing the standard relay. This method allows you to check whether the engine is capable of reaching operating mode. To do this you will need to assemble a temporary chain. Important: the starting winding must receive power only briefly, at the moment of start, otherwise it will burn out. Therefore, it is impossible to simply supply 220V to all contacts - you need to simulate the operation of a relay or use a button.
The connection diagram is simple: a phase is supplied to the working terminal, a phase is supplied to the starting terminal through a button (or a short touch), and zero is supplied to the common terminal. At the moment of switching on, you need to press the button that supplies current to the starting winding. As soon as the motor picks up speed (in 1-2 seconds), the button must be released. If the compressor hums but does not start, the piston may be stuck or there is no starting torque.
⚠️ Attention: When connecting directly, do not hold the compressor in your hands! It may vibrate violently or break out due to a jerk when starting. Also remember that there may be high pressure in the system, and a sudden start can cause the tubes to rupture if there are hidden defects.
There is an alternative method using a capacitor, which helps create a phase shift for starting. The capacitance of the capacitor is selected experimentally, but for a one-time test you can do without it if you act quickly. However, if you have a starting device from another refrigerator or a universal relay (RKT, RCO), it is better to use them - it is safer and more reliable for diagnostics.
- ⚡ Use wires with a cross-section of at least 0.75 mm² for connection to avoid heating.
- ⏱️ The time for applying voltage to the starting winding should not exceed 3-4 seconds.
- 🔌 Be sure to use a button or switch, and not twisting the wires, to control the process.
If, when turned on directly, the motor hums, twitches, but the shaft does not spin, and the current consumption increases sharply, then the mechanical part is jammed. In this case, no electrical manipulation will help. If the engine starts and runs smoothly, making a characteristic pumping sound, then the problem was in the old relay, and replacing it will solve the issue.
Analysis of engine sounds and behavior
Sound diagnostics is an important stage that is often ignored. A working compressor emits a uniform, monotonous hum when operating. If you hear a metallic knocking, clanging or grinding noise, this is a sure sign of destruction of the internal mechanical components: the piston group, valves or engine mount. In such cases compressor repair is not economically feasible, a complete replacement is required.
Pay attention to how the motor behaves after starting. If it turns on, runs for a few seconds, and then turns off spontaneously (even with a direct connection), the internal thermal protection may have tripped. This occurs when the windings are severely overheated, which can be caused by an interturn short circuit, which is not always visible when testing with a multimeter in a cold state. Also, the cause may be low voltage in the network or problems with the cooling system of the compressor itself.
A critical sign of a malfunction is the situation when the motor starts, but does not create pressure: the tubes at the outlet and inlet remain the same temperature, and refrigerant circulation does not occur. This indicates that the valves inside the compressor are not working or are destroyed, and it simply circulates gas inside itself without creating a pressure difference.If you observe sparking in the contact area during operation, this indicates poor contact or arcing discharge. If oil vapors are present, this may cause a fire. Stop testing immediately. It is also worth listening to the sound of suction: if a whistle or hissing is heard from the opening of the suction tube, but there is no pressure, the tightness of the compressor crankcase may be broken.
Typical mistakes when checking independently
Beginners often make mistakes that lead to false conclusions or damage to serviceable equipment. One of the most common is an attempt to check the motor without completely disconnecting the relay. In some circuits, the relay may bypass the windings or create an incorrect circuit, causing the multimeter to show incorrect resistance readings. Always carry out diagnostics only on the “bare” contacts of the compressor.
Another mistake is ignoring the condition of the wires. Even if the motor itself is working properly, burnt or oxidized wires can create high contact resistance, which will prevent the motor from starting. As a result, the technician replaces a working compressor, although it would have been enough to clean the contacts or replace the terminals. They also often forget to check the capacitor (if it is in the circuit), which, if it fails, does not provide the required phase shift for starting.
Do not forget about the temperature factor. The winding resistance depends on temperature. A “hot” motor will show more resistance than a “cold” one. If you have just performed start-up tests, allow the unit to cool before re-measuring to ensure correct data. Comparing the readings with factory tables for a specific model, for example Bosch or Whirlpool, will also help to avoid errors.
- ❌ Do not check the resistance by holding the probes with your hands - the body will introduce its own error into the measurements.
- ❌ Do not leave the motor running directly for longer than 5-7 minutes without monitoring pressure and temperature.
- ❌ Do not ignore the smell of burning - even a faint smell of burning insulation requires immediate stoppage of work.
It is important to understand that diagnostics without a relay is only part of the process. Even if the engine starts, this does not guarantee its long operation. A worn-out engine may still work for some time, but its resource has already been exhausted. Therefore, if the refrigerator is more than 10-12 years old, replacing the compressor may be a more reasonable step than resuscitating the old one.
Frequently asked questions (FAQ)
Is it possible to check the compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without instruments. However, performance can be indirectly judged by the sound and response to switching on. If the motor hums and vibrates when connected directly, the windings are most likely intact. If there is silence or traffic jams, there is a problem. But to be sure, a multimeter is needed.
Why does the engine hum, but does not start after checking?
This is a classic sign of a jammed piston group or lack of starting torque. If you have connected the starting winding correctly, but the shaft does not spin, then the mechanical part is faulty. Sometimes briefly applying voltage to the working winding in reverse order helps, but this is a risky method.
Is it dangerous to run a compressor without a relay for a long time?
Yes, it is dangerous. The starting relay turns off the starting winding after the start. If you leave power on it constantly, it will burn out in a matter of minutes. In addition, the relay protects against overloads. Use direct connection only for short-term diagnostics (no more than 10-15 seconds).
How to distinguish the working terminal from the starting terminal without a circuit?
Usually the resistance of the starting winding is higher than the working one. Measure the resistance between the common terminal and the other two. Where the resistance is greater (for example, 40 ohms versus 15 ohms), there is a starting winding. The common terminal is the one with respect to which the sum of the resistances of the other two gives the resistance between them.
Is it worth repairing an old compressor if it is faulty?
Modern hermetic compressors are not designed for repair. Their body is welded at the factory. Opening, rewinding or replacing valves in artisanal conditions is impossible or economically unfeasible. If a winding malfunction or mechanical jamming is confirmed, the unit must only be replaced.