The situation when the refrigerator stops freezing, and there is deathly silence inside or, conversely, a hum is heard without starting, is familiar to many owners of household appliances. Most often, the cause of the breakdown is compressor the heart of the refrigeration unit, which is responsible for the circulation of the refrigerant. Before calling a technician or buying a new device, it makes sense to conduct an initial diagnosis to understand the scale of the problem. Self-checking allows you to weed out simple faults, such as a failed thermostat or start relay, from more serious problems with the motor windings.
It is important to understand that working with electrical components requires compliance with safety rules. Any manipulations with compressor should be carried out only with the device completely disconnected from the network. Incorrect diagnosis can lead to electric shock or permanent failure of an expensive component. In this article, we will analyze in detail the algorithm of actions, the necessary tools and methods that will help you determine whether the motor of your refrigerator is alive.
It is worth noting that modern inverter models may have differences in design and diagnostic methods compared to classic linear units. If you have a refrigerator with No Frost or inverter control, some check steps may differ. However, the basic principles of operation of the electric motor remain unchanged, which allows the use of universal methods of initial inspection and testing of windings.
⚠️ Attention: Before starting any diagnostic work, be sure to remove the refrigerator plug from the socket. Residual voltage in the capacitors can be dangerous, so let the device stand unplugged for at least 15-20 minutes before removing the casing.
Visual inspection and initial diagnosis
The first step is always a thorough visual inspection. Do not rush to grab a multimeter, as external signs can immediately indicate the nature of the malfunction. Inspect the back wall of the refrigerator in the area of the compressor: there are no obvious traces of soot, melted insulation or oily smudges. The presence of black carbon deposits on the tubes or motor housing often indicates an interturn short circuit or overheating caused by operation in emergency mode.
Pay attention to the condition of the starting relay, which is usually mounted on the side or bottom of the compressor. If, when you lightly shake the removed relay, a ringing sound is heard inside, like from a broken glass bottle, then, most likely, its internal “tablet” or posistor has burned out. This is a common reason why the engine hums but does not start. Also check the integrity of the wires going to the terminal box: they should not be frayed or singed.
Pay special attention to the temperature of the compressor housing. If the unit has just been running and is very hot, allow it to cool before checking. A hot motor may have a thermal protection relay that opens the circuit before it cools down. An attempt to start a hot compressor may be useless, since the protection will work again after a few seconds.
Necessary tools for testing
For high-quality diagnostics, you will need a minimum set of tools that most home craftsmen can find. The main device is multimeter (tester), which allows you to measure the resistance of the windings and check for a short circuit to the housing. Without this device, it is almost impossible to accurately diagnose the electrical part.
In addition to the multimeter, you may need:
- 🔧 A set of screwdrivers (phillips and flat) for removing the protective casing and dismantling the relay.
- 🔌 Wires with clips ("crocodiles") for temporary connection of windings.
- 🔨 Hammer (carefully!) for checking shaft jamming by tapping.
- 🧤 Dielectric gloves to protect hands when working with electricity.
If you plan to carry out more in-depth diagnostics, for example, checking pressure or tightness, you will need a pressure gauge station, but for an initial check of the motor at home, a regular tester is sufficient. Make sure that the batteries in the multimeter are charged, since if the battery is dead, the resistance readings may be incorrect, which will lead to false conclusions.
Checking the starting relay and thermal protection
Before sinning on the motor itself, it is necessary to eliminate the malfunction of the starting relay and thermal protection relay. It is these components that most often fail, simulating a compressor breakdown. Remove the plastic casing from the compressor, disconnect the wires and carefully remove the start relay. It can be attached with latches or simply put on the contacts.
The relay is checked with a multimeter in resistance measurement mode. For posistor relays, the resistance should be within normal limits (usually several tens of Ohms), and when heated, it should go to infinity. The thermal relay in a cold state should “ring” (have zero resistance), and when heated, open the circuit. If the relay does not ring or, on the contrary, shows a short circuit, it must be replaced.
⚠️ Attention: The design of the starting relays may vary depending on the brand (Indesit, Bosch, LG). Do not install a relay from another refrigerator model without checking the connection diagram, as this may lead to burnout of the compressor windings.
After checking the relays, if they are working, you can proceed to testing the engine itself. It often happens that replacing a cheap relay brings the refrigerator back to life, and the compressor does not need to be changed. Therefore, do not ignore this diagnostic stage.
How to distinguish a posistor relay from an induction one?
A posistor relay contains a ceramic element (tablet) and usually has one input and two outputs. Induction relays have a coil and a movable core, they are noisier during operation and are often used in older models of refrigerators.
Testing the windings with a multimeter
This is the most important diagnostic stage, allowing you to determine the condition of the electrical windings of the motor. The compressor terminal block usually has three contacts (sometimes four if there is a ground connection). Two of them are responsible for the starting winding, two for the working winding, and one is common. To correctly identify them, refer to the electrical diagram on the relay body or use the resistance measurement method.
Turn the multimeter into resistance (ohms) mode. Measure the resistance between each pair of contacts in turn. You should get three values: the resistance between the work and start windings, the resistance of the start winding and the resistance of the work winding. The sum of the two smaller values must equal the largest value. If you see infinity (1 or OL) in any section, it means there is a break in the winding and the compressor is faulty.
Below is a table with approximate resistance values for a working compressor:
| A pair of contacts | Expected resistance | What does deviation mean |
|---|---|---|
| Working winding | 10–30 Ohm | Infinity - open, 0 Ohm - short circuit |
| Start winding | 20–50 Ohm | Infinity - open, 0 Ohm - short circuit |
| Common - Housing | Infinity | Any value means a breakdown to the housing (dangerous!) |
If the resistance values differ greatly from the table or from each other, this may indicate an interturn short circuit. In this case, the engine will get very hot and hum, but will not be able to work fully. It is also important to check that there is no resistance between any contact and the copper tube or compressor housing ("breakdown" test). If the multimeter shows at least some resistance between the winding and the housing, it is strictly forbidden to use such a compressor - it is mortally dangerous.
☑️ Checklist for checking the windings
Direct connection of the compressor (Piezotest)
If the winding test shows normal results, but the motor does not start through the standard relay, you can try to start it directly. This method, often called a “piezo test” (although the piezo element has nothing to do with it, we are talking about direct starting), allows us to eliminate malfunction of the control system. To do this, use a special starting device or a carefully assembled circuit with a button and a capacitor.
The essence of the method is to apply 220V voltage directly to the working winding and briefly connect the starting winding to create torque. Attention: this method requires extreme caution. Incorrect connection may result in electric shock or explosion of the capacitor. If you are not confident in your skills in working with high voltage, it is better to skip this step.
Action algorithm:
- ⚡ Connect the wires from the 220V plug to the contacts of the working winding (usually the outermost contacts).
- 🔌 In parallel, connect the starting winding through a button or starting device.
- 👆 Briefly press the start button (no more than 1-2 seconds) to give a rotation impulse.
- 👂 Listen to the sound: a smooth hum and vibration of the tubes indicate the serviceability of the mechanics motor.
If, with a direct connection, the motor shaft begins to rotate and a characteristic operating sound is heard, it means that the motor itself is working, and the problem lies in the relay, thermostat or control board. If the motor hums, jerks, but does not start, or knocks out the machine in the shield, most likely there is a mechanical wedge or a serious inter-turn short circuit.
⚠️ Attention: When connected directly, the compressor should not operate for more than 5-10 seconds without a cooling system, as it can quickly overheat. Also make sure that the refrigeration unit is not charged with a flammable refrigerant (for example, isobutane), although the risk of a spark with proper assembly is minimal, caution will not hurt.
Diagnostics of mechanical faults
Electrical serviceability is only half the battle. A compressor may have intact windings but be completely inoperable due to mechanical problems. The most common of them is wedge piston group. This happens when, due to depletion, contamination of the system or solidification of the oil, the piston gets stuck in the cylinder and cannot perform reciprocating movements.
You can determine the wedge by the characteristic hum when you try to start and the absence of vibration on the tubes. Sometimes the “wedging” method helps: gently tapping the compressor body with a wooden or rubber mallet at the moment the voltage is applied. In some cases, this helps to move the piston out of place. You can also try heating the bottom of the compressor (where the oil is) with a heat gun to reduce the viscosity of the oil, but this method does not always work.
Another mechanical problem is a broken connecting rod or valves inside the housing. In this case, the motor may work, but not create the necessary pressure. You can check this by disconnecting the compressor outlet tube and checking the strength of the air being blown out with your finger (be careful, oil may be blowing out!). If the blowing is weak or absent at all, and the motor is humming, the compressor requires replacement.
Is it possible to restore a jammed compressor?
In rare cases, long-term (several hours) operation under high voltage or adding a special flushing fluid to the system helps, but these are temporary measures. It is more reliable and safer to replace the unit.
Frequently asked questions and answers (FAQ)
Is it possible to check the compressor without a multimeter?
It is impossible to fully check the condition of the windings without instruments. However, you can visually assess the integrity of the wires and try to start the motor directly through a working starting relay. If the motor hums and vibrates, it is probably alive. But this will not guarantee the absence of breakdown on the housing.
Why does the compressor hum but does not start?
Most often the reason is a faulty starting relay (the posistor has burned out or the core has jammed), a break in the starting winding or a mechanical wedge of the piston group. It is also possible that the voltage in the network may drop below the permissible level.
Which compressor is better: piston or inverter?
Inverter compressors (Linear Inverter) are quieter, more economical and more durable, but their diagnosis and replacement are more difficult and more expensive. Piston compressors are easier to repair and cheaper, but they are noisier and have more moving parts that are subject to wear.
How much does it cost to replace a compressor?
The cost consists of the price of a new unit (from 3 to 10 thousand rubles, depending on the model) and the cost of the work of a specialist. In total, replacement often amounts to 50–70% of the cost of a new refrigerator, so sometimes it is more advisable to buy new equipment.
Is it dangerous to change the compressor yourself?
Yes, it is dangerous. The process requires soldering tubes, working with gas under pressure and evacuating the system. Incorrect soldering or refrigerant quantity may result in an explosion, fire, or rapid failure of the new compressor. It is better to entrust this part of the work to professionals.