A sudden stop in the operation of the refrigeration chamber or, conversely, its continuous hum often indicates problems with the heart of the unit - the compressor. It is this unit that is responsible for circulating the refrigerant, creating the necessary pressure in the system. If you notice that the food has begun to deteriorate, and the motor hums but does not start, or turns on only for a couple of seconds and immediately turns off, it’s time to carry out diagnostics.
Before calling a technician or buying new equipment, you should try to find out the cause of the breakdown yourself. Compressor diagnostics does not always require complex equipment, although a basic set of tools is still necessary. In most cases, the problem lies in the starting relay, a broken winding or an interturn short circuit, which can be identified visually or using a multimeter.
In this article we will analyze in detail the algorithm of actions that will help you understand whether the motor is alive or its replacement is inevitable. You will learn how to safely get to the unit, what sounds to pay attention to and how to use measuring instruments correctly. A competent check will save you money and time, allowing you to make an informed decision about repairs.
⚠️ Attention: Carry out all work on diagnosing the electrical components of the refrigerator only after a complete disconnect the device from the power supply! Residual voltage in capacitors can be dangerous.
Visual inspection and initial diagnosis
The first step is always an external inspection. The compressor is located at the bottom rear of the refrigerator, often covered by a casing. After removing the protective panel, you will see a black metal tank - this is the motor-compressor. Pay attention to its appearance: there should be no traces of oil, severe corrosion or melting.
If oil stains are visible on the tubes or housing, this is a sure sign of depressurization of the system. Freon leak often accompanied by loss of oil, which circulates along with the refrigerant. In this case, even an electrically serviceable motor will not be able to start due to the protection being activated or lack of lubrication of the rubbing parts.
Listen to the sounds when you try to turn it on. If there is a quiet click, followed by a buzzing sound that lasts 5-10 seconds, and then a stop click, this is a classic symptom. This situation may indicate jamming of the piston group or failure of the start relay. Sometimes a light blow to the compressor housing (not too strong!) helps to dislodge the jammed piston, but this is a temporary measure.
Also inspect the wires going to the terminal box. They must be intact, without traces of melted insulation. If the plastic turns black, it means that there was overheating in the circuit caused by poor contact or short circuit. Melted contacts require stripping or replacing the terminals before further testing.
Required tools for testing
For high-quality diagnostics you will need a minimum set of tools. Without them, it is almost impossible to check the integrity of the windings and the presence of a breakdown in the housing. The main device will be a multimeter (tester) configured to measure resistance (Ohm) and circuit integrity.
- 🔧 Multimeter - the main device for measuring winding resistance and checking for breakdown.
- 🔧 Screwdrivers (cross and flat) - for removing the casing and dismantling the terminal block boxes.
- 🔧 Pliers —may be needed to carefully remove the terminals.
- 🔧 Sandpaper —for cleaning contacts if they are oxidized.
It is important that the multimeter probes are in good working order, and that the device itself shows zero when the probes are shorted to each other. If you are using a pointer tester (analog), be sure to calibrate it before starting work. Digital multimeters are more convenient in this regard, as they show the exact resistance value.
Also prepare the workplace. It is better to move the refrigerator to the middle of the kitchen or provide access to the back wall from all sides. Good lighting in the compressor area is critical, as the terminals are often located in hard-to-reach places and are painted black.
Removal and access to the electrical part
To get to the contacts, you must remove the start-up relay. It is attached directly to the compressor terminals on the right or left side (depending on the model). First, carefully remove the plastic casing covering the back of the unit.
On the compressor body you will see three terminals covered by a terminal block. The relay usually fits directly onto these pins. Proceed with caution: plastic parts become brittle over time. If the relay is stuck, you can slightly rock it from side to side, but without excessive force.
⚠️ Attention: Before removing the relay, take a photo of the connection diagram or sketch the location of the wires. By mixing up the contacts during assembly, you can instantly burn out the new compressor or relay.
After removing the relay, three metal pins will open in front of you, forming a triangle. These are the winding terminals. Their arrangement is standard for most models: two pins are closer to each other (working and starting windings), and the third, single, is common. However, for different manufacturers, such as Indesit, Atlant or Liebherr, the markings may differ.
Marking of compressor terminals
Usually the terminals are designated by letters: C (Common) - common, R (Run) - working, S (Start) - starting. Some models use numbers or color marks on the terminal block instead of letters.
If carbon deposits or oxidation are visible on the terminals, carefully sand them with fine sandpaper to a metallic shine. This will ensure reliable contact during dialing and subsequent operation. Dirty contacts are a common cause of false multimeter readings.
Checking the windings with a multimeter
The most reliable way to determine the condition of the motor is to ring its windings. Switch the multimeter to resistance measurement mode (limit 2 kOhm or 20 kOhm). First, let's check the integrity of the windings, and then the absence of a breakdown on the case.
Insert the probes into the tester sockets and touch the pairs of terminals with them. You need to get three resistance values: between common and working, between common and starting, and also between working and starting. Normal indicators vary, but are usually:
- ⚡ Resistance between common and working terminal: from 15 to 40 Ohms.
- ⚡ Resistance between common and starting terminal: from 30 to 100 Ohms (the starting winding is thinner, so the resistance is higher).
- ⚡ Resistance between working and starting: the sum of the two previous values.
If the device shows one (infinity) in any of the sections, it means that there is an accident in the winding break. Such a compressor cannot be repaired and requires replacement. If the resistance is close to zero, this indicates an interturn short circuit, which is also a fatal malfunction.
Pay special attention to checking for breakdown of the mass. Press one multimeter probe to any cleaned place on the compressor body (where there is no paint), and with the second touch all three terminals in turn. The device should show infinity. Any resistance value indicates that the winding is shorted to the housing, which is life-threatening and requires immediate replacement of the unit.
For ease of comparison, we provide approximate data for popular models:
| Winding type | Normal resistance (Ohm) | Fault symptom |
|---|---|---|
| Working (Main) | 15 - 35 Ohm | Open (∞) or short circuit (0) |
| Starting | 30 - 90 Ohm | Significantly higher than normal |
| Between terminals | Sum R1 + R2 | Inconsistency with the sum |
| On body | ∞ (Infinity) | Any numeric value |
Diagnostics without instruments and checking relays
What to do if you don’t have a multimeter at hand? There is an indirect verification method based on the exclusion of other faults. First of all, you should check the starting relay, since it is the one that most often fails, simulating a compressor breakdown.
The relay is a plastic box with contacts and a coil. There is a movable core inside. If you hear a rattling sound when you shake the relay, it means the mechanism is damaged. Also, the contacts inside could have burned out. Visually this can be seen by the black soot. Replacing the relay is an inexpensive procedure that often revives the refrigerator.
Another method is to check the startup directly (only for experienced ones!). If you apply 220V voltage directly to the working winding, a working compressor should start confidently. However, this method is dangerous and requires the use of a button to briefly turn on the starting winding. Without special skills, it is better not to take risks.
☑️ Checklist for checking the relay
If the relay is working properly, but the engine hums and does not start, the piston group may be jammed. In this case, the compressor requires replacement, since opening its housing at home is impossible due to the need to evacuate the system and refill with freon.
Analysis of current consumption and temperature
If the compressor starts, but the refrigerator does not freeze, it is worth measuring the current consumption. For this purpose, current clamps are used. The normal operating current of a household compressor is from 0.5 to 1.5 Amperes (depending on the power of the model). If the current is significantly higher than the rating indicated on the tag, this indicates a heavy stroke of the piston or a turn short circuit.
Also pay attention to the temperature of the housing of the running motor. It should be hot (up to 90°C), but not red-hot. If the hand does not tolerate touch for more than a second, the ventilation may be impaired or the motor is operating in overload mode. Thermal relay in such a situation the unit should be turned off, but if this does not happen, the risk of fire increases.
⚠️ Attention: Technical characteristics of compressors may vary depending on the manufacturer and year of manufacture. Always check the rated current and resistance values with the data on the manufacturer's label attached to the motor housing.
Continuous operation at maximum currents quickly damages the equipment. If you notice that the refrigerator begins to work longer than usual or turns on more often, this is a reason to carry out diagnostics sooner rather than later. Ignoring these signs can lead to complete failure of the system.
Frequently asked questions (FAQ)
Is it possible to repair a burnt-out compressor yourself?
No, the compressor is a sealed unit. Its repair requires opening the housing, replacing the valves, piston group and subsequent professional sealing, evacuation and refrigerant charging. This cannot be done at home; the entire unit must be replaced.
Why does the compressor hum but does not start?
Most often the reason is a faulty start relay or a jammed piston group. It is also possible that there may be a voltage drop in the network or contact oxidation. Less commonly, the problem lies in the interturn short circuit of the windings.
What is the service life of a refrigerator compressor?
The average service life of modern compressors is 10-15 years. However, inverter models that operate without constant switching on and off can last up to 20 years or more, subject to operating conditions.
Is it worth changing the compressor on an old refrigerator?
It depends on the cost of the new unit and the work of the technician. If the refrigerator is more than 10-12 years old, replacing the compressor can cost 60-70% of the cost of new equipment. In such cases, it is often more profitable to purchase a new unit with a guarantee and a modern energy efficiency class.