When your refrigerator suddenly stops cooling, and the food inside quickly deteriorates, The first thought is often to call the master. However, in most cases, primary diagnostics can be carried out independently, without having in-depth knowledge of electronics. The key unit that ensures the circulation of the refrigerant is motor-compressor, and it is its condition that determines the performance of the entire cooling system.
Before proceeding with disassembly or complex measurements, it is necessary to exclude trivial reasons: check whether the light inside is on, whether the door is tightly closed and whether the power cord has come loose from the outlet. If an external inspection does not produce results, and the unit hums, but does not freeze, or is completely silent, while there is light inside, then it’s time to check the electrical circuit the engine.
In this article we will analyze in detail the algorithm of actions that will help you determine whether the compressor is alive or the problem lies in the starting relay. The normal resistance of the windings of a working motor is usually from 20 to 40 Ohms for the starting winding and from 10 to 25 Ohms for the working winding, but the exact values depend on the specific model. Remember that any work with electrical appliances requires strict adherence to safety precautions.
⚠️ Attention: Before starting any diagnostic work, be sure to disconnect the refrigerator from the power supply! Unplug the plug from the socket. Working with live electricity is deadly, and capacitors in the circuit can retain a charge even after being switched off.
Visual inspection and initial diagnostics
The first step is always a visual assessment of the condition of the equipment. You need to gain access to the lower back of the refrigerator where the compressor unit is located. Remove the protective panel (if there is one) and inspect the motor for obvious mechanical damage, traces of oil or burning.
Pay attention to the wires going to the compressor. They should not have melted insulation or cracks. Often the cause of failure is overheating, which can be seen by blackening of the relay housing or swelling of the capacitor. If you see traces of oil leakage, this may indicate mechanical damage to the compressor itself or a leak in the system.
Also listen to the sounds that the unit makes when turned on. A dull hum, turning into a click and silence, indicates an attempt to start. If a cracking sound is heard or the humming suddenly stops, this is a sure sign of a malfunction in the electrical part or mechanical jamming.
For more accurate diagnostics, you will need a basic set of tools. Do not try to disassemble the assembly without preparation, as you can damage the fragile contacts.
- 🔧 Multimeter (tester) - the main device for measuring resistance and checking the circuit for open circuits.
- 🔧 Screwdrivers (flat and cross) - for removing protective covers and dismantling the relay.
- 🔧 Pliers —may be needed to carefully remove the terminals.
- 🔧 Flashlight —for illuminating hard-to-reach places in the rear niche of the refrigerator.
Removing the starting relay and accessing the contacts
To ring the motor windings, you need to gain direct access to the contact group. On the compressor housing, in its upper part, there is a black plastic or metal box - this is the starting relay. It is this that gives the impulse to start the engine.
Remove the relay carefully by pulling it down or snapping off the retaining clips, depending on the design. On some models, such as Indesit or Atlant, the relay can be mounted on a bracket. Do not use excessive force to avoid breaking the plastic tabs.
After removing the relay, you will see three contacts coming out of the compressor housing. They are arranged in a triangle. They usually have markings, but if they are missing or worn off, it is important to identify them correctly. In the upper part of the triangle there is always a common contact (C), and in the lower corners there are starting (S) and working (R) windings.
How to identify contacts without markings?
Place the triangle of contacts with the apex up. The top pin is the common wire. The lower left is the starting winding (Start), the lower right is the working winding (Run). This is a standard scheme for most compressors.
Before measuring resistance, clean the contacts from oxides and dust. Use a dry cloth or compressed air. An oxidized contact may give false readings, and you will mistakenly decide that the engine has burned out.
⚠️ Attention: In older models of refrigerators, there may be a mercury switch inside the relay. Be extremely careful when dismantling it, do not break the case and do not allow mercury to come into contact with your skin or the environment. Dispose of such parts at special collection points.
Checking the motor windings with a multimeter
The most reliable way to check the condition of the electric motor is to measure the resistance of its windings. Switch the multimeter to resistance measurement mode (Ohms, symbol Ω) to the 200 Ohm or 2 kOhm limit. This will allow you to obtain accurate data without errors.
Attach the tester probes to the contacts. First measure the resistance between the top contact and the bottom left, then between the top and bottom right. The results must fit within a certain framework. If the device shows infinity (one on the left on the screen), it means that the winding is damaged break, and the engine cannot be repaired.
Below is a table with approximate resistance values for a working compressor. Remember that the data may vary slightly depending on the manufacturer and motor power.
| Pair of contacts | Winding type | Normal resistance (Ohm) | Fault symptom |
|---|---|---|---|
| General - Working (C-R). data-i="100">20 - 40 Ohm | Working winding | 10 – 25 Ohm | Open circuit or short circuit |
| General - Launcher (C-S) | Start winding | 20 – 40 Ohm | Open or short circuit |
| Working - Starting (R-S) | Total | Sum of the previous two | Inconsistency with the amount |
| Any contact - Housing | Failure to ground | Infinity (∞) | Any value (short circuit) |
Pay special attention to checking for insulation breakdown. Press one probe to any of the three contacts, and the second to a cleaned area on the metal body of the compressor (for example, to a copper tube). The device should show infinity. If you see any numbers, it means that something has happened short circuit on the housing, which makes operation of the unit dangerous.
☑️ Multimeter testing algorithm
Diagnostics of the starting relay and thermal relay
Often the electric motor itself is fine, but the problem lies in start relay. This device is responsible for briefly supplying voltage to the starting winding. Inside the relay there is an inductor and contacts that can burn or stick over time.
Shake the relay near your ear. If you hear a rattling sound similar to the clinking of coins, it means that the internal contacts are damaged or the mechanism is jammed. This relay requires replacement. Also check the condition of the thermal relay (protective device), which opens the circuit when overheated.
Test the relay contacts with a multimeter. In normal condition, they should ring (show zero or close to zero resistance). If the circuit is broken, the relay does not pass current to the engine, and the compressor will not start, even if its windings are intact.
Some modern models use solid state PTC relay. They have no moving parts and are tested only for resistance. If it differs from the nominal value or is equal to zero/infinity, the part is replaced entirely.
Mechanical malfunctions and jamming
There are cases when the electrical part of the engine is fully operational: the windings are intact, there is no breakdown to the body, the relay is working, but The compressor does not start or hums and immediately turns off. This may indicate mechanical jamming of the piston group.
The cause of jamming is often a lack of oil or moisture entering the system, which leads to corrosion and the formation of scoring on the cylinders. In this case, the motor shaft cannot turn, and the starting current increases sharply, causing the protection to trip.
There is a “wedging” method by applying increased voltage, but it is extremely dangerous and requires special equipment (transformer). Use this method at home not recommendedas you can completely kill the compressor or get an electric shock.
- 🔨 Knock with a hammer: Sometimes a light blow with a rubber mallet on the compressor body can dislodge a jammed piston. Do this only when the power is turned off!
- 🔨 Heating: Heating the compressor housing with a hair dryer can expand the metal and free jammed parts, but the effect is often temporary.
- 🔨 Replacement: If mechanical jamming confirmed, the most reasonable solution would be to replace the compressor unit.
⚠️ Attention: It is strictly forbidden to open the sealed compressor casing (cut off the “pot”) at home. There is oil under pressure inside, and freon can be flammable. In addition, after opening, the tightness is broken, and the compressor becomes unsuitable for operation without expensive refilling.
Replacing the compressor: is it worth the candle?
If diagnostics showed that the electric motor is burnt out (interturn short circuit, break, breakdown on the body) or jammed, the question of repair arises. Replacing a compressor is a complex technical process that requires a vacuum pump, a pressure gauge station and a supply of freon.
The cost of a new compressor along with the work to replace it, including refrigerant charging, can be up to 60-70% of the price of a new refrigerator. Therefore, if your unit is more than 10 years old, it makes more economic sense to purchase new equipment.
However, if the refrigerator is premium or has other unique characteristics, replacing the motor may be justified. It is important to choose an analogue with the same parameters: power, refrigerant, volume and type of oil.
When installing a new engine, be sure to replace the filter drier. An old filter may contain moisture, which will quickly damage a new compressor. Also check the condition of the condenser (radiator at the back) - it should be clean and free of dents.
Is it possible to check the compressor without a multimeter?
Theoretically, you can apply 220V voltage directly, bypassing the relay, but this is very dangerous. You may receive an electric shock or cause a fire if the motor is short-circuited. In addition, this method will not provide accurate information about the state of the windings, but will only show whether the shaft is spinning or not. Using a tester is the only safe and informative way.
Why does it hum, but does not start?
The hum means that current is supplied to the working winding, and a magnetic field is created, but the rotor cannot turn. Reasons: jamming of the mechanical part, malfunction of the starting relay (does not supply a pulse to the starting winding) or low voltage in the network.
What is an interturn short circuit?
This is damage to the insulation between the turns of copper wire inside the winding. At the same time, the resistance drops, the current increases, the engine heats up and hums. A multimeter may show normal resistance, but during operation such an engine will get very hot and knock out the circuit breaker. This is most accurately diagnosed with special devices, but an indirect sign is strong heating and humming.
Is it possible to use a compressor from another refrigerator?
It is possible if the technical characteristics match: type of refrigerant (R134a, R600a), power, overall dimensions and mounting holes. It is also important to take into account the type of oil, since different refrigerants require different oils, and mixing them is unacceptable.