The situation when the refrigerator stops cooling, but there is silence inside or, conversely, a hum is heard without starting, often confuses the owner. In most cases, the cause of the failure is compressor electric motorwhich is the heart of the entire refrigeration system. Understanding how to properly diagnose this unit can save you from an expensive call to a technician or, conversely, confirm the need for professional intervention.
Before you grab the tools, it is important to realize that checking the motor is not just checking the wires, but a set of measures to identify mechanical and electrical defects. The fault may lie in the windings, start relay, capacitor, or even in a jammed piston mechanism. We will analyze all stages of testing from visual inspection to accurate resistance measurements.
In this article we will consider in detail the algorithm of actions that will allow you to determine the condition with a high degree of probability compressor. You will learn to distinguish a burnt winding from an interturn short circuit and understand when repairs no longer make sense. Remember that working with electricity and refrigerants requires caution and safety precautions.
Primary diagnostics and visual inspection
Any diagnostics begins long before you pick up a multimeter. The first step should always be to take a good look at the back of the refrigerator. Often external signs can point to a problem faster than complex measurements. Pay attention to the condition of the compressor: are there any traces of oil on its body, which may indicate depressurization of the system. visual inspection the back of the refrigerator. Often external signs can point to a problem faster than complex measurements. Pay attention to the condition of the compressor: are there any traces of oil on its housing, which may indicate depressurization of the system.
If the refrigerator hums but does not start, or, conversely, is completely silent, listen to the nature of the sounds. Relay clicks, intermittent buzzing, or a complete lack of response to being plugged into the network are all important symptoms. Also check the integrity of the supply wires and the condition of the terminal block.
⚠️ Attention: Before starting any diagnostic work, be sure to disconnect the refrigerator from the electrical network! Working under voltage is fatal and may result in electric shock.
Inspect the start relay and protective device, which are usually attached to the compressor housing. There should be no traces of burning, melted plastic or the characteristic smell of burnt insulation. If you see black marks on the contacts, this is a sure sign that starting relay requires replacement or inspection.
Sometimes the problem lies not in the motor itself, but in the heat dissipation system. Check the condenser (grid at the back), it should be warm, but not hot. If the grille is cold and the motor is trying to start, there may be a blockage in the capillary tube or a freon leak, which creates excess pressure that prevents the piston from moving.
Checking the starting relay and protective device
Before testing the electric motor itself, it is necessary to rule out a malfunction of its “retinue”. The starting relay is responsible for briefly supplying voltage to the starting winding, and the thermal relay protects the motor from current overloads. Often it is these cheap components that fail, creating the illusion of a breakdown of an expensive compressor.
Remove the relay from the compressor, having first photographed the wiring diagram. Shake the device next to your ear: if a ringing sound is heard inside, it means that the contact group or the hammer relay mechanism is damaged. For electromagnetic relays, visual inspection of the contacts for oxidation is important.
The thermal relay is checked for the integrity of the bimetallic plate. If it is deformed from overheating, the circuit will not close. Also check the contacts for the presence of carbon deposits, which creates a high contact resistance and prevents the motor from receiving the necessary current to start.
How to test a relay with a multimeter?
To check the relay, use the dialing mode. Normally closed contacts should ring (resistance close to 0 ohms). Open contacts should show infinity. When voltage is applied (carefully!) to the coil, the relay should click, changing the state of the contacts.
If, after replacing the relay with a known good one (you can take it from another compressor of the same series), the situation has not changed, proceed to directly checking the motor windings. This is the next and most important stage of diagnosis.
Technology for testing windings with a multimeter
For accurate diagnostics, you will need a digital multimeter. Switch the device to resistance measurement mode (Ohms), selecting a limit of 200 Ohms or 2 kOhms. On the compressor body you will find three terminals, often covered with a plastic cap. Remove the cover and determine the location of the contacts.
Usually the terminals are marked with letters or arranged in a certain order (triangle). You need to find pairs of windings: starting, working and common point. The resistance between the common point and the working winding should be the smallest, and between the common point and the starting winding it should be about 1.5 times greater. The sum of these two resistances should be equal to the resistance between the starting and working terminals.
During the measurement process, pay attention to the instrument readings. If the multimeter shows one (infinity) on any of the pairs, this means winding break. In this case, the electric motor cannot be repaired and requires replacement. If the resistance is close to zero, this indicates a short circuit of the turns.
☑️ Algorithm for checking the compressor
Pay special attention to the check for insulation breakdown. Press one multimeter probe to the cleaned area on the compressor body (where there is no paint), and with the other touch all three terminals one by one. With proper insulation, the device should show infinity. Any resistance value indicates that the insulation is broken and the motor “breaks through” the housing, which is life-threatening.
Table of normal resistance values
For ease of comparison of the data you received, we will give approximate resistance values for household compressors. Remember that specific numbers may differ depending on the engine power and manufacturer (Atlant, Danfoss, Secop), but the proportions must be maintained.
| Pair of contacts | Winding type | Normal resistance (Ohm) | Possible malfunction |
|---|---|---|---|
| Working - General | Main | 10 - 30 Ohm | Open or short circuit of turns |
| Starting - General | Starting | 20 - 50 Ohm | Open or short circuit of turns |
| Starting - Working | Total | 30 – 80 Ohm | Circuit failure |
| Any output - Housing | Isolation | Infinity (∞) | Fault to ground |
If your measurements differ radically from the table ones, for example, the resistances are equal or absent, this is a sure sign of an internal malfunction. It is also worth noting that the resistance of the windings may vary slightly depending on the temperature of the engine (whether it is cold or warm).
Mechanical check and direct connection test
If the electrical part is in order (the windings are intact, there is no breakdown to the housing), but the compressor does not start, it may be mechanically jammed. This often happens after a long period of inactivity or when working under extreme conditions. You can check this by trying to start directly, bypassing the standard relay.
To do this, use a special start button or a circuit with a capacitor. Attention: This method requires caution and skills in working with 220V electricity. You need to apply voltage briefly (for 1-2 seconds). If the motor hums, jerks, but does not turn, and the shaft does not turn manually (on some models there is access to the shaft), then the piston group is jammed.
⚠️ Attention: When directly connected, do not keep the compressor running for more than a few seconds without the cooling system connected! This can lead to rapid overheating and final failure of the unit.
There is a “wedging” method by applying increased voltage or vibration, but at home it rarely gives long-term results. If the compressor is jammed, its resource is usually exhausted. Attempts to revive such a unit often lead to repeated breakdown after a short time.
Sometimes the cause of a mechanical stop is the lack of oil or its coking. If you hear a strong metallic knock when you try to start, this is a bad sign - the liners or piston group are destroyed. In this case, further operation is impossible.
Analysis of current consumption and interturn short circuit
The most difficult fault to diagnose is an interturn short circuit. With it, the winding is intact, the resistance is normal, there is no breakdown to the housing, but the engine does not work correctly, gets hot and knocks out the circuit breaker. It is almost impossible to detect this with a conventional multimeter, since the change in the resistance of several turns is negligible.
For accurate diagnosis in this case, current clampsare necessary. Connect them to the compressor power cable at startup. The starting current of a working engine briefly increases to 10-15 Amperes, and a working one is 0.5-1.5 Amperes (depending on power). If the current is significantly higher than the rated current indicated on the nameplate, then there is a short circuit in the winding.
An indirect sign of an interturn short circuit can be the rapid and strong heating of the compressor housing even when operating at idle speed (without freon and load). This is also indicated by the knocking out of the circuit breaker in the apartment's electrical panel precisely at the moment the refrigerator is operating.
Repairing a motor with an interturn short circuit in domestic conditions is impractical. Rewinding windings requires special equipment and knowledge, and the cost of such work is often close to the price of a new compressor. In such cases, a complete replacement of the unit is recommended.
Frequently asked questions and final recommendations
To summarize, we can say that diagnosing a refrigerator electric motor is a logical and consistent process. You should always start with something simple: checking the voltage in the network and the integrity of the wires. This is followed by a visual inspection and check of the starting fittings, and only then - a deep diagnosis of the motor itself.
Do not forget that a modern refrigerator is a complex device. Even if the motor is working properly, the lack of cold may be caused by a refrigerant leak or a clogged system. Therefore, if the electrical part of the compressor is ideal, but there is no cold, the problem lies in the sealed circuit.
It is important to remember safety. The refrigerant in the system may be flammable (isobutane) or under high pressure. Do not open copper tubes and do not try to refuel the refrigerator yourself without the appropriate equipment and knowledge.
Is it possible to replace the compressor with another, non-original one?
Yes, you can often install an analogue, but a number of conditions must be met: the power of the new engine must be equal to or slightly higher than the original, the mounting dimensions of the feet must match, and the diameter of the tubes must match. It is also important to use the correct oil and freon for which the new compressor is designed.
Why did the new compressor immediately burn out after installation?
A common reason is poor-quality evacuation of the system or moisture ingress. Also, the compressor may burn out due to a faulty start relay, which was forgotten to be replaced along with the motor, or due to a blockage in the system that creates excess pressure.
How long does a refrigerator electric motor last on average?
The average service life of a modern compressor is 10-15 years. However, with intensive use, frequent defrosting or power surges in the network, this period can be reduced to 5-7 years.
Is it dangerous to touch a running compressor?
Yes, it is dangerous. The housing of a working compressor heats up to 70-90 degrees Celsius and higher, which can cause burns. In addition, there is a risk of electric shock if the insulation is broken or the wires are handled carelessly.