A sudden stop of the refrigerator is always stressful, because food supplies are at risk. Often the cause of a breakdown is a failure compressor, which is the “heart” of the unit. Before calling a technician or buying a new unit, experienced technicians advise conducting initial diagnostics of the electric motor. This will help you understand whether it’s worth the trouble or whether it’s easier to purchase new equipment.
To check the serviceability of the windings, you will need a regular household one. multimeter. This device allows you to measure the resistance of a circuit and detect the presence of an open or short circuit. The verification procedure is relatively simple, but requires strict adherence to safety precautions and sequence of actions. In this article we will look in detail at how to properly prepare the refrigerator, remove the start-up relay and take measurements.
Safety measures and tool preparation
Any work related to electrical components requires maximum caution. The first step is to fully de-energize the refrigerator by removing the plug from the socket. Do not rely solely on the switch if there is one, physically disconnecting from the network is a must. You should also let the unit stand unplugged for at least 15-20 minutes so that the capacitors discharge and the pressure in the system stabilizes.
To carry out diagnostics, you will need a minimum set of tools. The main device will be a multimeter configured to measure resistance (Ohm). Additionally, you will need screwdrivers to remove the casing and, possibly, pliers to carefully remove the terminals. If you plan to start the motor outside the refrigerator, you will need a special starting button or circuit with a capacitor, but this is not necessary for initial testing.
⚠️ Attention: Never touch live parts with wet hands and do not take measurements in a room with high humidity. Residual voltage in the circuit can be life-threatening, even if the refrigerator is unplugged.
Prepare the workplace: it should be well lit and spacious. You will have to lean towards the bottom of the refrigerator, so make sure there is nothing blocking access to the compressor. Wipe the motor area with a dry cloth in advance to remove dust and cobwebs that may make it difficult to visually inspect the contacts.
Accessing the compressor and removing the relay
The compressor in modern refrigerators is usually located in the lower rear part of the case. To get to it, you need to remove the protective casing, which is secured with latches or screws. After removing the metal or plastic panel, you will see a black cylindrical or pear-shaped tank - this is the motor-compressor. A plastic box is attached to its end, inside which there is start-up protection relay a thermal fuse.
The next stage is dismantling the relay. It can be mounted on a clamp bracket or simply slipped onto the three contact studs of the compressor. Carefully remove the retaining bracket (if there is one) and pull the relay down. Be careful not to pull sharply to avoid damaging the wires. On the inside of the relay cover you will see a connection diagram, which it is advisable to photograph on your phone in case you forget the assembly order.
After removing the relay, you will see three studs coming out of the compressor housing. They are arranged in a triangle. Two of them are closer to each other (these are the winding terminals), and the third stands slightly to the side (the common terminal). Before touching them with the multimeter probes, it is necessary to clean the contacts from possible oxide or carbon deposits.
Why might the relay be faulty?
Often the compressor itself is working, and the problem lies in sticking relay contacts or a burnt thermocouple. If the motor continuity test shows normal, but it does not start, replace the start-up relay with a new one.
Searching for the common wire and marking the terminals
Before starting to measure resistance, it is necessary to identify the terminals of the windings. On older models of refrigerators, the studs may be marked: S (Start - starting), R (Run - working) and C (Common - general). However, on many modern units there are no markings, and the master has to determine the purpose of the contacts empirically or by their location.
There is a simple rule for the geometry of the terminals. If you look at the triangle of contacts so that one vertex is on top and two below, then:
- 🔹 The upper contact (often one or located separately) is the common output (C).
- 🔹 The lower left contact is the starting winding (S).
- 🔹 The lower right contact is the working winding (R).
However, you cannot rely only on geometry, since the location may differ among different manufacturers (Indesit, Atlant, Bosch). A more reliable method is “diagnosis” in pairs.
Turn the multimeter into resistance measurement mode (limit 2 kOhm). Call all three pairs of contacts. The resistance between the two terminals will be the greatest - this is the sum of the resistances of the starting and operating windings. The third contact, which did not participate in this measurement (or participated in measurements with lower values), will be common. It is from this that measurements are taken to the other two terminals.
Measuring winding resistance with a multimeter
After you have found the common wire, you can proceed to the main measurements. You need to measure the resistance between the common terminal and each of the other two. In a working engine, the working winding always has less resistance than the starting winding, since it is wound with a thicker wire and contains more turns.
Normal resistance values depend on the power of the motor and the model of the refrigerator, but usually they are within the following limits:
- ⚡ Working winding resistance: from 10 to 35 Ohm.
- ⚡ Starting winding resistance: from 20 to 60 Ohms.
- ⚡ Total resistance (between starting and operating): from 30 to 90 Ohms.
If your measurements fall within these ranges and the difference between the readings is logical (the working part is less than the starting part), then the electrical part of the motor is most likely intact.
It is also important to check that there is no short circuit to the housing. Switch the multimeter to dial mode (with a beep) or to the maximum resistance limit (2 MOhm or higher). With one probe, touch any contact on the compressor, and with the other, touch a cleaned area on the metal motor housing (where there is no paint). The device should be silent, and infinity should be displayed on the screen (number 1 on the left or the OL symbol).
For clarity, we provide a table of typical faults and device readings:
| Fault type | Indications between windings | Indications on body | Verdict |
|---|---|---|---|
| Normal | 10-90 Ohm (different for each pair) | Infinity | Motor OK |
| Open windings | Infinity (OL) | Infinity | Replacement required |
| Interturn short circuit | Significantly below normal (1-5 Ohm) | Infinity | Motor is heating up, replacement |
| Breakthrough to housing | Any values | Zero or small number | Danger! Replacement |
If the multimeter shows zero between any two contacts, this means a short circuit in the turns. Such a motor will not work, and when you try to turn it on, the machine in the panel will immediately knock out or the wiring will burn out.
Diagnostics of thermal relays and additional circuits
Sometimes the problem lies not in the motor itself, but in the attached equipment. The start-up protection relay often has a built-in thermocouple (thermal protection relay), which opens the circuit when overheated. She also needs to be called. In a cold state, it should ring short (resistance is close to zero).
Remove the thermocouple from the relay (it looks like a copper tablet or spiral with contacts). Connect the multimeter probes to its terminals. If the device shows infinity, it means that the thermal protection has burned out or is constantly open. In this case, the compressor will not start, even if its windings are intact. Replacing a thermocouple is a cheap and quick procedure.
⚠️ Attention: Do not try to repair a thermal relay by gluing or permanently shorting the contacts. This will lead to the combustion of the compressor windings at the first overload, since the protection will not work.
Also inspect the wires going from the connector to the relay. Often due to vibration they break at the very entrance to the plastic case. Ring each wire separately, bending it where it leaves the insulation. If the resistance fluctuates or disappears, the wire needs to be replaced or restored.
Possible causes of malfunctions and their symptoms
Understanding why the motor burned out will help avoid a repeat of the situation. Most often, a break or interturn short circuit occurs due to prolonged operation in abnormal mode. For example, if there is not enough refrigerant in the system or circulation is disrupted, the compressor runs non-stop, trying to gain temperature. This leads to overheating and destruction of the winding insulation.
Another common reason is power surges in the network. Although the relay has protection, powerful impulses can break through the insulation. Frequently turning the refrigerator on and off also has a negative effect. If you have just turned off the unit, wait at least 10-15 minutes before turning it back on so that the pressure in the system equalizes.
Symptoms of a faulty motor that can be noticed without instruments:
- 🔥 The compressor hums strongly, but does not start (you can hear a relay click).
- 🔥 The motor runs for a few seconds, then a click is heard and it stalls.
- 🔥 The compressor housing heats up to the point where it is impossible to touch it.
- 🔥 The smell of burnt insulation or burning near the refrigerator.
If you observe these signs, the probability that the continuity test will show a problem is close to 100%.
Frequent errors when diagnosing a compressor
Beginners often make mistakes that lead to false conclusions. The most common of them is measuring resistance without stripping the contacts. Oxide on studs can produce high resistance, which the technician mistakenly takes for a break. Always clean the contacts to a metallic shine before taking measurements.
The second mistake is ignoring the condition of the wires going to the relay. By ringing the motor, you can measure resistance through long wires, one of which is broken inside the insulation. As a result, you will get a break and decide that an expensive compressor has burned out, although the problem is in a cheap wire. Always check the circuit from probe to probe, eliminating unnecessary elements.
The third mistake is an attempt to start the engine without making sure that the starting device is working properly. If you have checked the windings and they are normal, but the refrigerator is not working, do not rush to change the compressor. Buy or build a test launch circuit. If the motor starts working on the table, then the problem is in the refrigerator electronics or thermostat.
⚠️ Attention: Technical characteristics and location of elements may vary depending on the refrigerator model. Before starting work, check the technical documentation or service manual for your specific device.
☑️ Checklist before replacing the motor
Replacement compressor: is it worth doing it yourself?
If the continuity test shows an open circuit, a short circuit or a breakdown in the housing, the compressor must be replaced. However, a nuance arises here: just screw on the new motor and plug it into the outlet it won't work. The refrigerator system is sealed and filled with freon. To replace you need:
- 🛠️ Cut off the old compressor (bleed off the gas).
- 🛠️ Solder a new motor (with an oxygen-propane torch).
- 🛠️ Vacuum the system (remove air and moisture).
- 🛠️ Fill the refrigerator with the exact amount of refrigerant.
These operations require special equipment and skills. Independent replacement without a vacuum sealer and a pressure gauge station will lead to rapid breakdown of the new unit.
Therefore, if an electrical check reveals a motor defect, it is better to entrust further work to professionals. You saved money on diagnostics, knowing exactly the cause of the breakdown, and now you can reasonably discuss repairs with the technician, knowing that they are not trying to sell you an “electronics test” when the “iron” motor burned out.
In conclusion, let us remind you: competent diagnostics with a multimeter allows you to weed out many false breakdowns. It often turns out that the motor is alive, but the problem is in the relay or wiring. But even if the motor is faulty, you will know this for sure and will be able to plan a budget for repairs or purchase of new equipment.
Is it possible to restore a burnt-out motor?
Theoretically, it is possible to rewind the windings, but in practice it is more expensive and more difficult than buying a new compressor. Factory sealing and balancing at home are irreversible.
Is it possible to check a compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without a device. You can only visually assess the integrity of the wires and the absence of burning. An attempt to turn it on “at random” can lead to a fire or electric shock if there is a breakdown in the case.
What resistance is considered normal for different brands?
For most household refrigerators (Indesit, Atlant, LG), the resistance of the working winding is 15-25 Ohms, the starting winding is 30-45 Ohms. For inverter compressors, the testing method is different, since the windings there have a different structure.
Why does it hum, but does not start?
This is a classic sign of a jammed piston group or a malfunction of the starting relay. If at the same time the current in the network increases sharply, and after a few seconds a click is heard, the thermal protection is triggered.
Is it dangerous to touch live pins?
Absolutely yes. 220V voltage is deadly. All connections and disconnections of wires should be made only with the refrigerator plug completely unplugged from the socket.