Has the refrigerator stopped cooling, and the motor is humming or, conversely, silent? In most cases, the problem lies precisely in compressor or in its launch system. Before calling a technician or buying new equipment, it is worth conducting basic diagnostics. The key tool here is the usual multimeter, which allows you to determine the state of electrical circuits in a matter of minutes.
The verification process requires compliance with safety precautions and an understanding of the principle of operation of the electric motor. The voltage of 220 Volts is deadly, so all manipulations are carried out only with the device completely disconnected from the network. In this In this article we will analyze an algorithm of actions that will help you understand whether the motor is alive or it’s time to change it. The video instructions built into the material will clearly demonstrate each stage.
The operating principle and design of the electric motor
To effectively troubleshoot the problem, you need to understand what exactly you are check. Asynchronous motor the refrigeration compressor has two main windings: working and starting. They are wound with copper wire and have different resistances. The working winding is made of a thicker wire and has less resistance, and the starting winding is thin, so its resistance is higher.
These windings are connected through a special device - a starting relay. It is this that switches phases and starts the motor. If the relay is working properly, but the refrigerator does not turn on, the problem may be a broken wire inside the motor or, worse, an interturn short circuit. In the latter case, the engine may hum, but not start, or the machine in the panel may be knocked out.
The compressor housing is sealed, and the windings can only be reached through the contact group brought out. Typically these are three contacts arranged in a triangle. It is important not to confuse their purpose, although this is not critical for the initial connection to a break. Knowledge of the device helps to avoid fatal errors during diagnosis.
Types of compressors
Modern refrigerators use inverter and linear compressors. Inverter models are more difficult to diagnose, since they are controlled by an electronic unit, and a simple test with a multimeter may not give a complete picture of the state of the system.
Necessary tools and preparation for work
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be multimeter (tester). He must be able to measure resistance (Ohm) and check the continuity of the circuit (continuity mode with a sound signal). Without this device, checking will be impossible or extremely unreliable.
You will also need screwdrivers to remove the rear protective panel of the refrigerator and the casing from the compressor itself. In some models Atlgant, Indesit or Bosch access to the motor may be limited, and additional elements will need to be removed. Do not forget to prepare insulating tape and, possibly, a new starting capacitor for testing if the old one is in doubt.
Before starting work, be sure to disconnect the refrigerator from the power supply. Unplug the plug from the socket. This is the golden rule of safety. Even if you plan to simply remove the cover, the risk of electrocution from faulty wiring remains high. Let the unit stand for 10-15 minutes for the capacitors to discharge.
☑️ Preparation for diagnostics
Dismantling and access to the contact group
After the refrigerator is turned off, you need to gain access to the “heart” of the unit. Remove the rear metal grille or panel that covers the bottom of the chassis. It is usually secured with several screws or latches. Be careful not to damage the condenser tubes located nearby.
On the compressor you will see a black casing (cap) covering the electrical part. It can be plastic or metal. Remove it by unscrewing the mounting screw or snapping the latches. Under the casing you will see a start relay and a thermal relay mounted on three pins of the compressor contact group.
Carefully remove the start relay. It is usually simply held together with a metal bracket or held on with latches. Do not pull sharply to avoid damaging the wires. After removing the relay, you will see three contacts protruding from the motor housing. These are the ones we will call.
⚠️ Attention: A residual electrical charge may remain on the relay contacts and capacitors. Before touching the multimeter with your hands or probes, it is recommended to briefly close the contacts with a screwdriver with an insulated handle to avoid sparks and unpleasant sensations.
Algorithm for testing the windings with a multimeter
Now we move on to the most important part is the measurements. Switch the multimeter to resistance measurement mode (limit 2 kOhm or 20 kOhm). If there is a dialing mode (beeper), you can use that, but the numbers on the screen will give more accurate information. The probes must be in good working order: when they are connected to each other, the device should show zero or a value close to it.
The compressor contact group usually has three terminals, forming a triangle. You need to ring them in pairs with each other. That is, measure the resistance between the first and second, first and third, second and third contacts. Record the resulting values. In a working motor, you should see three different resistance values.
The sum of the two smaller resistances should approximately equal the largest resistance. For example, if between contacts A-B there are 20 Ohms, A-B 50 Ohms, then between B-C there should be about 70 Ohms (20+50). This corresponds to the sum of the resistances of the starting and operating windings. If the device shows infinity (1 or OL on the screen), it means there is an open circuit.
Here are approximate values for different types of motors:
| Winding type | Resistance range (Ohm) | Characteristics |
|---|---|---|
| Starting | 30 - 60 Ohm | Thin wire, high resistance |
| Working | 10 - 25 Ohm | Thick wire, low resistance |
| Common circuit | 40 - 80 Ohm | Sum of starting and working |
| Case (breakdown) | Infinity | There should be no contact with the housing |
Checking for breakdown of the housing and interturn short circuit
One of the most dangerous malfunctions is breakdown of the winding insulation on the compressor housing. In this case, voltage may appear on the metal casing of the motor, which is fatal to humans. This is easy to check: press one probe of the multimeter to any of the three contacts, and the second to a cleaned place on the metal body of the compressor (where there is no paint or rust).
The device should show infinity (one in the most significant digit). If you see any resistance values or hear a squeaking sound, the insulation is broken. Operate such a refrigerator strictly prohibited. Even if it somehow starts, the risk of electric shock when touching the case or even being close (if the floor is wet) is too great.
An interturn short circuit is more difficult to detect. It manifests itself when the turns of the winding close together, reducing the total resistance. In this case, the motor can hum, get very hot and quickly fail. An accurate diagnosis often requires measuring the current consumption with special clamps, but this is indirectly indicated by a discrepancy between the winding resistances and the tabular data or a burning smell.
⚠️ Attention: Do not try to “revive” a compressor with a breakdown on the housing by grounding it. This is a temporary and dangerous measure. The only solution is to replace the unit.
Diagnostics of the starting relay and capacitor
Often the compressor itself is working, but the problem lies in the starting relay. This device is responsible for supplying an impulse to the starting winding. Inside the relay there is a coil and contacts that can burn or stick. Visually inspect the relay: if you can see carbon deposits, black spots inside, or smell burnt plastic, it needs to be replaced.
You can check the relay by shaking it near your ear. If a ringing sound is heard (as if from a broken part), it means that the mechanism is destroyed. You can also ring the relay contacts in different positions, but the easiest way is to replace it with a known good one of the same marking. The cost of the relay is low, and it is often the reason that the engine does not start.
If your model uses a starting capacitor, check it for swelling or electrolyte leakage. You can ring the capacitor with a multimeter in resistance measurement mode: when connecting the probes, the resistance should increase smoothly and then go to infinity. If the device immediately shows zero or infinity, the capacitor is faulty.
Relay marking
Relays are selected not only by the brand of the refrigerator, but also by the model of the compressor. Pay attention to the numbers and letters on the case (for example, RTK, R-3, PTC).
Interpretation of results and common errors
After all the measurements, you need to draw conclusions. If the windings ring, the resistances correspond to the norm, and there is no breakdown to the housing, it means that the electrical part of the motor is working. In this case, the reason for the refrigerator not working may be in the thermostat, control unit or freon leak.
However, if you find a break (infinity between the contacts), this indicates a burnt out winding. It is impossible to restore it at home; the compressor needs to be replaced. A common mistake made by beginners is poor contact of the multimeter probes with the leads. Clean the contacts with fine sandpaper before measuring to eliminate oxides.
Also remember that some modern inverter compressors (for example, in refrigerators Lg or Samsung) have three windings and are controlled by complex electronics. Their continuity is different: the resistance between all three terminals must be the same. If the values differ greatly, the motor is faulty.
⚠️ Attention: Technical characteristics and connection diagrams may vary depending on the specific refrigerator model and year of manufacture. Always check the manufacturer's technical documentation to obtain accurate data on winding resistance.
Frequently asked questions (FAQ)
Is it possible to check a compressor without a multimeter?
It is impossible to qualitatively check the windings without a device. You can only indirectly judge the condition: if, when plugged into the network (for a short time!), the motor hums and knocks out the machine, there is probably a short circuit. But this method is dangerous and does not provide accurate information about the integrity of the windings.
What resistance is considered normal for a working compressor?
The norm depends on the power of the motor. Typically, the resistance of the working winding is 10-25 Ohms, the starting winding is 30-60 Ohms. The main rule: the sum of the resistances of the two smaller circuits must equal the largest value. What is more important is not the absolute numbers, but their ratio and the absence of breakdown on the case.
What to do if the multimeter shows one?
A unit in the most significant digit of the multimeter screen means infinite resistance, that is, an open circuit. If such a picture is observed between any two contacts of the compressor (with the relay disconnected), it means that one of the windings has burned out and the motor must be replaced.
Can a compressor be electrically operational, but not work?
Yes, this is possible. This is called a mechanical wedge. The pistons are stuck inside the cylinders due to exhaustion or lack of oil. Electrically, the windings are intact, but the motor cannot turn the shaft. Sometimes the “pinging” method (applying increased voltage) helps, but this is a temporary solution.