A sudden increase in temperature in the refrigerator compartment often becomes an unpleasant surprise, forcing the owner to guess about the causes of the breakdown. In most cases, the culprit is compressor, which has stopped starting or works intermittently. Before calling a technician or buying new equipment, it makes sense to carry out initial diagnostics yourself in order to understand the scale of the problem and the cost of possible repairs.
Checking the motor requires care and compliance with basic electrical safety rules, since you will be working with live devices. Do not rush to disassemble the unit completely - sometimes the reason lies in banal oxidation of contacts or failure of a cheap starting relay. Understanding the principles of operation of an electrical circuit will help you save time and money, as well as make an informed decision about the advisability of restoring old equipment.
In this article we will analyze in detail the algorithm of actions that will allow us to identify a malfunction electric motor or related elements of the system. You will learn how to use a multimeter to test the windings, learn how to assess the condition of the start-up relay, and understand in which cases independent repair is no longer possible. Competent diagnostics is the first and most important step to returning cold to your home.
External signs of a compressor malfunction
The first stage of diagnosis is always a visual inspection and analysis of the sound of the unit. If the refrigerator hums, but does not generate cold, or there is complete silence, this already gives the first clue. Pay attention to the nature of the sounds: a steady hum followed by clicks may indicate startup attempts that are blocked by protection.
Inspect the back wall of the refrigerator, where compressoris located. In operating condition, the metal body of the motor should be warm, but not red-hot to the point where it is impossible to touch it. Excessive heating often indicates an interturn short circuit or jamming of the piston group, which requires immediate disconnection of the device from the network.
⚠️ Attention: If you smell burnt wiring or see sparking in the motor area, immediately unplug the cord from the outlet. Further operation of such a device may lead to a fire.
It is also worth checking the integrity of the tubes and the absence of oily leaks around the compressor housing. Oil can leak through the seals due to severe overheating or mechanical damage, which often leads to loss of refrigerant and final failure of the system.
Diagnostics of the starting relay
Often the motor itself is working, but cannot start due to a malfunction of the starting relay. This small element is responsible for supplying an impulse to the starting winding and protecting the motor from overloads. To check it, you need to remove the plastic casing from the compressor and carefully remove the relay, which is usually attached to three contacts.
Visually inspect the relay body for cracks, signs of burning or melted plastic. If you hear the sound of an object rolling inside (in a relay with a posistor or induction type), this may be normal, but the presence of carbon deposits on the contacts is a bad sign. Stripping the contacts sometimes helps to revive the device, but it is safer to replace it with a new one.
For an accurate check, you can use a multimeter in dial mode. The contacts must "ring" in a certain position, corresponding to a normally closed or open state, depending on the design. If the circuit does not ring or, on the contrary, rings constantly without opening, the relay must be replaced.
Is it possible to start a refrigerator without a relay?
Theoretically, you can start the motor by applying voltage directly to the windings, but doing this is strictly not recommended without special skills. This can lead to burnout of the windings or electric shock, since overheating protection will not work in this case.
Checking the motor windings with a multimeter
The most reliable way to understand the condition of the “heart” of the refrigerator is to check the resistance of the windings using multimeter. To do this, you need to remove the terminal block from the three pins coming out of the compressor and switch the device to resistance measurement mode (Ohms). There is often a diagram on the case indicating which pin is responsible for what, but this can also be determined experimentally.
Find a pair of contacts with the highest resistance - these will be the ends of the starting and operating windings. The third contact, which remains free, is common. By measuring the resistance between the common contact and the other two, you will get the values for the operating and starting windings, respectively. The resistance of the working winding is usually less than the starting winding.
☑️ The order of testing the windings
If the device shows infinity (open circuit) or zero (short circuit) on any of the windings, the motor is faulty. Also a critical parameter is the resistance between the compressor housing and any of the contacts - here the multimeter should show infinity. The presence of conductivity on the case indicates an insulation breakdown, which makes operation dangerous.
Table of normal resistance values
For correct interpretation of the data obtained, it is useful to check with typical values typical for most household refrigerators. However, remember that specific numbers may differ depending on the power and model compressor.
| Winding type | Resistance range (Ohm) | Nature of malfunction |
|---|---|---|
| Operating winding | 10 – 35 Ohm | Open or short circuit during deviation |
| Starting winding | 20 - 60 Ohm | Open or short circuit during deviation |
| Winding to the body | Infinity (∞) | Insulation breakdown (any value) |
| Thermal relay (thermal) | 0 Ohm (closed) | Open circuit during heating |
If your measurements differ radically from the tabulated data, the probability of failure of the electrical part of the engine is extremely high. In such a situation, further operation is impossible without replacing the unit.
Analysis of the operation of the thermostat and power circuit
Before sinning on the motor, make sure that the voltage reaches it at all. A common cause of a “silent” refrigerator is a faulty thermostat or defrost sensor in No Frost systems. If the circuit is broken at the thermostat level, the compressor simply will not receive a command to start.
You can check the thermostat by closing its contacts directly (temporarily!). If after this manipulation the refrigerator hums and begins to freeze, then the problem lies in the temperature sensor, and not in the motor. This is true for models with mechanical control, where the thermostat is a separate unit with a capillary tube.
In modern models with electronic control, the situation is more complicated: control moduleis responsible for turning on the compressor. If the board does not send a signal, the motor will not stop. Checking the module requires special knowledge, so in such cases it is better to limit yourself to a visual inspection of the board for swollen capacitors or burnt tracks.
⚠️ Attention: Closing the thermostat contacts is only permissible for a short time for diagnostics. Leaving the refrigerator in this mode without control, you risk bringing the food to complete freezing or overloading the system.
Mechanical problems: wedge and pressure
There are situations when the electrical part is completely intact: the windings are intact, the relay is working, there is voltage, but the motor does not start or hums, jerks and turns off. This is a sure sign of mechanical jamming of the piston group or high pressure compressor.
Attempts to “unwedge” the motor by applying increased voltage or striking the body often give only a temporary effect. Internal wear of rubbing parts, metal shavings getting into the oil or jamming of valves are irreversible processes. An attempt to forcefully start a jammed compressor is almost guaranteed to lead to final combustion of the windings.
Sometimes the cause of high pressure is a blockage in the capillary tube or filter-drier. In this case, the motor tries to push the freon, but cannot, which is perceived as a wedge. Diagnosis of a blockage requires connecting a pressure gauge manifold and checking the pressure in the system.
Frequently asked questions about diagnosing refrigerators
Is it possible to replace the compressor yourself?
Theoretically, it is possible if you have the skills to work with copper tubes, a blowtorch and a vacuum pump. However, the process requires refrigerant charging, which cannot be done efficiently without special equipment and a license. In addition, improper soldering will lead to freon leakage.
Why does the new compressor hum loudly?
Modern models can be noisier than their old Soviet counterparts due to changes in the design of the valves and the absence of a massive external casing. If the hum is not accompanied by vibration of the cabinet, this may be normal for a particular model motor.
How long should the motor run after turning on?
The operating time depends on the load of products and the temperature in the chamber. Typically the cycle lasts from 15 to 40 minutes, followed by a pause. If the refrigerator runs non-stop for days, this indicates a freon leak, compressor wear, or a violation of the thermal insulation.
Is it dangerous to check energized windings?
It is strictly forbidden to measure the resistance of the windings when the device is connected to the network. All measurements with a multimeter in Ohmmeter mode are carried out only on equipment that is completely de-energized and disconnected from the socket.