A sudden breakdown of a household refrigerator often causes panic, especially if there are large stocks of food inside. However, before calling a technician or looking for a replacement unit, it makes sense to conduct initial diagnostics, which in many cases allows you to identify the cause of the malfunction. One of the most important elements that ensure the circulation of refrigerant and maintain a low temperature is compressorwhich in everyday life is often called a motor or engine. It is its failure that most often leads to the fact that the refrigerator stops freezing, although the light inside is on.
Independent checking of this unit requires a minimum set of tools and compliance with safety precautions, but allows you to significantly save on diagnostics at the service center. In this article we will analyze in detail the algorithm of actions that will help determine whether your compressor is alive or the problem lies in the accompanying elements of the system. Correctly assessing the condition of the motor is the first step to a successful and budget-friendly repair.
It is worth noting right away that working with electrical components and refrigerants requires caution. If you are not confident in your abilities or see clear signs of serious damage to the wiring, it is better to stop at the visual inspection stage. However, for most equipment owners, checking the windings and starting relay is a completely feasible task that does not require deep knowledge in electrical engineering.
Primary diagnostics and visual inspection
Before taking up measuring instruments, it is necessary to conduct a thorough external inspection of the unit. Often the reason for failure lies not in the very heart of the refrigerator, but in a banal power failure or mechanical damage. Make sure the power cord is intact, the plug is not melted, and the outlet is working properly. Try plugging in another device, such as a hair dryer or lamp, into the same outlet to eliminate problems with the electrical network in the apartment.
Then inspect the back wall of the refrigerator where the compressor is located. Pay attention to the condition of the tubes: if you see oily stains or traces of leaks in the area of the fittings, this may indicate depressurization of the system. Start relay, put on the side of the compressor, should not have cracks, soot or traces of plastic melting. Any external damage to the wire insulation is also an alarming signal.
Plug in the refrigerator and listen. A working motor usually produces a smooth hum. If you hear a low hum that ends abruptly after a few seconds, or intermittent clicking sounds without the engine starting, this indicates a starting attempt that fails. This situation is often associated with jamming of the piston group or a malfunction of the starting device.
⚠️ Attention: If, when you try to start, you smell burning, see sparking or smoke, immediately disconnect the device from the network. Continued operation in this condition may result in a fire.
It is also important to check the temperature conditions. If the compressor runs continuously without turning off for hours, and the temperature in the chambers does not drop below +10 degrees, this may indicate a loss of motor performance or a freon leak. In this case, the engine itself may be electrically functional, but not be able to cope with the load.
Necessary tools and safety measures
To carry out high-quality diagnostics, you will need a basic DIY kit. The main tool will be multimeter (tester), which allows you to measure resistance and test circuits for open circuits. Without this device, the check will be only speculative. You may also need screwdrivers (Phillips and flathead), pliers and electrical tape.
Safety is the number one priority when working with household appliances. Before starting any manipulations, be sure to disconnect the refrigerator from the power supply. Even after unplugging, a residual charge may remain in the start relay capacitors, so do not touch the contacts with bare hands without first discharging them.
The refrigerator compressor is filled with oil, and the circulation system is under pressure. It is strictly forbidden to cut through or bend the copper tubes coming out of the motor housing. A leak will result in refrigerant leakage and require complex recharging by a specialist. Your task is to check the electrical part without interfering with the hydraulic system.
If you plan to remove the starting relay, prepare a container to drain possible condensate or oil that could leak inside the casing. Work in a well-lit place and use tools with insulated handles.
Checking the starting and protective relays
Often the culprit for starting problems is not the engine itself, but the attachments. The starting relay is responsible for supplying a pulse to the starting winding, and the thermal relay protects the motor from current overloads. These elements are located in a black plastic or metal housing on the side of the compressor. Remove the protective casing and carefully dismantle the relay by pulling it down and to the side.
Visually inspect the insides of the relay. If soot, soot, or melted plastic is visible inside, the part requires replacement. Mechanical relays (with a posistor) can be checked by shaking them near the ear: if you hear the sound of broken insides, the relay is faulty. For more accurate diagnostics, use a multimeter in resistance measurement mode.
Ring the relay contacts. The resistance between certain contacts must be close to zero (short) or match the value indicated on the diagram. If the meter shows infinity where there should be a connection, the circuit is broken. The thermal relay is also checked for current flow: in a cold state it should ring.
- 🔌 Contact group: check whether the terminals suitable for the relay are oxidized and whether they are seated tightly.
- 🌡️ Temperature coefficient: posistor relays change resistance when heated, check their operation without applying voltage difficult, so it is often easier to replace with a new one.
- 🛡️ Case integrity: cracks in the plastic of the relay can allow moisture to pass through, which leads to a short circuit.
If the relay is working properly or the situation has not improved after replacing it, it is necessary proceed to checking the compressor itself. Often replacing a cheap relay brings the refrigerator back to life, so do not ignore this stage.
Diagnostics of the motor windings with a multimeter
This is the most important test step, allowing you to determine the condition of the electrical part of the motor. There are usually three contacts on the compressor housing, covered with a cover. By removing the cover and disconnecting the wires (after photographing the connection diagram), you will gain access to the winding terminals. They may be marked with letters or arranged in a triangle.
Switch the multimeter to resistance (Ohms) measurement mode. You need to find the common point and measure the resistance between it and the other two contacts. Typically, one winding has a lower resistance (working), and the other has a higher resistance (starting). The sum of the resistances of the two windings should be approximately equal to the resistance between the two extreme contacts.
It is critically important to check that there is no breakdown on the housing. Press one multimeter probe to the cleaned area on the compressor body (where there is no paint), and with the other touch all three contacts one by one. The device should show infinity. If you see any resistance values, it means that the insulation is broken and the motor is “breaking through” to ground. It is dangerous to use such a unit.
| Measurement type | Normal reading | Failure sign |
|---|---|---|
| Working winding | 10–30 Ohm | Infinity (break) or 0 (short circuit) |
| Start winding | 30–90 Ohm | Infinity (break) or 0 (short circuit) |
| Breakdown on body | Infinity (∞) | Any resistance values |
| Interturn short circuit | Stable values | Values are much lower than normal |
If the resistance of the windings corresponds to the norm and there is no breakdown to the housing, the electrical part of the engine is most likely in good condition. However, this does not guarantee the mechanical serviceability of the piston group.
☑️ Checking the windings
Analysis of current consumption and mechanical jamming
There are situations when the windings are intact, the relay is working properly, but the compressor hums and does not start, or the circuit breaker immediately knocks out. This may indicate a mechanical wedge of the piston group or an interturn short circuit, which only appears under load. For accurate diagnostics in this case, an ammeter (clamps) is required.
Connect the ammeter to the open circuit of the compressor power supply (usually to the operating winding circuit). When starting a working engine, the current briefly jumps and then drops to the rated value (usually 0.5–1.5 A depending on the power). If the current immediately increases to 3–5 A or more, the thermal relay is activated, turning off the motor. This is a sure sign of a short turn or wedge.
⚠️ Attention: Current measurements are carried out at a voltage of 220V. Be extremely careful not to touch live parts with your hands while the device is operating.
There is a “wedging” method, when increased voltage or impulse is applied to the motor in order to break the jammed piston. However, this method is dangerous and can completely kill the compressor. At home, it is safer to try to gently tap the motor housing with a rubber mallet in the mounting area while it tries to start. Sometimes this helps to move the piston.
Is it possible to start a compressor without a relay?
Theoretically, you can apply voltage directly to the working and starting windings, but this must be done very briefly (no more than 1-2 seconds), otherwise the starting winding will burn out. This method is suitable for diagnostics, but not for continuous operation.
If the engine starts, but runs very loudly, with a metallic knock, this indicates destruction of the internal suspension or valve group. Such a unit must be replaced, since repairs are not economically feasible.
Interpretation of results and final conclusions
Summarizing the diagnostic results, the condition of the engine can be classified. If the multimeter shows a break in the winding or a breakdown in the housing, the compressor is considered faulty and requires replacement. It is impossible to restore a burnt winding at home. In this case replacing the compressor is the only solution, which also requires replacing the filter-drier and refilling the system with freon.
If the electrical parameters are normal, but the motor does not start or consumes a huge current, a mechanical wedge is likely. Attempts to revive such a unit rarely produce long-term results. It is much safer to install a new or reconditioned compressor so as not to risk products and wiring.
If all checks are successful, but the refrigerator does not freeze, the problem may not lie in the engine, but in a refrigerant leak or a clogged capillary tube. Then the compressor may be in good working order, but run idle or constantly, without creating cold.
Competent diagnostics allows you to avoid purchasing unnecessary spare parts and accurately formulate the problem when contacting service. Remember that even with a successful electrical check, tampering with the refrigerant circulation system requires a license and special equipment.
Frequently asked questions (FAQ)
Is it possible to check a compressor without a multimeter?
It is impossible to accurately determine the health of the windings without instruments. However, you can carry out an indirect check: connect the motor directly to the network through a working relay (following the diagram). If it starts and runs smoothly, the electrical system is most likely ok. But this method is risky and does not guarantee the absence of breakdown on the housing.
Why is the compressor hot to the touch?
In operating condition, the compressor heats up to 60–90 degrees Celsius, which is the norm for sealed units. However, if it is red-hot or has a burning smell, this is a sign of overload, a wedge, or a problem with the cooling system of the engine itself.
How much does it cost to replace a compressor?
The cost consists of the price of a new unit, the work of a technician, refilling with freon and replacing the filter. On average, this represents a significant portion of the cost of a new refrigerator. If the equipment is more than 10 years old, it is often more profitable to buy a new device.
Can a faulty thermostat simulate a motor breakdown?
Yes, if the thermostat does not close the contacts, the signal to turn on will not go out, and the motor will not start, although it itself is working. Therefore, before checking the engine, always make sure that 220V voltage is supplied to the compressor terminals when the thermostat is turned on.