Sudden cessation of operation of the refrigerator or, conversely, its continuous hum without visible cooling are alarming signals indicating possible problems with the heart of the unit, that is compressor. It is this unit that is responsible for circulating the refrigerant through the system, creating the necessary pressure to remove heat from the chambers. When the equipment stops freezing, the first thing that comes to the owner’s mind is to call a technician, but the initial diagnosis can often be carried out independently, having a minimal set of tools and a basic understanding of the design of electrical appliances.
Before you begin disassembling and testing the contacts, it is necessary to exclude trivial causes of the malfunction, such as lack of voltage in the outlet or damage to the power cord. If everything is in order with the electricity in the house, and the refrigerator is silent or makes strange sounds, a visual inspection and checking the electrical parameters of the motor will be required. Diagnostics of the compressor allows you to understand whether the unit can be restored or requires an expensive motor replacement.
It is important to understand that working with electrical components and refrigerants requires compliance with safety precautions. Even if you do not plan to open the sealed circuit, access to the electrical part of the engine requires disconnecting the device from the network. In this article we will look in detail at how to identify a malfunction, what tools will be needed and what to look for when checking various types of motors.
Initial inspection and external signs of a malfunction
Diagnostics should always begin with an analysis of the external manifestations of the problem, as they often indicate the nature of the breakdown. If the refrigerator Indesit or Atlant hums, but does not start, or operates silently, but is warm inside, this may indicate various problems. In the first case, jamming of the piston group or a faulty start relay is often to blame; in the second, an open circuit or burnt out winding is to blame.
Pay attention to the temperature of the compressor housing during operation. If the motor is hot, but the refrigerator is not cooling, there may be a freon leak or a blockage in the capillary system. If the engine is cold and silent, the problem is most likely in the electrical part. Visual inspection also includes checking the integrity of the wires going to the terminal box and the absence of traces of burning or melted insulation.
⚠️ Attention: If you find traces of oil on the compressor housing or smell burning wiring, further use of the device should be stopped immediately. This may indicate depressurization of the system or critical overheating of the insulation.
Sometimes the malfunction does not appear immediately, but cyclically: the refrigerator turns on, runs for several minutes, then a click is heard and it turns off. This is a classic symptom of a thermal protection relay triggering, which turns off the power when the windings overheat or the rotor cannot start. In such a situation, it is important to determine why the motor cannot reach operating mode.
Necessary tools and preparation for diagnostics
To properly check the performance of the compressor, you will need a basic home repair kit. The main tool will be multimeter (tester), which allows you to measure the resistance of the windings and check the integrity of the circuit. Without this device, diagnostics will be only a superficial guess based on external signs.
In addition to the tester, prepare the following tools:
- 🔧 Screwdrivers (Phillips and flat) for removing the back cover and dismantling the compressor casing.
- 🔨 Pliers for carefully disconnecting terminals and wires.
- 💡 Test lamp (socket with a light bulb and two wires) to check the voltage supply.
- 🧤 Dielectric gloves to ensure safety when working with electricity.
Before starting work, be sure Unplug the refrigerator from the power supply. Access to the compressor is usually located at the lower rear of the unit. After removing the protective cover, you will see a black cylindrical or pear-shaped tank - this is the motor-compressor. Cooling system tubes and an electrical cable covered with a plastic casing are suitable for it.
Carefully remove the plastic casing from the start-up relay. Inside you will see contacts going to the compressor and the relay itself. This is where we will carry out the main measurements. It is critically important before any manipulations with the wires to make sure that the capacitors are discharged, although in modern household models the risk of getting an electric shock after disconnection is minimal, caution will not hurt.
☑️ Preparing to check the compressor
Checking the integrity of the motor windings multimeter
The most reliable way to determine the condition of the electrical part of the engine is to ring its windings. The compressor terminal block usually has three contacts: two for connecting the starting and operating windings and one common. To understand which one is which, you need to refer to the diagram on the relay body or use a multimeter in resistance measurement mode (Ohm).
The verification process is as follows: switch the multimeter to resistance measurement mode (200 Ohm or 2 kOhm limit). Touch the probes to the pairs of contacts. Between the common contact and the working terminal, the resistance should be the smallest (usually 10-20 Ohms), between the common and starting terminals - average (30-50 Ohms), and between the starting and working terminals - the sum of the two previous values. If the device shows one (infinity) or zero, this indicates an open or short circuit.
The table below will help you navigate the normal resistance readings for a working compressor:
| Pair of contacts | Normal resistance (Ohm) | Possible malfunction |
|---|---|---|
| Common - Working | 10 - 25 Ohm | Normal |
| Common - Starting | 30 - 60 Ohm | Normal |
| Starting - Working | The sum of the two is higher | Normal |
| Any pair - Housing | Infinity (∞) | Breakdown on the housing |
If, during the dialing, you find that the resistance between any of the contacts and the copper tube or compressor housing is not equal to infinity, then it has occurred insulation breakdown. It is strictly prohibited to operate such a refrigerator, as it is deadly. In this case, the engine is only subject to recycling or complex rewinding in the factory.
Diagnostics of the starting and thermal relay
Often the compressor itself is working, but cannot start due to a malfunction of the attached equipment. The starting relay is responsible for supplying an impulse to the starting winding at the moment of start, and the thermal relay protects the motor from overloads. In modern models, these devices are often combined into one unit, which is simply put on the compressor contacts.
To check the relay, it must be removed and the housing carefully opened (if the design allows this). Visually assess the condition of the contacts: there should be no soot, oxides or traces of melting on them. Inside the induction relay there is a coil and a movable core that must move freely. If the core is jammed or the coil is burned out, the relay will not work.
The integrity check can be carried out with a multimeter in continuity mode. The contacts must close in a certain position of the relay (usually in the operating position when the rod is facing up). If the circuit does not ring or, on the contrary, the contacts are constantly short-circuited, the part must be replaced. Cost of a new relay incommensurably lower than the cost of replacing the compressor, so it is often worth starting diagnostics with this unit.
Is it possible to start a compressor without a relay?
Theoretically, you can start the motor by applying voltage directly to the starting winding through a button, but doing this is extremely dangerous and is not recommended without experience. This can lead to instantaneous burnout of the winding or injury.
How to check a compressor for breakdown and jamming
One of the most unpleasant situations is mechanical jamming of the piston group. If the electrical part is intact, the windings ring, the relay is working properly, but the motor only hums and does not start, perhaps the rotor is jammed. In this case, the current in the circuit increases sharply, and thermal protection is triggered. Attempts to “pump up” such a compressor by applying increased voltage often lead to its final failure.
Checking for breakdown (short circuit to the housing) has already been mentioned when measuring resistance, but there is one more nuance. Sometimes breakdown occurs only under load or when heated. If, when you turn on the refrigerator, the circuit breaker in the panel immediately knocks out or the fuse blows, this is a sure sign of a short circuit inside the motor or in the wiring.
To check the mechanical part (without freon), technicians sometimes use the method of direct voltage supply, bypassing the relay, but only for a split second. If there is a powerful blow and hum, but there is no rotation, the compressor is jammed. If the shaft makes a revolution and the motor runs smoothly, the problem was in the relay. However, this method requires professional skills.
⚠️ Attention: Never leave the compressor running without the cooling system pipes connected (in the open air) for more than 30-40 seconds. The motors are cooled by circulating freon, and at “idle speed” without load they overheat and burn out in a matter of minutes.
Specifics of checking inverter compressors
Modern brand refrigerators LG, Samsung and Bosch often equipped with inverter compressors. Their diagnostics are fundamentally different from testing conventional linear motors. The inverter motor does not have a classic starting relay, and the rotation speed is controlled by an electronic unit (inverter).
You can ring the windings of the inverter compressor with a multimeter (they must have the same resistance to each other and not ring the housing), but you cannot start it directly. It requires a control signal of a certain frequency. If such a refrigerator does not start, first of all, check the voltage at the input to the inverter unit and the presence of errors on the control display.
Inverter systems more sensitive to power surges in the network. Often the cause of a breakdown is not the motor itself, but a burnt-out control module. At home, it is almost impossible to fully check the operation of an inverter compressor without a special test bench.
Frequent errors during self-diagnosis
Trying to save on calling a technician, refrigerator owners often make mistakes that turn simple repairs into a complex and expensive procedure. One of the most common is an attempt to replace the start relay “at random”, without checking the compressor itself. If the motor has an interturn short circuit, the new relay will burn out instantly.
Another mistake is ignoring the state of the capacitor (if it is in the circuit). A failed capacitor may not provide enough impulse to start, which is why the humming motor will go into protection. Also, do not forget about the integrity of the door seals: if they allow heat to pass through, the compressor will wear out, which will ultimately lead to overheating and failure.
Remember that replacing a compressor is not just unscrewing the bolts. This is a process that requires evacuating the system, charging it with freon, and using a torch to solder the copper tubing. If the diagnostics showed a malfunction of the motor itself, it is still better to contact licensed professionals to replace it.
Frequently asked questions (FAQ)
Can the compressor operate if there is no freon in the system?
Technically, the motor can start and operate without freon, but this will lead to its rapid overheating and jamming, since freon is involved in cooling the windings. In addition, working at “idle” without pressure will quickly damage the compressor.
Why does the compressor hum but does not start?
This can be caused by three main reasons: jamming of the piston group, a malfunction of the starting relay or an interturn short circuit in the windings, due to which there is not enough starting moment.
What resistance should a working compressor have?
The resistance of the working winding is usually 10-25 Ohms, the starting winding is 30-60 Ohms. The main rule: the resistance between the starting and operating contacts must be equal to the sum of the resistances of each winding relative to the common contact.
Is it dangerous to change the compressor yourself?
Yes, it is dangerous. The process involves working with high voltage, open flame (soldering) and gases under pressure. Improper soldering or filling can lead to an explosion or fire.