The situation when the refrigerator stops cooling or works intermittently always takes you by surprise, and the first suspicious unit is becomes the compressor, which is often mistakenly called simply an “engine”. It is this unit that is responsible for the circulation of the refrigerant, and if it fails, restoration repairs will require significant financial investments or a complete replacement of the equipment. Before calling a technician or scrapping the device, it is necessary to conduct a competent initial diagnosis to understand whether the problem really lies in the heart of the cooling system.
Checking the performance of the motor is a process that requires care, compliance with safety precautions and a basic understanding of electrical circuits. In this article, we will analyze in detail the algorithms for identifying malfunctions compressor, methods for checking windings and assessing the condition of the starting mechanism, which will allow you to save time and money on diagnostics.
Primary visual and acoustic diagnostics
Any repair work should begin with an external inspection, which often allows you to identify obvious defects without the use of complex instruments. Listen carefully to the sounds emanating from the unit: a working motor operates with a characteristic monotonous hum, while a faulty one may produce clicks, an intermittent hum, or complete silence when plugged in.
Inspect the back wall of the refrigerator in the area of the compressor for external damage, traces of oil or burning. The presence of oily stains may indicate depressurization of the system, which automatically makes further electrical checks pointless until the freon leak is eliminated. It is also worth checking the integrity of the wires going to the terminal box.
⚠️ Attention: If you notice traces of severe burning, melted insulation, or smell a strong smell of burnt plastic, it is dangerous to carry out further independent diagnostics. In this case, there is a high risk of a short circuit or fire, so it is better to limit yourself to a visual inspection and call a specialist.
An important step is checking the temperature conditions. If the engine hums, but there is no cold, or it turns on for a few seconds and immediately turns off with a click, this indicates specific problems. In the first case, there may be a freon leak or a clogged capillary tube, in the second - a malfunction of the start relay or a wedge of the piston group.
Preparation for testing and safety measures
Any manipulations with the electrical components of the refrigerator require strict adherence to electrical safety rules, since the voltage online poses a real threat to life. The first and mandatory step is to completely disconnect the device from the power supply by removing the plug from the socket. Do not rely only on switches or buttons on the case.
To carry out high-quality diagnostics, you will need a minimum set of tools that any home craftsman should have. The main device will be a multimeter (tester), which allows you to measure the resistance and integrity of circuits. You may also need screwdrivers to remove the protective casing and pliers.
- 🔌 Multimeter —the main device for measuring winding resistance.
- 🔧 Set of screwdrivers —for dismantling the protective box and removing the relay.
- 🧤 Dielectric gloves —additional protection when working with live parts.
- 📱 Smartphone with camera —to photograph the wiring diagram before disassembling.
Before starting work, it is recommended to let the refrigerator cool down if it has been running for a long time time, as the compressor can reach high temperatures. In addition, move the unit away from the wall, providing free access to the rear part where the motor-compressor is located.
Removing and checking the starting relay
Often the cause of engine failure is not the motor itself, but the starting relay, which provides an impulse to start. This compact unit attaches directly to the compressor housing and has electrical contacts. To check it, you need to remove the protective plastic or metal casing covering the back of the unit.
After removing the casing, carefully disconnect the wires going to the relay and remove the unit itself from the contact group of the compressor. Usually it is simply slipped over the terminals and secured with a bracket or latches. Visually inspect the relay: there should be no burning inside, and the contacts should be clean, without oxidation or carbon deposits.
⚠️ Attention: The starting relay has the correct installation orientation (usually marked with an UP or TOP arrow). If you install it back, the refrigerator will not start, and the relay may burn out. Remember or photograph its position before removing it.
The relay can be checked by shaking it near the ear: if a ringing is heard inside, it means the mechanism is damaged and requires replacement. More accurate diagnostics are carried out with a multimeter in dial mode, checking the integrity of the contacts depending on the position of the relay. If the relay is working properly, but the engine does not start, the problem most likely lies deeper.
Why does the relay click, but does not start the engine?
The click means that the electromagnetic coil of the relay is activated, trying to start the engine. If a second click (turning off) immediately follows, it means that the current in the winding circuit does not reach the required value to keep the relay in the on state. This may be due to an interturn short circuit, a wedge of the pistons, or low voltage in the network.
Testing the motor windings with a multimeter
The most reliable way to check the integrity of the electrical part of the motor is to measure the resistance of its windings. There are three terminals (contacts) located on the compressor housing, to which the starting relay is connected. They are usually marked, but if not, their arrangement is standard: two upper contacts and one lower (or they are arranged in a triangle).
Switch the multimeter to the resistance measurement mode (Ohm) to the 2 kOhm limit. Touch the probes to the pairs of contacts. With a good single-phase motor, you should get three resistance values between the three possible pairs of terminals. The sum of the two smaller resistances should be equal to the largest.
| Pair of contacts | Expected value (approximate) | Characteristics |
|---|---|---|
| Starting - Working | Maximum (sum) | Circuit impedance |
| Starting - General | Average | Starting winding resistance |
| Working - General | Lowest | Working winding resistance |
| Case - Any output | Infinity (1) | No breakdown to ground |
If the multimeter shows one (infinity) between any two terminals, this means winding breakand the engine cannot be repaired. If the device shows zero or a value close to zero where the resistance should be, then an interturn short circuit has occurred. It is also critically important to check that there is no breakdown on the case: the resistance between any terminal and the copper tube or case must be infinite.
☑️ Algorithm for checking the compressor
Diagnostics of mechanical faults and wedge
Electrical serviceability of the windings does not guarantee engine operation, since the problem may be mechanical in nature. If, when turned on, the refrigerator makes a dull humming sound, and then a shutdown click is heard, this often indicates a jammed piston group. The motor tries to start, but physically cannot turn the shaft.
There is a “wedging” method, which sometimes helps to revive the unit, although it is a temporary measure. The essence of the method is to apply voltage directly to the working winding (bypassing the starting relay) to create a powerful starting torque. However, this method is dangerous and requires the use of a special starting device or capacitor.
A safer, but more labor-intensive method is to try to develop the compressor mechanically, gently tapping the housing with a rubber mallet at different points, while simultaneously applying short-term current pulses. If the shaft is “stuck” due to frozen oil or microscopic chips, sometimes this helps to move it from a dead point.
⚠️ Attention: An attempt to start a “jammed” compressor directly from the network without a starting relay or capacitor can lead to instantaneous burnout of the windings or a fire. Do this only if you understand the risks and have the appropriate equipment.
If, after a successful start, the engine runs very loudly, with a metallic knock, this indicates serious wear and tear on the internal mechanisms. In this case, it is more economically feasible to replace the entire compressor, since the resource of such a unit has been exhausted.
Frequently asked questions and answers (FAQ)
Is it possible to check a compressor without a multimeter?
It is impossible to fully check the integrity of the windings without instruments. However, you can carry out an indirect check: connect a working start relay and apply power. If the engine hums and vibrates, but does not start, the problem is mechanical or in the relay. If there is silence and not even a buzz, a break is likely. But it is impossible to make an accurate diagnosis without a tester.
Why is the compressor hot, but the refrigerator does not freeze?
This is a classic sign of a refrigerant leak or a clogged system. The engine idles, trying to pump through the missing freon, which causes it to overheat. In this case, the electrical part of the motor is working, but the cooling system requires refueling and searching for the leak.
How much does it cost to replace the motor on a refrigerator?
The cost is the price of a new compressor (depending on the brand: cheaper for Atlant, more expensive for Liebherr or Bosch) and the cost of the work of a specialist. On average, replacement costs 40-60% of the cost of a new refrigerator, so repairs are often only advisable for premium appliances.
Can low voltage in the network kill a compressor?
Yes, prolonged operation at low voltage (less than 190V) leads to the fact that the starting relay cannot normally start the engine and windings overheat and insulation breakdown occurs. For protection, it is recommended to use a voltage stabilizer.
What to do if, after replacing the relay, the refrigerator started working, but after an hour it turned off?
Perhaps the new relay was selected incorrectly (they are available for different capacities and types of compressors) or the problem was not in the relay, but in the motor itself, which was heating up and the thermal protection was triggered. It is also worth checking the thermostat.