Sudden silence in the kitchen, where the refrigerator usually hums, or, conversely, a continuous hum without cooling - these are the first alarm signals for any owner of household appliances. Most often, the cause of failure is compressor, which is the heart of the entire cooling system. If the engine stops starting or works intermittently, food begins to deteriorate, and the ice melts in the freezer.
Before calling a technician or buying a new unit, it is worth conducting initial diagnostics yourself. In many cases, the problem lies not in the burnt out winding, but in the starting relay or thermostat, the replacement of which is much cheaper. In this article we will look at how to check the refrigerator compressor, what tools you will need and what to pay attention to during a visual inspection.
It is important to understand that electrical safety when working with household appliances comes first. Any manipulations inside the housing should be carried out only after the device has been completely disconnected from the power supply. Even if it seems to you that the device is completely de-energized, the residual voltage in the capacitors can be dangerous.
Initial visual inspection and analysis of symptoms
Diagnostics always begins with an external examination and analysis of the behavior of the refrigerator. If the unit hums but does not cool, or starts for a few seconds and immediately turns off, this indicates a specific range of problems. Pay attention to the casing temperature compressor: if it is excessively hot to the touch (burns your hand), the thermal protection may have tripped or the piston has jammed.
Sometimes the reason for the lack of cold is not the motor itself, but a freon leak. In such cases, the engine may run continuously, trying to gain temperature, but there will be no effect. Check the integrity of the tubes and the absence of oily stains in the lower part of the unit, since oil often escapes along with the refrigerant through the depressurization point.
⚠️ Attention: If you find black carbon deposits or melted plastic in the area of the motor connection contacts, under no circumstances try to turn on the device immediately. This is a sign of a short circuit that could damage the wiring inside the wall or the socket.
It is also worth listening to the sounds that the equipment makes. A healthy unit operates with a uniform, low hum. A knock, clanging or sharp metallic grinding sound indicates mechanical destruction of internal components. The table below shows the main symptoms and their probable causes:
| Symptom | Probable cause | Difficulty of repair |
|---|---|---|
| Buzzes, but does not start | Faulty starting relay or the piston is jammed | Medium |
| Clicks and turns off | Thermal relay or interturn short circuit has tripped | High |
| Works constantly without stopping | Freon leakage or compression wear | High |
| Strong vibration and noise | Destruction of the motor suspension or shock absorbers | Low |
Check serviceability of the starting relay
Before “climbing” into the motor itself, it is necessary to rule out a malfunction of the starting relay. This small element is responsible for supplying a starting pulse to the motor winding. If the relay is “stuck” or burned out, the compressor simply will not receive a signal to start, although electricity will flow to it.
To check, remove the relay from the compressor fitting (usually it is fixed with a bracket or latches). Shake the device next to your ear: if you hear a clear knocking or ringing sound inside, the core is broken and needs to be replaced. Visually inspect the contacts for carbon deposits - black color indicates poor contact and overheating.
There is a simple way to check the functionality of the relay without complex instruments, but it requires caution. It is possible to apply voltage directly to the windings, bypassing the relay, but this should only be done if you are confident in your electrician skills. A safer method is to test the tester in resistance measurement mode.
If the relay is working properly, but the motor is still silent, the problem lies deeper. Often, owners change a relay without checking the windings, and wonder why the new element immediately burns out. Therefore, the next stage is checking the electrical circuit of the motor itself.
Diagnostics of the windings with a multimeter
The most accurate way to determine the condition of the electric motor is to measure the resistance of the windings using a multimeter. To do this, you need to remove the back cover of the refrigerator, gain access to the contact group of the compressor and disconnect the wires. Before starting work, make sure that the device is switched to resistance measurement mode (Ohm) to a limit of 2 kOhm.
A standard single-phase compressor has three terminals: common, starting and working. You need to “ring” them in pairs with the multimeter probes. Normal resistance readings vary depending on the power of the motor, but are usually:
- 🔌 Between the working and common terminals: from 15 to 35 Ohms.
- 🔌 Between the starting and common terminals: from 30 to 50 Ohms.
- 🔌 Between the starting and working terminals output: the sum of the two previous values.
If the device shows one (infinity) in any of the sections, this means winding break. In this case, the current simply does not flow through the coil, and the motor cannot create a magnetic field to rotate the rotor. Repair at home is impossible; rewinding or replacement of the unit is required.
It is worse if the multimeter shows zero or a value close to zero. This indicates turn-to-turn short circuit. The insulation between the turns of the wire is broken, the current flows along the shortest path, causing overheating and knocking out the plugs. Such a compressor often hums, but does not start, and when trying to start it can spark.
☑️ Check with a multimeter
Checking for breakdown on the body
Particular attention should be paid to checking for “breakdown”. This is a situation where voltage comes into contact with the metal housing of the compressor or refrigerator. This not only disables the equipment, but also creates a direct threat to human life when touching the case.
To check, switch the multimeter to the resistance measurement mode at the maximum limit (usually 2 MOhm or 20 MOhm). Press one probe to the cleaned area on the compressor body (where there is no paint or rust), and with the second touch any of the three contacts on the terminal block.
The device should show infinity (one in the most significant digit). If you see any resistance values, even very large ones, or the device makes a squeaking sound, then the insulation is broken. It is strictly prohibited to operate such a refrigerator ⚠️ Attention: In older models of refrigerators without grounding, a breakdown on the body may not be felt immediately. Modern mandatory presence of a grounding circuit in the socket. If you do not have grounding, use a differential circuit breaker (RCD) for protection. until the fault is eliminated.
⚠️ Attention: In older models of refrigerators without grounding, a breakdown on the body may not be immediately felt. Modern mandatory presence of a grounding circuit in the socket. If you do not have a ground, use a residual current circuit breaker (RCD) for protection.
Mechanical check: test with a pressure gauge
If the electrical part is in perfect order (no breaks or short circuits), but the refrigerator does not cool, the mechanical part - the piston group - may have worn out. The compressor may hum, creating the appearance of operation, but not pumping pressure into the system. For accurate diagnostics, you need a pressure gauge manifold.
The checking process is as follows: a pressure gauge hose is connected to the service fitting (usually on the back side of the compressor). When you turn on the engine, the gauge needle should go up sharply, indicating an increase in pressure. For household refrigerators, a discharge pressure of around 15-20 atmospheres is considered normal (depending on the type of freon).
If, when the engine is turned on, the pressure does not increase or increases very slowly, there is a loss of compression. The reasons may be different:
- 💨 Wear of piston rings or valves.
- 💨 Scuffing on the cylinder or piston.
- 💨 Broken valve plate.
Is it possible to restore compression?
There are traditional methods of adding special additives to the oil or vacuuming the system, but in 95% of cases this is a temporary measure. Mechanical wear of the metal cannot be cured with chemistry; the unit must be replaced.
Also, with a mechanical malfunction, it is often observed when the compressor starts, runs for 10-20 seconds, then a click is heard (the thermal relay is activated) and it goes silent. After cooling, the cycle repeats. This is a sure sign that it is too difficult for the motor to turn the shaft or pump freon.
Causes of frequent breakdowns and prevention
Understanding the causes of failure helps extend the life of a new compressor. The most common reason is overheating. It occurs when the refrigerator is located close to the wall, in a niche without ventilation, or next to heating appliances. Heat is not removed from the capacitor, the load on the motor increases, and it burns out.
The second common reason is power surges in the network. The electronics of modern refrigerators are sensitive, but older models also suffer from unstable power supply. Using a voltage stabilizer or at least a voltage control relay (VCR) can save an expensive unit.
The third reason is violation of defrosting rules. Many users, wanting to speed up the process, chop the ice with a knife or pour hot water. This leads to deformation of the evaporator tubes and moisture entering the system, which causes corrosion and acidification of the oil in the compressor.
Regular cleaning of the condenser (grid at the back of the refrigerator) from dust and animal hair is also critically important. A heat exchanger clogged with dust cannot effectively transfer heat, which causes the compressor to wear out.
FAQ: Frequently asked questions
Is it possible to repair a burnt-out compressor yourself?
Theoretically, it is possible to rewind the windings or replace the valves, but this requires special equipment, vacuum pump and skills. The cost of spare parts and labor often exceeds the price of a new compressor, so in 90% of cases a complete replacement of the unit is recommended.
Why does a new compressor hum louder than the old one?
Modern models may have a different sound insulation design or simply be more powerful. However, strong knocking or vibration is not acceptable. Check whether the tubes are touching the refrigerator body and make sure that the shock absorbers are installed correctly.
How long can you store a refrigerator with a faulty compressor?
You can store it indefinitely if freon and oil have not left the system. However, if depressurization occurs, moisture may get inside the system, which will require expensive nitrogen purging before installing a new motor.
Will an inverter compressor replace a conventional one?
Yes, but this requires replacing not only the motor, but also the control board, since their operating principles are different. A conventional compressor operates in cycles (on/off), and an inverter compressor regulates power smoothly.
Is it dangerous to breathe freon vapors when checking?
Freon is odorless and non-toxic in small quantities, but it displaces oxygen. In a confined space, a large leak may cause suffocation. In addition, upon contact with an open fire, freon decomposes to form phosgene, a chemical warfare agent.