A sudden stop in the refrigerator is always stressful, because food supplies and the family budget are at risk. The first thing owners of units often do is blame the electrical network or thermostat, forgetting that the heart of the cooling system is compressor. It is this unit that creates the pressure necessary for the circulation of the refrigerant, and if it fails, the cold ceases to be produced completely.
Before calling a technician or looking for a new unit, it makes sense to carry out initial diagnostics yourself. Many faults, such as a stuck start relay or a broken winding, can be identified visually or using a simple multimeter. A correct assessment of the condition of the motor will help you understand whether it is worth repairing the equipment or whether it is easier to purchase a new one.
In this article we will analyze in detail the algorithm for checking the compressor, consider the typical symptoms of its breakdown and explain how to safely measure electrical parameters. You will learn what sounds you should pay attention to and why overheating of the case can be a critical signal.
Primary diagnostics: sounds, temperature and visual inspection
You should start checking long before you pick up the tools. Careful observation of the behavior of the refrigerator can provide up to 50% of information about the condition motor-compressor. Come close to the unit and listen. A working refrigerator operates cyclically: after a period of silence, a quiet hum is heard, turning into a steady hum, then the cycle repeats.
If you hear a click, followed by a hum lasting 2-3 seconds, and then another click and silence, this is a bad sign. This picture often indicates that starting relay tries to start the engine, but the compressor is jammed or the winding is burned out. It is also worth paying attention to the temperature of the rear wall or grill of the condenser: if the motor hums constantly, but there is no cold, and the grill is barely warm, there may be a freon leak or a leak in the system.
⚠️ Attention: If you feel a strong tingling current when you touch the compressor housing, immediately unplug the refrigerator. Operation of such a device is deadly, since the insulation of the windings or grounding is broken.
Visual inspection is also important. Remove the back panel (if equipped) and inspect the compressor. There should be no traces of oil, deep rust or melted wire insulation. The presence of oily spots around the stem or tubes may indicate depressurization of the seals, which requires replacing the unit.
Checking the serviceability of the starting and protective relay
Often the problem lies not in the engine itself, but in its starting system. The starting relay is responsible for supplying an impulse to the starting winding, and the thermal relay protects the motor from overloads. To check these elements, you need to disconnect the refrigerator from the power supply and remove the plastic casing at the back of the compressor.
Carefully remove the relay from the contact group of the compressor. Usually it is fixed with a bracket or simply put on three pins. Shake the device next to your ear: if you hear a ringing or knocking sound inside, it means the contacts are burnt or crumbled and the part needs to be replaced. This is the most common reason why compressor does not start, although electricity is supplied to it.
Also inspect the contacts for carbon deposits. If you see black spots or melted plastic, there is no point in cleaning such a part - its resource has been exhausted. For an accurate check, you can use a multimeter in continuity mode: the contacts should close and open when the relay position changes (for some types) or show resistance in the coil circuit.
How to remove the relay correctly?
Before removing the relay, take a photo of the location of the wires. Some models have a specific orientation (top-bottom), and if the relay is installed incorrectly, the compressor will burn out instantly.
Do not forget that the thermal relay may operate falsely if it is selected incorrectly or is deformed. However, most often it fails precisely after an attempt to start a jammed compressor, taking on a current shock.
Diagnostics of compressor windings with a multimeter
The most accurate way to check the electrical part of the engine is to measure the resistance of the windings. For this you will need a multimeter. Switch the device to resistance measurement mode (Ohms) to the limit of 200 Ohms or 2 kOhms. There are usually three terminals on the contact group of the compressor: two extreme and one common (or they can be arranged in a triangle).
It is necessary to ring all three contacts in pairs. You should get three resistance values. The sum of the resistances between pairs of contacts should be approximately equal to the resistance between the largest and smallest value. Typically, the resistance of the starting winding is higher (about 30-40 Ohms), and the working winding is lower (10-15 Ohms), and between the extreme contacts the sum gives the total resistance.
- 🔌 Normal: The device shows specific resistance values (for example, 12 Ohms, 35 Ohms, 47 Ohms), which indicates the integrity of the windings.
- 🚫 Break: If the device shows one (infinity) on any pair of contacts, it means that the winding is burned out or the wire inside the housing is broken.
- ⚡ Short circuit: If the resistance is close to zero on the working windings, an interturn short circuit has occurred and the motor will burn out immediately after switching on.
It is also critically important to check breakdown to the housing. Switch the multimeter to the resistance measurement mode at the maximum limit (MΩ) or to the diode test mode. Touch any contact with one probe, and touch the metal part of the compressor housing with the other (clean a small area of paint to be safe). The device should show infinity. Any resistance readings indicate that the insulation is broken, and such a refrigerator cannot be used.
☑️ Check with a multimeter
If the measurements showed normal values, but the motor does not start, the problem may be mechanical. However, electrical integrity is the first thing that eliminates the need for complex repairs.
Analysis of current strength and power consumption
If there are no visual defects, but the compressor hums and knocks out the machine or relay, it is worth measuring the starting current. For this purpose, special current clamps are used, which are placed on one of the power wires when the device is turned on. This method allows you to estimate how difficult it is for the motor to start.
Normally, the starting current can briefly exceed the operating current by 3-5 times, but then it should stabilize. If the current increases before the protection is triggered, this is a sure sign of an interturn short circuit or mechanical jamming of the piston group. You can also use a wattmeter plugged into the outlet to monitor actual energy consumption in real time.
| Parameter | Normal value | Fault symptom |
|---|---|---|
| Working winding resistance | 10 - 20 Ohm | 0 Ohm (Short circuit) or ∞ (Open) |
| Starting winding resistance | 20 - 50 Ohm | Significantly higher norms |
| Case resistance | ∞ (Infinity) | Any numerical value |
| Current consumption (operating) | 0.5 – 1.5 A | Increase to 3-5 A and higher |
Comparison of the obtained data with the passport values (if they are preserved on the nameplate) gives an accurate understanding of the condition electric motor. If the current is normal, but there is no cold, look for the problem in a freon leak or a clogged capillary tube, and not in the compressor.
⚠️ Attention: Measure the current only briefly. Prolonged operation of a faulty compressor under load can lead to melting of the wiring or fire.
Mechanical malfunctions and piston jamming
There are cases when the electrical part is completely intact: the windings are intact, there is no breakdown, the relay is working, but the compressor only hums and does not start. This indicates a mechanical problem. Most often, the piston group becomes jammed due to wear out of service life, moisture entering the system, or oil thickening.
In some cases, the so-called “wedging” method helps. Increased voltage is applied to the compressor contacts (through a special circuit with a capacitor) to create a powerful starting impulse that can break a jammed piston. However, this method is risky and requires experience, since you can completely finish off the motor or damage the wiring.
Another cause of mechanical noise (knocking, clanging) may be the destruction of the internal suspension of the compressor. The springs on which the motor is suspended inside the casing burst or jump off over time. In this case, the motor begins to hit the walls of the casing, producing a loud metallic clang. Repair in this case is not economically feasible.
Testing performance and pressure
If the engine starts, runs smoothly, but does not cool, it is necessary to check its performance. To do this, disconnect the capillary tube from the system and attach a hose with a pressure gauge to the compressor outlet. When turned on, a working unit should quickly create pressure.
Modern compressors must create an outlet pressure of at least 6 atmospheres (bar) in a short time. If the pressure gauge needle barely creeps or stands still, it means that the compressor “does not hold” pressure due to wear of the valves or piston group. In this case, replacing the unit is inevitable, since it is impossible to restore compression at home.
It is also worth checking whether the system is clogged. If the compressor hums very hard and the outlet pressure is low, there may be a blockage in the filter drier or capillary tube. In this case, the compressor itself may be in good working order, but work in extreme mode, which will quickly lead to its breakdown.
Frequently asked questions and answers (FAQ)
Is it possible to repair a refrigerator compressor yourself?
Replacing a compressor is theoretically possible, but requires special equipment: a vacuum pump, a pressure gauge station and skills in working with copper tubes. Self-replacement without evacuation of the system will lead to rapid failure of the new compressor due to moisture and air.
Why is the compressor hot to the touch?
The operating temperature of the compressor housing can reach 70-90 degrees Celsius, which is the norm for many models. However, if it is so hot that it is impossible to touch it, or it works non-stop, this is a sign of a malfunction of the thermostat, a freon leak, or problems with ventilation.
How much does it cost to replace a compressor?
The cost consists of the price of the unit itself (from 3 to 10 thousand rubles, depending on the model) and the cost of the work of a specialist. The total amount will also include materials: refrigerant, filter drier and solder. The exact price can only be found out after diagnosing a specific refrigerator model.
Is the inverter compressor humming?
Inverter compressors operate much quieter than usual, since they do not have sudden starts and stops. They smoothly regulate power. If the inverter refrigerator begins to hum or vibrate