A sudden stop of the refrigerator or, conversely, its continuous hum without cooling the food is always a signal of a serious problem. Most often, owners of household appliances blame the thermostat or a freon leak, but the real culprit of the malfunction is often the heart of the unit - compressor. It is this unit that is responsible for the circulation of the refrigerant, and if it fails, the refrigerator turns into an ordinary cabinet.
Before calling a technician or buying a new unit, you should try to diagnose the condition of the motor yourself. This will save a significant amount if the problem turns out to be in the starting relay, or avoid purchasing faulty equipment second-hand. In this article, we will look at how to check the functionality of a refrigerator compressor using simple tools and careful analysis of symptoms.
Diagnostics require compliance with safety precautions, since you will be working with electric current and potentially dangerous gases. However, if you act carefully and consistently, you can get an accurate answer about the condition of the engine in 30-40 minutes. Indesit, Atlant, Bosch or any other brand - the principles of checking the electromechanical part are similar for most models.
Primary visual and auditory diagnostics
Any in-depth check begins with a superficial inspection, which often allows identify obvious defects without disassembling the unit. Plug in the refrigerator and listen: if you hear a quiet hum that ends abruptly with a click and then repeats, this is a classic sign that the engine is trying to start but cannot. This cycle can be repeated endlessly, indicating problems with the trigger mechanism or jamming of the piston group.
Pay attention to the temperature of the compressor housing itself. If the motor is hot, almost burns your hand, but the refrigerator does not cool, this may indicate an interturn short circuit of the windings or thermal breakdown. A normally operating compressor should be warm, but not hot. Also inspect the rear wall for oily stains: oil leakage often accompanies mechanical destruction of the shaft seals.
- 🔊 Sound anomalies: metallic clanging, strong vibrational hum or complete absence of sound when turned on.
- 🔥 Temperature mode: excessive heating of the motor housing or, on the contrary, absolute coldness when the network is working.
- 💡 Indication: blinking of a light bulb inside the chamber or light indicators on the control panel (for modern models).
⚠️ Attention: If, when turning on the refrigerator, the circuit breaker (plugs) in electrical panel, stop attempting to start immediately. This is a sure sign of a short circuit in the compressor circuit, and further switching on can lead to a fire.
It is important to distinguish the noise of the compressor from the noise of the fan (in No Frost systems) or the gurgling of freon. The motor emits low-frequency vibration, which is transmitted to the body of the entire refrigerator. If you place your hand on the side wall and feel a rhythmic trembling that coincides with a hum, then the mechanical part is most likely intact, and the problem may lie in the electrics or heat dissipation system.
Checking the starting relay and contacts
Before “climbing” into the motor itself, it is necessary to rule out a malfunction start relay. This small black or white plastic block, placed over the compressor contacts, is responsible for starting the engine and protecting it from overloads. Statistics show that in 40% of cases, a “burnt out compressor” turns out to be serviceable, and the problem lies precisely in this cheap element.
To check, unplug the refrigerator, remove the rear protective panel and dismantle the relay. Carefully disconnect the wires and inspect the inside of the relay for burning, melted plastic, or a burning smell. If a black coating is visible inside or there is a smell of burnt plastic, the relay definitely needs to be replaced. You can check a mechanical relay by shaking it near your ear: if you hear the ringing of parts falling apart, the device is faulty.
How does a starting relay work?
Inside the relay there is a coil and a movable core. When voltage is applied, the coil creates a magnetic field that draws in the core and closes the starting winding. When the engine picks up speed, the current drops and the core, under the influence of gravity, opens the circuit. If this mechanism jams, the motor will not start.
Clean the contacts on the compressor itself if they are oxidized. Use fine sandpaper or rubbing alcohol, but be careful not to damage the leads. After cleaning and installing a new (or known good) relay, try turning on the unit. If the motor starts and runs smoothly, the problem is solved.
- 🔌 Integrity of the housing: no cracks or signs of overheating on the plastic casing of the relay.
- 🧹 Cleanliness of contacts: no oxides and carbon deposits on the compressor pins and in the relay mating part.
- 🔨 Mechanical test: no rattling of internal parts when shaking the relay.
If replacing the relay did not help, and the symptoms persist, you will have to move on to a more complex procedure - checking the continuity of the motor windings with a multimeter. This will require removing the relay and, possibly, dismantling the casing covering the electrical part of the motor.
Diagnostics of windings with a multimeter
To carry out this operation, you will need a digital multimeter configured to measure resistance (limit 200 Ohms or 2 kOhms). There are three contacts on the compressor housing, forming a triangle. Usually they are marked with letters, but if there are no markings, you need to determine them experimentally. Two contacts are the working and starting windings, and the third is common.
Ring each pair of contacts with each other. The resistance between the common and working terminals should be minimal, between the common and starting terminals - slightly higher, and between the working and starting terminals - the sum of the two previous values. If the device shows one (infinity) on any pair, it means that the winding is in break, and the compressor must be replaced. If the resistance is close to zero, there is short circuit.
| Pair of contacts | Normal resistance (Ohm) | Diagnosis of deviation |
|---|---|---|
| General - Working | 10 - 30 Ohm | Open or short circuit |
| General - Starting | 20 - 50 Ohm | Starting fault windings |
| Working - Starting | Sum of the two above | Measurement error or breakdown |
| Any contact - Housing | Infinity (∞) | Breakthrough to the body (dangerous!) |
Pay special attention to checking for breakdown to the body. Press one multimeter probe to any contact, and the second to a place on the metal body of the compressor that has been cleared of paint. The device should show infinity. If there is at least some resistance, it means that the insulation is broken, and operating such a refrigerator is strictly prohibited due to the risk of electric shock.
The numbers may vary depending on the power and engine model. For low-power compressors used in compact refrigerators, the values may be higher, for industrial ones - lower. The main thing here is the ratio of values and the absence of a ground fault.
Checking for an interturn short circuit
The most difficult defect to diagnose is an interturn short circuit. In this case, the winding is intact, the contacts do not ring into the housing, but some of the turns inside the coil are closed. In this case, the engine can hum, heat up and even start, but consume a current significantly higher than the rated one, quickly burning out completely.
It is almost impossible to identify this malfunction with a multimeter in ohmmeter mode, since the change in resistance will be minimal and may fall within the tolerance. For accurate diagnosis, current measurement will be required. For this purpose, current clamps are used, which are placed on one of the power wires when the refrigerator is turned on.
⚠️ Attention: Current measurement is carried out under a voltage of 220V! Be extremely careful not to touch exposed wires with your hands. If you are not confident in your skills in working with the electrical network, it is better to skip this step.
Compare the data obtained with the rated current indicated on the compressor nameplate (for example, 1.2 A). If the actual current exceeds the nominal current by 20-30% or more, and the refrigerator does not cool, this is a sure sign of an interturn short circuit. Such a motor will not last long, and its resource is exhausted.
Also an indirect sign can be the behavior of the refrigerator: it turns on, runs for 5-10 minutes, gets very hot and is turned off by a thermal relay without ever reaching the desired temperature. Under normal conditions, the operating cycle should be longer and the heating should be moderate.
Mechanical check: piston jamming
If the electrical part is in order (the windings are intact, there is no breakdown, the current is normal), but the motor does not start or is humming, there is a high probability of mechanical jamming. The piston group could wear out, or the compressor could go into “hydraulic shock” due to liquid freon getting into the cylinder.
There is a risky, but sometimes effective method of “swinging”. The compressor contacts (bypassing the standard relay) supply voltage directly to the working winding for a short time (2-3 seconds). If the motor catches, it may turn over and come out of the wedge. However, this method requires special skills, the presence of a starting capacitor and an understanding of the connection diagram, otherwise you can easily finish off a working motor or get an electric shock.
- 🛑 Sign of jamming: a powerful beep when trying to start and instant shutdown by thermal protection.
- 🔨 Tapping method: sometimes light blows on the body with a rubber mallet when the compressor is on, they help move jammed parts.
- 🔄 Reverse scrolling: in rare cases, a short-term supply of voltage to the starting winding can turn the shaft and remove the wedge.
If The compressor is jammed tightly, no amount of dancing with a tambourine will help. There are irreversible changes inside: scuffing on the cylinders, destruction of the connecting rod or valves. The only way out is to replace the unit with a new one or a contract one.
☑️ Checklist before replacing the compressor
Specifics of inverter compressors
Modern refrigerators are increasingly are equipped with inverter compressors, which operate according to a fundamentally different scheme. They do not have a classic start relay, and the engine is controlled by an electronic unit. It is possible to ring the windings of such a motor with a conventional multimeter, but it is extremely difficult to carry out a full performance check without a special tester or connection to a native control unit.
The windings of inverter motors often have very low resistance, and the spread of values between phases can be minimal. In addition, in such systems, what is more important is not the integrity of the windings, but the serviceability of the rotor position sensors built into the motor. If the electronics sees a sensor error, it simply will not start the compressor, even if it is completely mechanically functional.
To diagnose inverter systems, it is often necessary to connect a pressure gauge station to check the discharge pressure. If the motor is spinning (this can be heard or felt by vibration), but there is no pressure in the system, then the problem is not in the electrics of the motor, but in its mechanical part (valves) or in the absence of freon.
⚠️ Attention: Inverter compressors are sensitive to voltage surges. Before replacing such a unit, be sure to check the quality of the electrical network in your home, otherwise the new expensive motor will also fail.
Owners of equipment with linear compressors (often found in LG) should know that they make characteristic clicking sounds during operation, which is the norm, and not a sign of failure. Diagnostics of linear motors also requires taking into account the specifics of their piston stroke.
When a compressor replacement is necessary
To summarize: if you find a break or short circuit in the windings, a breakdown to the housing or a confirmed inter-turn short circuit, the compressor must be replaced. Repairing an old motor at home is impossible, as it requires sealed rewinding in a factory, which is not economically feasible.
Replacement is also inevitable if internal components are mechanically damaged. A characteristic metallic knock and lack of compression (checking for a break in the air stream at the outlet pipe when turned on for a short time) indicate that the piston group is dead. Operating such a refrigerator is useless.
When purchasing a new compressor, pay attention not only to the dimensions, but also to the power, refrigerant (R134a, R600a) and oil type. An incorrectly selected motor can quickly fail or not provide the required performance. The model must be compatible with your type of refrigerator.
Remember that the service life of the compressor directly depends on operating conditions: the cleanliness of the condenser, the correct temperature in the room and voltage stability. Regular defrosting and cleaning dust from the back of the refrigerator will prolong the life of the new unit.
Is it possible to use a compressor from another refrigerator?
Theoretically, yes, if the power and type of refrigerant match. However, it is better to select an exact analogue by catalog number in order to avoid problems with the compatibility of the oil-freon system and control electronics.
Frequently asked questions (FAQ)
Is it possible to check the compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without instruments. However, the malfunction will be indirectly indicated by the nature of the sound (humming with clicks), the heating of the case and the behavior of the refrigerator (it does not freeze when the fan is running). A visual inspection of the relay and contacts also provides a lot of information.
How much does it cost to replace a compressor on average?
The price consists of the cost of the unit itself (from 3 to 10 thousand rubles, depending on the model) and the work of a specialist (from 2 to 5 thousand rubles). You also need to take into account the cost of refilling with freon and consumables.
Why did the new compressor immediately burn out?
Frequent reasons: poor-quality soldering (solder getting into the system), lack of evacuation (remaining moisture and air), use of the wrong oil or power surges in the network immediately after installation.
The compressor hums, but does not start - what to do?
Most likely, the start relay is faulty or the piston group is jammed. Start by replacing the relay - this is the cheapest and easiest option. If this does not help, diagnostics of the windings and mechanics will be required.
Is it dangerous to touch a running compressor?
You can touch the housing of a running compressor, it may be hot, but it should not burn. However, touching electrical contacts and wires while the refrigerator is plugged in is deadly. Always turn off the appliance before any intervention.