A sudden cessation of cold in the chamber or, conversely, continuous operation of the unit is always stressful for the owner of household appliances. Compressor is the heart of the refrigeration system, and it is from here that the search for the cause of the breakdown begins, when food begins to deteriorate. Understanding the principles of operation of this unit allows you not only to save on calling a technician, but also to accurately diagnose the problem, avoiding unnecessary expenses on replacing serviceable parts.
Before grabbing the tools, it is necessary to conduct an initial visual and auditory assessment of the condition of the equipment. Often, signs of a malfunction motor-compressor are obvious even without disassembly: the absence of a characteristic hum, silence when plugged into the network, or, conversely, a loud knocking and humming. It is important to distinguish between situations when the refrigerator has simply defrosted due to a power surge, and cases when a serious repair or replacement of the unit is required.
In this article we will analyze in detail the algorithm of actions for checking the performance of the compressor using various methods. You will learn how to use a multimeter to measure winding resistance, how to estimate system pressure, and what to look for during an external inspection. A competent diagnostics at the initial stage will help you make the right decision about the future fate of your refrigerator.
Primary diagnostics without tools
You should always start checking with the simplest thing - analyzing sounds and appearance. A working compressor emits a uniform, monotonous hum, which is periodically interrupted when the thermostat opens the circuit. If you hear that the motor is humming, but the refrigerator is not cooling, or it clicks and immediately goes silent, this indicates serious problems with the start or mechanical part.
Pay attention to the temperature regime of the rear wall of the unit. Normally, the condenser (grid at the back) should be warm or hot, and the evaporator inside should be uniformly cold. If compressor works continuously, but heat exchange does not occur, the system may be sealed or a refrigerant leak has occurred. The smell is also an important indicator: the appearance of burning indicates overheating of the windings or melting of the insulation.
⚠️ Attention: If you smell burning wiring or see sparking in the connection area, immediately disconnect the refrigerator from the network. Continued operation in this condition may result in fire or electric shock.
For a more accurate understanding of the condition, listen to the startup pattern. A normal start is accompanied by a quiet click from the start relay and an increasing hum. If a loud metallic clang, knock or crack is heard, this is a sure sign that the piston is damaged or the piston is jammed. In such cases, further attempts to turn on can finally finish off the unit. internal mechanisms damaged or the piston is jammed. In such cases, further attempts to turn on may finally finish off the unit.
Checking the electrical circuit and starting relay
If a visual inspection does not give a clear answer, you need to proceed to checking the electrical part. The first step should always be to completely unplug the appliance. Only then can you remove the back cover at the bottom of the refrigerator where the compressor is located. Here we are primarily interested in starting relay and the protective thermal relay, which are placed on the motor contacts.
Carefully remove the plastic relay box. Often inside you can find traces of soot or melted contacts. If the relay makes a rattling sound when shaken, then its internal contacts are damaged and it needs to be replaced. However, even external integrity does not guarantee serviceability, so the best solution would be to check the elements with a tester or install a known working relay for an experiment.
- 🔌 Inspect the contacts: Check the terminals for oxidation and the reliability of the connection to the wires.
- 🌡️ Thermal relay: Make sure that the bimetallic plate is not deformed from overheating.
- 🔨 Mechanical integrity: The relay housing should not have cracks or signs of breakdown.
Often the cause of failure is not the motor itself, but the starting system. If after replacing the relay the refrigerator starts working normally, then the problem has been solved. If the motor still does not start or the machine in the panel knocks out, it is necessary to check the resistance of the windings itself compressor. This requires more accurate measurements and the use of a multimeter.
Diagnostics of windings with a multimeter
The most reliable method of checking an electric motor is to measure the resistance of its windings. To do this, you will need a multimeter switched to resistance measurement mode (Ohms) to a limit of 200 Ohms. There are usually three contacts on the compressor housing: two for the working and starting windings and one common. The connection diagram can often be found in the technical documentation or on a sticker.
The measurement process involves testing pairs of contacts. First, we measure the resistance between the common contact and the contact of the working winding, then between the common and the starting winding. Finally, we measure the resistance between the starting and working windings. The sum of the first two values should approximately equal the third. If the multimeter shows one (infinity), it means in the winding break has occurred. If the resistance is close to zero, a turn-to-turn short circuit.
Normal resistance values (approximate):Working winding: 10-30 Ohm
Start winding: 20-50 Ohm
Between windings: sum of values
Particular attention should be paid to checking for breakdown on the housing. Switch the multimeter to dial mode (with sound) or resistance measurement to the maximum limit. Touch any contact with one probe and touch a cleaned area on the compressor housing with the other (for example, around the tubes or on mounting bolts). The device should not respond. If a squeak is heard or the arrow deviates, the winding is shorted to the housing, which makes operation dangerous.
☑️ Algorithm for testing with a multimeter
Analysis of pressure and tightness of the system
The electrical health of the motor is only half the battle. The compressor may sound great with the tester, but not create the required pressure in the system. To check this parameter, a pressure gauge station is required. The technician connects the hose to the service fitting (if there is one) or cuts into the process tube at the discharge.
When a working unit is turned on, the pressure gauge needle should rise quickly. For household refrigerators, a discharge pressure of around 6-9 atmospheres is considered normal (depending on the type of refrigerant: R134a or R600a). If the pressure grows extremely slowly or does not rise above 2-3 atmospheres, this indicates wear of the piston group or valves. In this case, the compressor is not able to circulate freon in the required volume.
| Parameter | Normal value | Malfunction symptom |
|---|---|---|
| Discharge pressure | 6 - 9 atm | Low pressure (valve wear) |
| Current consumption | 0.8 - 1.2 A | High current (wedge) or low (idling) |
| Case temperature | 70 - 90 °C | Overheating (>100 °C) or cold motor |
| Winding resistance | 10 - 80 Ohm | Open or short circuit |
| Operating time | Cyclic | Works without stopping |
It is also important to check the system for leaks. If the compressor pumps normally, but there is no cold, there may be a leak in the circuit. Professionals use leak detectors or the method of soaping connections. It is difficult to do this on your own, but you can pay attention to oily stains at the junction of the tubes or on the floor under the refrigerator - oil only comes out along with the gas through the depressurization point.
Why is it important to know the type of refrigerant?
The type of refrigerant (R134a or isobutane R600a) affects the operating pressure and type of oil. By mixing up the brand when refueling or using the wrong oil, you can damage a new compressor in a matter of hours.
Assessing the level of noise and vibration
The sound of a refrigerator operating can tell an experienced diagnostician a lot. The normal operating sound is a smooth hum. However, there are specific noises that indicate specific defects. For example, a loud knocking sound during startup often indicates broken piston liners or pins.
If you hear gurgling or fluid pouring immediately after stopping the engine, this may be a sign of liquid refrigerant entering the compressor cylinder (hydraulic hammer). This is dangerous and requires checking the thermostat and the amount of freon charged. A constant high-pitched whistle may indicate problems with valves or oil leakage.
- 🔊 Metallic clanging: Destruction of internal mechanical components.
- 📉 Low humming: Starting attempt with a stuck rotor.
- 💨 Hissing: Gas leak in the area of the compressor or pipes.
Vibration is also an important diagnostic parameter. Light vibration of the cabinet is acceptable, but if the entire refrigerator shakes or the compressor “beats” the cabinet, check the shock-absorbing rubber pads. Sometimes excessive vibration is caused not by the motor, but by improper installation of the unit itself on the floor.
When a compressor replacement is required
There are a number of situations when repairs become economically impractical or technically impossible. If the diagnostics showed an interturn short circuit in the windings or a breakdown on the housing, the compressor must only be disposed of. It is impossible to restore the insulation inside the sealed casing.
Replacement is also necessary in case of mechanical jamming, when the motor hums, the current consumption increases sharply to maximum values, but the shaft does not rotate. Attempts to “unwedge” such units by applying increased voltage often give only a short-term effect and can lead to final burnout of the wiring.
⚠️ Attention: Replacing a compressor yourself requires special tools (burner, vacuum pump, pressure gauges) and skills in working with open fire and gas. If you are not confident in your abilities, it is better to entrust this work to professionals so as not to break the tightness of the circuit.
When deciding on a replacement, consider the age of the refrigerator. If the equipment is more than 10-12 years old, the cost of a new compressor and installation work can be a significant part of the cost of the new device. In such cases, it is sometimes more profitable to purchase a new refrigerator with modern energy efficiency and a warranty.
Frequently asked questions (FAQ)
Is it possible to check a compressor without a multimeter?
Completely - no. You can only indirectly evaluate its performance by sound, heating and lack of cold. However, it is impossible to determine a winding break or a short circuit to the housing without a measuring device. For accurate diagnostics, a multimeter is needed.
Why does the compressor turn on and then immediately turn off?
This can happen for several reasons: a malfunction of the start relay, a jammed motor, a refrigerant leak (the protection is activated) or a broken thermostat. A sequential check of all components is required.
Is it dangerous to touch the compressor with your hands during operation?
Yes, it is dangerous. During operation, the compressor housing heats up to 70-90 degrees or higher, which can cause burns. In addition, there is a risk of electric shock if the insulation is broken. Carry out all checks only with the device turned off.
How much does it cost to replace a compressor?
The price consists of the cost of the unit itself (which depends on the brand and power) and the cost of work. On average, this can range from 30% to 60% of the cost of a new refrigerator, which is why preliminary diagnostics are so important.