Sudden stoppage of operation of the refrigerator or its inability to maintain the set temperature often indicates problems with the heart of the unit - the compressor. It is this unit that is responsible for circulating the refrigerant in the system, creating the necessary pressure to cool the chambers. When the motor stops starting, hums but does not turn on, or works with constant interruptions, the owner is faced with the question of the need for complex repairs or replacement of an expensive unit.
Before calling a technician or looking for a new refrigerator, it is worth carrying out the initial diagnostics yourself. Checking the compressor allows you to eliminate simpler and cheaper faults, such as failure of the start relay or thermostat. Understanding the principles of operation of an electric motor and knowledge of methods for measuring winding resistance will help you make an informed decision on further actions.
In this article we will analyze in detail the algorithm of actions, the necessary tools and the interpretation of the results obtained. You will learn to distinguish between the symptoms of mechanical jamming and electrical breakdown, and also understand in which cases repair is not economically feasible. Competent diagnostics is the first step to restoring the functionality of your household appliances.
Initial visual assessment and preparation for diagnostics
Any work with electrical appliances begins with ensuring safety. Before you start checking the compressor, you must completely turn off the power to the refrigerator by unplugging the plug from the socket. This is a critical rule and, if ignored, may result in electric shock or damage to the electronics.
After turning off the power, move the refrigerator away from the wall to allow access to the back wall. This is where the compressor is located, usually covered with a black metal casing. A visual inspection reveals obvious signs of malfunction that do not require the use of measuring instruments. Pay attention to the condition of the wires going to the motor and the absence of signs of burning or melting of the insulation.
⚠️ Attention: If you find traces of soot, the smell of burnt wiring or visible damage to the compressor housing, it is better not to carry out further diagnostics yourself. This may indicate a serious interturn short circuit or breakdown that requires professional intervention.
To carry out a quality diagnosis, you will need a basic set of tools. First of all, you need multimeter (tester) to measure the resistance of the windings. You may also need screwdrivers to remove the protective casing and terminal box, as well as pliers.
Be sure to prepare gloves, as the back of the refrigerator may be covered in a layer of dust or have sharp edges. Cleanliness and order in the workplace are the key to successful repairs and the absence of minor injuries.
Analysis of the operation of the motor by ear and external signs
A primary assessment of the condition of the compressor can be carried out by simply turning on the refrigerator and listening to its operation. The nature of the sound and the cyclical switching on allow an experienced technician to determine the type of malfunction even before taking measurements. A working unit should start with a characteristic click, operate smoothly and turn off when the set temperature is reached.
There are several typical scenarios for the behavior of a faulty compressor. If the engine hums but does not start, and after a few seconds there is a clicking sound and the hum stops, this often indicates a problem with the start relay or a jammed piston group. In the case when the compressor does not make any sounds at all when turned on, the problem may lie in a broken power circuit or a burnt-out winding.
Particular attention should be paid to the thermal regime. When the compressor heats up, but should not be hot. If, after a short cycle of operation, the motor housing becomes so hot that it cannot be touched, this is a signal of overload or mechanical friction inside.
The condition of the condenser (the grill at the back of the refrigerator) is also an important indicator. If the compressor operates continuously, and the grille remains cold or warm only at the very outlet of the motor, this may indicate a loss of performance or a freon leak, although the motor itself may be working properly.
Removing the protective casing and checking the start relay
For deeper diagnostics, it is necessary to gain access to the electrical contacts of the compressor. Remove the rear protective cover by unscrewing the mounting bolts. Underneath it you will see a compressor, to the bottom of which there is a plastic box attached - this is a starting relay and a thermal protector.
Carefully remove the relay from the contacts of the compressor. It is usually held in place by latches or a retaining bracket. Visually inspect the insides of the relay: the presence of blackening, melted plastic or a burning smell clearly indicates its malfunction. Often, it is a burnt-out relay that becomes the reason why the compressor does not start..
Checking the relay with a multimeter is carried out in continuity mode. The contacts must close and open in a certain position (depending on the design - vertical or horizontal). If the relay “rings” in any position or is completely silent, it must be replaced. This is an inexpensive part, and replacing it often solves the starting problem.
Is it possible to start a refrigerator without a relay?
Theoretically, you can start a motor without a starting relay by applying voltage directly to the starting winding through a button, but doing this is strictly not recommended without special skills. This is life-threatening and can completely kill the compressor.
After removing the relay, three contacts remain on the compressor body, forming a triangle. These are the winding terminals: starting, working and common. It is with them that we will have to work further. Before measuring, make sure that the contacts are dry and clean.
Testing the windings with a multimeter: step-by-step instructions
The most reliable way to check the electrical part of the compressor is to measure the resistance of the windings. To do this, switch the multimeter to resistance measurement mode (Ohm) with a limit of up to 200 Ohm or 2 kOhm. Before starting measurements, make sure that the probes are in good condition by connecting them to each other - the device should show zero or a value close to it.
You need to take measurements between the three contacts. Let's call them 1, 2 and 3. Write down the readings for each pair of contacts. Normal resistance values depend on the power and model of the engine, but usually they are within the following limits:
- 🔌 Resistance between the working and common contacts: from 10 to 30 Ohms.
- 🔌 Resistance between the starting and common contacts: from 20 to 50 Ohms.
- 🔌 Resistance between the working and starting contacts (sum of the previous two): from 30 to 80 Ohms.
It is important to understand the logic of measurements: the sum of the resistances of the two smaller values must equal the largest measured value. If this equality is observed, then the windings are intact. If the device shows infinity (one in the most significant digit), there is a winding break. If the resistance is close to zero, a short circuit has occurred.
☑️ Algorithm for checking the windings
Separately, it is worth checking that there is no breakdown in the case. To do this, one multimeter probe is applied to any of the contacts, and the second is applied to a copper tube or an unpainted part of the compressor housing. The device should show infinity. Any resistance indicates that the insulation is broken and the motor is dangerous for operation.
⚠️ Attention: Even if the winding resistance is normal, this does not guarantee complete serviceability of the compressor. Mechanical defects (piston scuffing, valve wear) cannot be determined with a multimeter.
Table of typical values and interpretation of results
For ease of interpretation of the data obtained, we present a table with possible measurement results and their meaning. This will help you make a diagnosis faster.
| Multimeter readings | Between which contacts | Probable cause | Actions |
|---|---|---|---|
| Infinity (1) | Any pair | Winding break | Replacing the compressor |
| Close to 0 Ohm | Any pair | Short circuit | Replacement of the compressor |
| Normal (the amount is the same) | All pairs | Electrics are OK | Check mechanics and freon |
| Yes resistance | Contact - Housing | Breakthrough to housing | Urgent replacement (dangerous!) |
| Values are very different | From passport data | Interturn short circuit | Replacing the compressor |
If the measurements showed normal values, but the refrigerator still does not work, the problem may be hidden deeper. For example, in turn-to-turn short circuit, which changes the resistance slightly, but leads to overheating and tripping of the thermal relay. It is also worth checking the thermostat and defrost sensors if the refrigerator model is No Frost.
In some cases, the resistance may “float” when heated. A cold compressor may sound fine, but when heated, it may break. This is a characteristic sign of aging winding insulation.
Mechanical check: assessment of pressure and condition of the piston
When the electrical part has been checked and does not raise any questions, it is the turn to check the mechanical component. The most common mechanical failure is loss of compression. This means that the motor is spinning, humming, but does not create the necessary pressure for freon circulation.
You can check the presence of pressure in a simple way. A pressure gauge is installed on the compressor outlet pipe (the hot one). When a working unit is turned on, the pressure gauge needle should rise quickly, indicating the discharge pressure. If the pressure does not increase or increases very slowly, it means that the valves inside the compressor are burnt out or the piston rings are stuck.
Another indirect sign of a mechanical malfunction is a characteristic sound. If you hear a metallic clanging, knocking or grinding sound when starting up, this indicates destruction of internal parts. In such cases compressor repair is impossible, only replacement of the entire unit is required.
Why can’t you open the compressor?
The compressor is a sealed welded unit. Opening it at home is impossible without special equipment for welding and vacuuming. Even if you fix the mechanics, you won’t be able to solder the case back while maintaining tightness.
It’s also worth checking the condition of the suction tube. If it is pinched or clogged with an oil plug, the compressor will run idle. However, most often the problem lies precisely in the wear of the cylinder-piston group after many years of operation.
Frequently asked questions and final recommendations
To summarize, we can say that compressor diagnostics is a process of elimination. First we check the power supply and relay, then the electrical resistance, and only then we draw conclusions about the mechanics. If you have gone through all the steps and are convinced that the motor is faulty, you will be faced with a choice: replacing the compressor or buying a new refrigerator.
It is worth considering that replacing a compressor is an expensive procedure that requires a skilled technician, the presence of a vacuum pump, freon and soldering tools. In old refrigerators, the cost of such repairs can be up to 70% of the price of new equipment.
If diagnostics show that the compressor is working, but there is no cold, look for the cause in a freon leak or a clogged capillary system. These problems also require calling a specialist, but do not involve replacing the motor itself.
Is it possible to check the compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without instruments. However, you can try to supply 220V voltage directly through a working starting relay (being careful!). If the engine starts and hums smoothly, the electrics are intact. If the plugs blow out or smoke comes out, the engine is burnt out. This method is dangerous and does not provide accurate data on resistance.
Why is the compressor hot, but the refrigerator does not freeze?
This is a classic sign of a refrigerant leak or a malfunction of the compressor itself (loss of compression). The engine idles, overheats, but does not pump freon through the system. Also, the cause may be a clogged capillary tube.
How long should the compressor operate normally?
The operating time depends on the load of the refrigerator, the room temperature and the model. Typically the work cycle is 10-20 minutes, followed by a pause of the same duration. If the motor runs without stopping for hours, this is a sign of a thermostat malfunction, freon leakage or compressor wear.
Is it possible to use a used compressor for replacement?
You can use a compressor removed from another refrigerator, but only if you are sure of its origin and condition. "Pigs in a poke" from disassemblies often have exhausted resource. It is better to install a new original or high-quality analogue.