A sudden stop of refrigeration equipment often takes you by surprise, and the first suspicious sign is the absence characteristic hum of a running engine. When it starts to get warm inside the chamber, and the light is on, but the unit is silent, a natural need arises to find out whether compressor the problem lies in the electronics. Self-diagnosis allows you to understand the scale of the disaster and decide whether to call a technician or try to fix the problem on your own.
However, before you grab the tools, it is important to understand that refrigeration unit is a complex system where the engine is only one of the elements of the chain. Silence does not always mean a breakdown of the motor itself; sometimes the starting relay, thermostat or a simple lack of voltage in the network is to blame. The correct sequence of actions will help to avoid unnecessary expenses and errors when searching for a defect.
In this article we will analyze in detail the algorithm for checking the performance of the engine, consider methods of using a multimeter and describe indirect signs indicating a malfunction. You will learn to distinguish a burnt winding from a jammed piston and understand when repairs no longer make economic sense. Safety when working with electrical appliances is a paramount rule that cannot be ignored for a second.
⚠️ Attention: Any work on diagnosing the internal components of the refrigerator should be carried out only after completely disconnecting the device from the electrical network. Residual voltage in capacitors can be life-threatening.
Primary visual diagnostics and sound analysis
The check should always begin with an external inspection and listening to a running (or trying to start) unit. If you hear a quiet click, followed by a buzzing sound that lasts a few seconds, and then another click and silence, this is a classic symptom of a starting attempt. The engine is trying to turn over, but something is preventing it from gaining operating speed. In such a situation starting relay turns off the power to prevent overheating of the windings.
Pay attention to the temperature of the motor housing. If, after several starting attempts, the metal casing of the engine becomes hot, this may indicate an inter-turn short circuit or a mechanical wedge in the piston group. Under normal conditions, a running compressor should be warm, but not scalding. Also inspect the condenser tubes (usually the grille on the back): if one of them is hot and the other is cold when the motor is running, there is freon circulating, and the problem may not be in the motor.
Sometimes the problem lies not in the motor itself, but in the control system. Modern models with an electronic module can block the compressor from starting if the temperature sensors are faulty. Therefore, if there are visually no traces of carbon deposits or melted insulation on the engine, do not rush to write it off. Checking the integrity of the wires going to the terminal box is also a mandatory step in the initial diagnosis.
Checking the starting relay and thermostat
Before testing the engine itself, it is necessary to exclude malfunction of the elements that supply current to it. The start relay is a small plastic block that fits over the contacts of the compressor. It is this that supplies the impulse to the starting winding to start the rotor. If the relay is faulty, the engine will physically not be able to start, even if its windings are intact. Remove the relay, carefully disconnecting it from the contacts, and shake: if you hear the ringing of broken parts inside, the element requires replacement.
The thermostat (or temperature sensor in No Frost models) opens the compressor power circuit when the set temperature is reached in the chamber. To check it, you can short-circuit the wires coming from the thermostat, bypassing the regulator itself. If after this procedure the refrigerator “came to life” and the motor began to hum, it means that the problem was in the sensor and the motor is working. This is a simple but effective way to narrow the search.
It is also important to check the condition of the contacts at the junction of the relay and the motor. Oxidation or burning of contacts creates high resistance, which is why the current simply does not reach the windings. Cleaning the contacts with fine sandpaper sometimes allows you to revive an old device without purchasing new parts. If everything is visually clear, we move on to more accurate instrumental measurements.
Diagnostics of motor windings with a multimeter
The most reliable way to find out the condition of the motor is to ring its windings using a multimeter. To do this, you need to remove the back cover, gain access to the compressor contact group and remove the start relay. There are usually three contacts on the terminal block: common, starting and working. Switch the multimeter to resistance measurement mode (Ohm) to a limit of 200 Ohm.
First, check for a “breakdown” in the case. Touch one probe to any contact and the other to the copper tube or unpainted part of the engine housing. The device should show infinity (one in the most significant digit). If you see any resistance values, it means that the insulation is broken, and operating such a motor is strictly prohibited due to the risk of electric shock.
☑️ Winding testing algorithm
Next we measure the resistance between the contacts themselves. Normal values may vary depending on the power of the motor, but usually range from 10 to 30 ohms between the common and working contacts, and a little more between the common and starting contacts. The sum of the resistances of the starting and working windings must be equal to the resistance between the starting and working contacts. If the device shows zero, there is a short circuit, if infinity, there is an open circuit. In both cases, the engine is considered faulty.
Table of normal resistance indicators
For ease of comparison of the obtained data, you can use the reference table. Please remember that the values may vary slightly depending on the manufacturer and model of the compressor (for example, Atlant, Indesit or LG may have different characteristics). However, the order of the numbers is usually maintained within certain limits.
| Measurement type | Normal value (Ohm) | Fault | Action |
|---|---|---|---|
| General - Working | 10 - 25 Ohm | 0 Ohm or ∞ | Replacing the compressor |
| General - Starting | 20 - 40 Ohm | 0 Ohm ∞ | Replacement of the compressor |
| Contact - Housing | ∞ (Infinity) | Any number | Urgent disposal |
| Start relay | Depends on the model | No ringing/break | Replacing the relay |
If your measurements are radically different from the tabulated data, for example, the resistance of one of the windings is several times less or more another, this indicates a turn short circuit. In this case, the engine will get very hot and consume increased current, which will quickly lead to burning of the wiring in the apartment or knocking out plugs.
Checking the current strength and mechanical wedge
If the electrical tests showed normal, but the engine still does not start or the machine immediately knocks out, the problem may be mechanical. This is the so-called “wedge” of the piston group, when the oil has thickened or the parts have worn out and become stuck. To check the starting current strength, special current clamps are used, which are placed on the power cord when the device is turned on. If the current at the time of start-up exceeds the nominal value by 3-4 times and does not drop, the motor is jammed.
There is a popular but risky method of “wedging” by applying increased voltage or mechanical action, but in modern conditions this rarely gives long-term results. An attempt to start a jammed compressor can lead to depressurization of the housing and the release of oil through the process pipe. If you do not have experience working with vacuum pumps and refilling with freon, it is better not experiment.
Is it possible to restore a jammed compressor?
In some cases, adding a special additive or short-term supply of 380V voltage (for three-phase motors in a sprocket) helps, but such operations are low and require professional equipment.
It is also worth checking the condition of the oil. If, when opening the system (which is not recommended to do without skills), the oil turns out to be black and has an acidic smell, it means that there was an insulation breakdown inside the engine and the windings burned out. The acid contained in such oil corrodes the varnish insulation of wires throughout the entire system, so simply replacing the motor without flushing the circuit will lead to repeated failure in a short time.
Specifics of diagnostics of inverter compressors
Owners of modern refrigerators with the system No Frost and inverter control you should know: it is almost impossible to check such a motor with a conventional multimeter for performance. Inverter motors do not have a classic starting relay, and they are controlled by a complex electronic unit. Continuity testing of the windings will only show the absence of obvious short circuits, but will not indicate the condition of the electronic components inside.
Diagnostics of an inverter compressor requires a special tester that simulates the operation of the control module. Without such equipment, one can only state the fact that there is no launch. Often in such models the problem lies not in the motor itself, but in the control board, which fails due to power surges in the network. Replacing an inverter compressor is an expensive procedure that requires resoldering the tubes and evacuating the system.
⚠️ Attention: Inverter compressors are sensitive to the quality of installation. The ingress of a microscopic amount of moisture or air during replacement can damage the new expensive unit.