Malfunction of the refrigeration unit often takes you by surprise, and the first suspicious symptom is silence where there should be a working hum of the engine. If the light inside the chamber is on, but the cold is not pumped, and it compressor is silent or makes only short clicks, this is a sure sign of problems in the electrical circuit or mechanical part of the engine. In such a situation, the owner needs to carry out initial diagnostics to understand whether complex repairs are required or whether a simple replacement of the starting relay is sufficient.
Independent testing and an attempt to start the engine directly allows you to exclude faulty auxiliary elements, such as a thermostat or control unit, from the equation. However, it is worth understanding that working with high voltage and refrigerants requires extreme caution and compliance with safety precautions. Any carelessness when working with start-up protection relay or motor windings can lead to electric shock or final failure of the unit.
In this article we will analyze in detail the algorithm of actions for checking the serviceability of the motor, consider methods for measuring winding resistance with a multimeter and describe the direct start procedure. You will learn how to correctly interpret the instrument readings and what precautions should be taken before starting work. Remember that directly starting a working compressor that is jammed due to lack of oil can completely destroy the mechanical part of the unit.
Primary visual diagnostics and preparation
Before taking up the tools, It is necessary to conduct a thorough external inspection of the unit and assess the nature of the malfunction. Often the problem lies not in the motor itself, but in a simple open circuit or blown fuse. Unplug the refrigerator and carefully inspect the back wall where the compressor compartment is located. Look for traces of burning, melted insulation or oil leaks, which may indicate a breakdown or depressurization of the system.
Remove the protective cover covering the compressor and start relay. In modern models Indesit or Atlant this is usually a plastic casing secured with latches or screws. Carefully remove the relay that is attached to the contact pins of the compressor. Visually assess the condition of the contacts: the presence of oxides, carbon deposits or deformation of the relay body indicates that this particular element could have caused the engine to stop.
Check the integrity of the suitable wires. If there is no visual damage, you can proceed to a more in-depth diagnosis using measuring instruments. It is important to ensure that the capacitor, if present in the circuit, is not swollen or cracked.
⚠️ Attention: Before starting any work on dismantling the elements, make sure that the power cord is unplugged from the outlet. Residual voltage in the capacitors can be dangerous; let the equipment stand unplugged for several minutes.
☑️ Preparation for diagnostics
Instrumental check of the windings with a multimeter
The most accurate way to determine the condition of the electrical part of the engine is to test the windings using a multimeter. Most compressors have a diagram or pin marking on the body, but often the pins are lettered or arranged in a specific geometric pattern. Typically, three contacts form a triangle: two upper and one lower, or are located in a row.
Switch the multimeter to the resistance measurement mode (Ohms) to the 2 kOhm limit. Sequentially measure the resistance between each pair of contacts. You need to find three values: the resistance of the starting winding, the working winding and the total resistance. For a working engine, the sum of the resistances of the two smaller values should be equal to the largest value.
If the device shows one (infinity) on any of the pairs of contacts, this indicates a winding break. In this case, the motor must be replaced, since rewinding at home is impossible and economically infeasible. If the resistance is close to zero, it means that an interturn short circuit has occurred, which is also a fatal malfunction.
The table below gives approximate resistance values for various types of compressors, however, the exact data depends on the model and manufacturer:
| Winding type | Resistance range (Ohm) | Nature of malfunction |
|---|---|---|
| Working winding | 10 - 25 Ohm | Open or short circuit |
| Starting winding | 20 - 40 Ohm | Open or short circuit |
| Total resistance | The sum of the two is higher | Circuit violation |
| Case (mass) | Infinity | Breakthrough to the body |
Pay special attention to checking the breakdown to the body. Press one multimeter probe to any of the contacts, and touch the other to the copper tube or a cleaned area on the compressor housing. The device should show infinity. The appearance of any resistance values indicates that insulation is broken and operating such a unit is deadly.
Diagnostics starting and thermal relay
Often the compressor itself is working, but cannot start due to a faulty starting relay. This small block is responsible for sending a pulse to the starting winding and subsequently disconnecting it from the network. Inside the relay there is a coil and a movable core, which, under the influence of current, moves and closes the contacts. Over time, the contacts may burn out and the coil may lose its properties.
Remove the relay from the housing and shake it near your ear. If you hear a rattling sound similar to the clinking of coins in a jar, then the internal mechanism is damaged and the relay needs to be replaced. Also check the thermal relay (overheat protection), which is often built into the overall housing or located nearby. It should “ring” when dialing, signaling the integrity of the circuit.
For a more accurate test of the relay, you can use a multimeter in dialing mode. The contacts must ring in a certain position, and when turned over (simulating the operation of a gravitational relay), they must open or close, depending on the design. If the relay fails the test, replacing it will cost much less than buying a new compressor.
How does a thermal relay work?
A thermal relay contains a bimetallic plate that bends when heated. If the current in the circuit exceeds the norm or the compressor operates for too long, the plate opens the contacts, de-energizing the engine and preventing its combustion.
Connection diagram and pinout of contacts
To correctly connect or check the compressor, you must clearly understand the pinout of its terminals. The terminal block usually has three pins arranged in a triangle. The location of the contacts may vary depending on the manufacturer: Danfoss, Secop or Chinese analogues. It is important not to confuse the working and starting windings when connecting directly.
You can determine the purpose of the contacts by the winding resistance measured earlier. Between the working and starting windings the resistance will be greatest. The contact that remains free when measuring the highest resistance is common (C). Between the common contact and the working winding (R), the resistance will be less than between the common and the starting winding (S).
- 🔌 Common contact (C): one of the power supply wires is connected to it.
- ⚙️ Working winding (R): has lower resistance, connected via a thermal relay.
- 🚀 Starting winding (S): has a higher resistance, is connected through a starting relay.
When assembling the circuit, it is important to follow the sequence: first a phase is supplied to the common contact, then through a thermal relay the current goes to the working one winding, and the starting winding is energized only at the moment of start. An error in the connection can lead to humming of the motor without rotation of the shaft and rapid overheating.
Direct compressor start technology
Direct starting of the compressor is a method of eliminating the starting relay from the circuit to check the performance of the engine itself. This method allows you to determine whether the motor is able to start when voltage is directly applied to the working and starting windings. To carry out the procedure, you will need a piece of wire with a plug and, possibly, a button or switch to briefly close the starting winding circuit.
Assemble a simple circuit: connect one wire from the plug directly to the common contact of the compressor. Divide the second wire: connect one end to the contact of the working winding, and use the other end to briefly touch the contact of the starting winding. The moment you touch the starting contact, the motor should make a hum and start. After starting, the starting wire can be removed, the engine will operate on the working winding.
If the motor starts and runs smoothly, picking up speed, then the compressor itself is working, and the problem lies in the starting relay or thermostat. If you only hear a hum and the shaft does not rotate, the piston group may be jammed or the oil level is critically low. In some cases, a light blow to the body with a wooden handle at the moment of applying voltage helps, but this is a temporary measure.
⚠️ Attention: Do not keep the starting winding connected for more than 2-3 seconds after starting. Prolonged supply of voltage to the starting winding will lead to its burnout, since it is not intended for constant operation.
There is a nuance with capacitor motors, where the starting winding is not completely turned off, but in household refrigerators, circuits are most often used that turn off the starting winding after gaining speed. Be careful when identifying the type of your unit.
Analysis of the causes of failure and further actions
If after all the checks it turns out that the compressor is electrically operational, but does not start even with direct voltage applied, most likely the problem is mechanical. This may be jamming of the piston group due to exhaustion, lack of lubrication, or solid particles entering the system. In such cases, the motor hums, consumes a lot of current, but the shaft stands still.
Another reason may be the loss of freon. Although this does not affect the electrics of the motor, many modern refrigerators are equipped with sensors that block the compressor from starting if there is no pressure in the system. Check for leaks by oily stains at the joints of the tubes.
- 🛠️ Replacing the relay: if the motor starts directly, replace the starting relay with a similar one.
- 🔄 Replacing the compressor: if the windings are broken or there is a breakdown in the housing, a complete replacement of the unit with evacuation and refueling.
- 🔧 Mechanical repair: trying to wedge the motor often gives a temporary effect and is not recommended.
When deciding on repairs, weigh the cost of a new compressor and the work of a technician. Sometimes it is easier to buy a new refrigerator than to restore an old one, especially if it is more than 10 years old. However, if the problem is only in the relay, the repair will extend the life of the equipment for years.
Is it possible to check the compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without a multimeter. However, you can try to start the motor directly through a working relay from another compressor or using the “poke” method in compliance with safety measures, but this will not provide information about a breakdown to the housing or an interturn short circuit.
Why does the compressor hum, but does not start?
A hum without starting usually indicates that voltage is supplied to the windings, but there is not enough starting torque to rotate the shaft. Reasons: jamming of the mechanics, malfunction of the starting relay (does not supply an impulse to the starting winding) or low voltage in the network.
What resistance should be between the contacts?
The resistance depends on the power of the motor. For household refrigerators, it usually ranges from 10 to 40 ohms. The main rule: the resistance between the working and starting contacts must be equal to the sum of the resistances of each of them relative to the common contact.
Is it dangerous to connect the compressor directly?
Yes, it is dangerous. You work with mains voltage 220V. Additionally, improperly connecting the starting winding can burn out the motor in seconds. The lack of thermal protection with direct connection also creates a risk of overheating and fire.