The situation when the refrigerator stops cooling and the start relay makes a characteristic click or crackles is familiar to many. At such moments, there is an urgent need to check the performance of the compressor itself, eliminating the automatic starting system from the chain. Direct testing electric motor allows you to accurately determine whether the “heart” of the refrigeration system is alive, or whether the problem lies in burnt-out windings, an internal break or an interturn short circuit. Without this stage, further repairs make no sense, since replacing the relay on a faulty motor will not produce results.
The diagnostic procedure requires care and compliance with safety regulations, because you will be working with high voltage. However, with basic knowledge of electrical engineering and a multimeter, any home mechanic can carry out initial diagnostics. We will consider methods that do not require complex equipment, but give an unambiguous answer about the state of electrical part the unit. It is important to understand that even if the motor starts, this does not guarantee its full serviceability in the operating cycle, but it will cut off obviously dead options.
In this article we will analyze in detail the algorithm of actions, methods of connecting directly and methods for measuring winding resistance. You will learn how to distinguish the starting winding from the working winding, what values are considered normal for different types of compressors, and what to do if the device readings are strange. A competent check starting device of the engine itself will save time and money, allowing you to immediately make a decision on purchasing a new unit or replacing the unit.
Safety measures and preparation for diagnostics
Before you begin manipulating electrical equipment, it is necessary to ensure complete security. The first and most important step is to physically disconnect the refrigerator from the electrical network. It is not enough to simply turn off the device with the button, if there is one - you need to unplug the cord from sockets. Any work under voltage is strictly prohibited, since the risk of electric shock in this case is extremely high.
After turning off the power, give the capacitors and internal circuits time to discharge, although in household models this happens quickly. You will need access to the lower rear of the refrigerator where the compressor compartment is located. Remove the protective cover, which is usually secured with latches or screws. You will see a black barrel-shaped unit, to which a refrigerant pipe and electrical wires fit.
⚠️ Attention: Never cut through or damage the copper pipes of the cooling system. If freon comes out of them under pressure, it can be dangerous, and restoring the tightness will require expensive equipment and a technician.
To carry out high-quality diagnostics, you will need certain tools. Without them, verification will be incomplete or impossible. Prepare the following set:
- 🔧 Multimeter (tester) with the ability to test and measure resistance.
- 🔧 Screwdrivers (phillips and flat) for removing terminals and covers.
- 🔧 Pliers for carefully removing connectors.
- 🔧 Insulating tape or heat shrink to temporarily insulate contacts.
Make sure the work area is well lit and the floor is dry. Wet surfaces or puddles of water near exposed wiring are not permitted. If the compressor is hot after recent operation, allow it to cool to avoid burns and for resistance readings to be more accurate, as temperature coefficient affects the resistance of metals.
Visual inspection and removal of the start relay
The first stage of verification is a careful visual inspection. Often external signs can point to a problem faster than measurements. Inspect the compressor housing for swelling, oil leaks or burnt marks. The presence of oil in the lower part of the compressor compartment may indicate depressurization of the system, which makes further electrical checks pointless - such a unit requires replacement or complex repairs with refilling.
Pay special attention to the starting relay. This is a small box placed on the side or bottom fitting of the compressor, which contains three contacts. Carefully remove the relay. It is usually held in place by latches or a bracket. If the relay is cracked, melted, or emits an unpleasant burning odor upon visual inspection, there is a good chance that it has failed due to overload or old age. However, our goal is to check the electric motor itself.
Having removed the relay, you will see three leads protruding from the compressor housing, arranged in a triangle. These are the inputs to the motor windings. They may be coated with oxide or dirt. Wipe them gently with a dry cloth. If the contacts are heavily oxidized, they can be cleaned with fine sandpaper, but be careful not to break off the leads, as they are fragile and soldered into the housing.
Check the integrity of the wires going to the relay. If the insulation is melted or the wires rub against the housing, this could cause a malfunction. Before connecting directly, make sure that the wires with which you will supply voltage are in good condition and have a sufficient cross-section to withstand the starting current of the compressor.
Testing the windings with a multimeter
The most reliable method of primary diagnosis is measuring the resistance of the windings. This method allows you to detect an open circuit or short circuit. Switch the multimeter to resistance (Ohm) measurement mode, selecting a limit of 2 kOhm or 200 Ohm. First check for a short to body. Touch one probe to any of the three terminals of the compressor, and the other to a cleaned place on the metal case (where there is no paint or rust).
If the device shows a resistance close to zero or emits a beep, it means something has happened insulation breakdown to the case. Such an engine cannot be operated - it is mortally dangerous. If the device shows infinity (one in the most significant digit or OL), then the insulation is intact, and you can proceed to measuring the resistance between the terminals themselves.
You have three contacts. Let's call them 1, 2 and 3. You need to make three measurements: between 1 and 2, between 2 and 3, and between 1 and 3. Write down the values obtained. Typically the circuit looks like this: the highest resistance is between the starting and working windings (total), the average is on the working winding, the smallest is on the starting winding. However, the exact values depend on the model.
Let's consider typical values for popular types of compressors. The data may vary, but the order of the numbers is usually preserved.
| Measurement type | Normal value (Ohm) | What does it mean |
|---|---|---|
| Working winding | 10 - 25 Ohm | Main winding, thick wire |
| Start winding | 20 - 45 Ohm | Winding with high resistance, thin wire |
| Total (between extreme) | 30 - 70 Ohm | Sum of resistance of both windings |
| To the body | Infinity | No insulation breakdown |
If you receive values that are very different from the norm (for example, 1-2 Ohms or a complete lack of response from the device), this indicates a malfunction. Interturn short circuit often manifested by low resistance, and a break - a complete absence of readings. In such cases, the engine must be replaced.
Scheme of direct connection to a 220V network
If the continuity test showed normal resistance values, you can try to start the engine directly, bypassing the relay. This is the most risky stage, requiring maximum concentration. The essence of the method is to apply voltage to the working winding and a short-term pulse to the starting winding. To do this, you will need a piece of wire with a plug and, preferably, a button to break the circuit or a trigger.
Determine which contacts correspond to the working and starting windings. As a rule, the resistance between the working and common contacts is less than between the starting and common contacts. The common contact (Common) is often located separately from the pair or marked with a letter C. The working winding (R or Run) has a lower resistance, the starting winding (S or Start) has a higher resistance.
The connection diagram is simple: one wire from the network (phase) is connected to general contact. The second wire (zero) goes to the working winding. To start, you need to briefly apply voltage to the starting winding. In a factory relay, this function is performed by a capacitor or mechanical breaker. In manual mode, you can use the button or just briefly touch the contact with the wire, but be prepared for sparks.
☑️ Direct start algorithm
When power is applied, the engine should emit a smooth hum. If a hum is heard, but the shaft does not rotate, and after 2-3 seconds the machine knocks out or a loud crack is heard, it means the motor is jammed. Do not keep the power on for a long time, so as not to completely burn the windings. If the motor starts, it will work until you disconnect it from the network, since the thermal splitter and time relay are excluded from the circuit.
⚠️ Attention: When connected directly, the compressor operates without overheating protection. Keep your hand on the case: if it starts to get hot quickly and strongly, turn off the power immediately. Long-term operation without a relay and freon (if the system is empty) will lead to rapid failure.
Analysis of results and troubleshooting
After the tests, it is necessary to analyze the data obtained. If the engine starts and runs smoothly, does not overheat and creates a vacuum at the inlet (check with your finger, it should be suction), then the electrical part is working. The problem most likely lay in the start relay, which needs to be replaced. However, if the launch was successful, but there are nuances, it’s worth digging deeper.
A common problem is jamming the piston group. The motor hums, the current consumption is high, but there is no rotation. In some cases, “wedging” with a blow or applying increased voltage helps, but it is not recommended to do this at home. If the motor starts only with a kick (turn the shaft by hand, which is difficult due to the design) or works jerkily, its resource is exhausted.
Another important parameter is the current strength. Ideally, you should use current clamps. If the current consumption significantly exceeds the rated one (indicated on the nameplate), it means that there is an interturn short circuit in the windings, even if the resistance rings normally. Such a compressor will not last long and will overheat.
What is a thermal splitter?
This is a protection device built into the relay or on the compressor housing. It opens the circuit when overheated. If it is faulty (always open), the motor will not start. If it is “stuck” (always closed), the motor may burn out if it overheats.
It is also worth checking the condition of the refrigerant. If, when the compressor is operating, air under pressure does not blow from the outlet tube, and there is no suction at the inlet, there may be a freon leak or a clogged capillary system. In this case, an electrically serviceable motor is powerless - you need to call a technician to look for leaks and refuel.
Typical errors when checking a compressor
When diagnosing themselves, beginners often make mistakes that can lead to false conclusions or equipment breakdown. One of the most common is confusion in contacts. Connecting power to the starting winding as a working winding (constantly) will lead to its burnout in a matter of seconds, since it is not designed for long-term operation.
Another mistake is ignoring the wiring condition. An attempt to run a powerful motor through thin wires or strands with poor contact will lead to heating and melting of the insulation at the connection point. Always use wires with a cross-section of at least 1.5 mm² and securely fix the contacts.
Don't forget about the capacitor either. Some circuits (CSR) use a run capacitor that must remain in the circuit at all times. If you exclude it, the engine may not develop the required power or overheat. Carefully study the diagram pasted on the relay body or in the instructions for the model Indesit, Atlant or Beko.
And, finally, the most serious mistake is checking the engine in a closed circuit without the possibility of gases escaping. If you connect a compressor, make sure that the pipes are open. Starting in a closed volume will create excess pressure, which can rip off the cover or damage the valves.
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 a device. However, you can try the “poke” method with caution: apply 220V to the working winding. If it hums and gets hot, the winding is intact. If there is silence, there is a break. But this method will not show a breakdown to the housing or an interturn short circuit, so the use of a tester is preferable.
Why does the compressor hum but does not start?
There may be several reasons: jamming of the piston group (mechanical failure), faulty starting relay (does not give an impulse to start), low voltage in the network or breakage of the starting windings Also often the cause is a starting capacitor that has lost capacity.
What current consumption is considered normal for a household refrigerator?
For most medium-sized household refrigerators, the normal operating current is from 0.5 to 1.5 Amperes. The starting current may briefly jump to 10-15 Amperes. If the operating current exceeds 2 Amperes, this is a sign of a malfunction or problems with the cooling system.
Is it possible to replace a compressor from a refrigerator with another?
Yes, but it is advisable to select an analogue of the same power and cooling capacity. It is also important to consider the type of refrigerant (Freon 134, 600a, etc.) and the type of oil. Installing a more powerful motor can lead to incorrect operation of the system, and a weaker one can lead to its overload.