A modern household refrigerator is a complex electrical system, where the heart is a compressor unit. The ability of equipment to maintain a given temperature regime inside the chambers depends on its serviceability. When the device stops starting, hums but does not pump freon, or knocks out the automatic fuses in the panel, the first thing to suspect is an electrical malfunction of the engine. In such situations, it is critical to know how to ring the compressor windings in order to eliminate the costly replacement of the unit without the need or, conversely, to confirm its failure.
The diagnostic process requires accuracy, basic knowledge in electrical engineering and the appropriate tool. Multimeter is the main device in the arsenal of a home master, allowing you to measure the resistance of the circuit and determine the integrity of the conductors. Incorrect connections or ignoring safety precautions when working with high voltage can lead to serious injury or permanent failure of the equipment. Therefore, before starting any work, it is necessary to completely disconnect the refrigerator from the power supply and provide access to the motor.
In this article we will analyze in detail the algorithm for checking the starting relay, measuring the resistance between the terminals and diagnosing a breakdown of the housing. You will learn what values are considered normal for different types of motors, how to distinguish an open circuit from a short circuit, and what to look for when visually inspecting contacts. Understanding these processes will help you make an informed decision about repairing or replacing the unit.
Preparation for diagnostics and safety precautions
Before you begin directly measuring electrical parameters, it is necessary to ensure safe working conditions. The refrigerator must be unplugged from the outlet at least 10-15 minutes before starting work so that the capacitors discharge and the heated elements cool down. If the appliance is built into a kitchen unit, it should be carefully pulled out, providing free access to the back wall. In some models, such as Indesit or Ariston, access to the compressor may be closed with a decorative cover that needs to be removed.
The main tool for checking is a digital multimeter. Before starting measurements, make sure that the probes of the device are in good condition and the battery is not discharged. Switch the device to resistance measurement mode (Ohms), selecting a limit of 200 Ohms or dialing mode with a sound signal. You will also need a screwdriver to remove the terminal box and, possibly, pliers to carefully remove the contact groups from the start relay.
⚠️ Attention! It is strictly forbidden to measure resistance or continuity measurements of live circuits. This will cause instant failure of the multimeter and can be life-threatening.
It is also important to carry out a visual inspection. If traces of melting, soot or oil are visible on the compressor housing, this may indicate an interturn short circuit or overheating. In such cases, further diagnostics may be impractical, since the unit requires replacement. Inspect the wires going to the terminals: they should be intact, without signs of overheating of the insulation.
Removing the starting relay and access to the contacts
In order to ring the windings, you need to gain access to the contact pins coming out of the compressor housing. These pins usually carry a start relay and a thermal protection relay, either combined into one unit or located separately. This assembly must be removed with extreme caution, as the plastic housings of old relays can be fragile. Usually it is enough to slightly rock the relay from side to side, holding the compressor with your other hand.
After removing the relay, you will see three contacts arranged in a triangle. They may be marked, but most often you have to navigate by their location. On many compressors, for example models Atlant or Beko, the pin layout is stamped on the metal casing or indicated on a sticker nearby. If the markings are erased, you can determine the purpose of the contacts by their size and location: the two upper contacts are usually closer to each other, and the third (common) is located below or to the side.
Before connecting the multimeter probes, it is recommended to clean the contacts from oxides. To do this, you can use fine sandpaper or a blade, carefully scraping off the dark deposits until the metal shines. Oxidation can significantly distort the meter readings, creating a false impression of high resistance or an open circuit. Make sure there are no jumpers or debris between the pins.
⚠️ Attention! When removing the relay, pay attention to the orientation of the contacts. Installing the relay in an inverted position during assembly can lead to a short circuit and burnout of the windings the first time you turn it on.
Determining the purpose of the compressor terminals
The standard single-phase asynchronous motor used in refrigerators has three terminals. Two of them belong to the starting winding, two to the working winding, and one contact is common to both circuits. Understanding this circuit is necessary to correctly interpret multimeter readings. Typically, the conclusions are designated in Latin letters: C (Common) - general, S (Start) - starting, R (Run) - working. In European markings they can be designated as C, L (Line) and R.
To determine which pin is responsible for what, it is necessary to take a series of three resistance measurements between each pair of contacts. The logic here is simple: the greatest resistance will be between the starting and working terminals (S and R), since both windings are connected in series in this circuit. The least resistance will be between the common terminal and the working one (C and R), since the working winding is wound with a thicker wire and has fewer turns. The average value will indicate the circuit between the common and starting terminals (C and S).
Let's look at an example. Suppose we measured the resistance between three contacts and obtained the following values: between 1 and 2 - 25 Ohms, between 2 and 3 - 10 Ohms, between 1 and 3 - 15 Ohms. The sum of 10 and 15 gives 25, which confirms the serviceability of the circuit. In this case, contact 2 is common (since it participates in two smaller resistances), contact 3 is working (lowest resistance with the common), and contact 1 is starting.
Why are the resistances different?
The working winding is wound with a thick wire and occupies 2/3 of the slots of the stator, so its resistance is less. The starting winding has more turns of thinner wire to create a phase shift, so its resistance is higher.
The procedure for measuring resistance and deciphering the readings
The direct dialing process takes several minutes, but requires care. Apply the multimeter probes to a pair of contacts and wait until the readings on the screen stabilize. Digital instruments may display values with an error, so it is important to take into account the resistance of the probes themselves (usually 0.3–0.8 ohms), although this can often be neglected for diagnosing refrigerators. Write down all three obtained values for analysis.
The normal resistance of the working winding is in the range from 10 to 30 Ohms, and the starting winding is from 20 to 60 Ohms, depending on the power of the motor and the model of the refrigerator (for example, for LG or Samsung the values may differ). If the device shows one (infinity) at the 200 Ohm limit, this indicates an open circuit. If the resistance is close to zero (0.1–0.5 Ohm) without a characteristic drop during warming up, a short circuit of the turns is possible, although an accurate diagnosis requires more complex current measurements.
Below is a table with approximate resistance values for various states of the windings:
| Circuit condition | Indications multimeter | Diagnosis | Actions |
|---|---|---|---|
| Good winding | 10–60 Ohm (depending on the pair) | Normal | Continue relay diagnostics |
| Open circuit | 1 (infinity) | Break wire | Replace the compressor |
| Short short circuit | 0.0 – 1.0 Ohm | Short circuit of turns | Replacement of the compressor |
| Breakdown to the housing | There is resistance between the contact and the housing | Short circuit to ground | Urgent replacement |
It is important to note that resistance values may vary slightly depending on engine temperature. On a hot compressor the resistance will be higher than on a cold one. Therefore, if you just tried to start the refrigerator and it overheated, let it cool to room temperature before taking measurements.
Checking for insulation breakdown (short to housing)
One of the most dangerous malfunctions is breakdown of winding insulation on the metal body of the compressor. In this case, when connected to the network, a current leak will occur, which can lead to an electric shock when touching the refrigerator or tripping an RCD in the electrical panel. To check this malfunction, the multimeter is switched to resistance measurement mode at the maximum limit (usually 2000 kOhm or 2 MOhm).
One probe is applied to any of the three contacts of the block, and the second is applied to a cleaned place on the metal body of the compressor (you can use the relay mounting location or cleaned paint next to the terminals). In good condition, the device should show infinity (one in the most significant digit). The appearance of any digital values indicates a violation of the insulation.
⚠️ Attention! If a breakdown is detected in the housing, the operation of such a refrigerator is strictly prohibited. This creates a direct threat to people's lives, especially in conditions of high humidity in the kitchen.
Sometimes the breakdown can be “floating” and appear only when heated or vibration. If the multimeter shows the norm, but knocks out plugs during operation, an accurate diagnosis may require a megohmmeter that supplies high voltage to check the insulation. However, at home, the presence of a resistance of less than 20 MOhm between the winding and the housing is already considered a sign of a malfunction.
Diagnostics of starting and thermal relays
Often the cause of a non-working compressor is not the motor itself, but a faulty starting relay. This device is responsible for briefly supplying voltage to the starting winding at the moment of start. Inside the relay there may be a posistor (thermistor) or an electromagnetic coil with a moving contact. When shaken, a working relay should not make rattling sounds (if it is not collapsible with a posistor), and there should be no burning inside.
The thermal relay protects the motor from overheating. It opens the circuit when the permissible temperature is exceeded. You can check it by dialing: in a cold state the contacts should ring (resistance is close to zero). If the circuit is open when the relay is cold, it is faulty. Also visually inspect the contacts for burning. Black carbon deposits on the contacts increase the contact resistance, causing heating and false protection activations.
☑️ Checking the compressor relay
In some modern models of refrigerators, for example, with inverter compressors Whirlpool or Haier, there may not be a classic starting relay. The engine is controlled by an electronic unit, and the windings there are checked according to a different scheme, often requiring connection to the service port. For such units, a simple test with a multimeter provides only basic information about the absence of a break.
Analysis of results and decision making
After all measurements have been carried out, it is necessary to analyze the data obtained. If the resistance between the terminals is normal and there is no breakdown to the housing, but the compressor does not start (hums and clicks), the problem may lie in a jammed mechanical part or low voltage in the network. In case of jamming (“wedge”), an attempt to start may be accompanied by a strong hum and rapid heating of the housing, after which the thermal protection is activated.
If the measurements show a break or short circuit, the compressor must be replaced. Repairing such motors at home is impossible, since it requires rewinding the stator under special conditions and hermetically sealing the casing. The cost of such repairs is often comparable to the purchase of a new unit or even a whole refrigerator.
When deciding on a replacement, it is important to take into account not only the electrical parameters, but also the overall dimensions, type refrigerant and power of the old compressor. Installing a motor that is not suitable for power will lead to incorrect operation of the refrigerator and rapid failure of the new part. Always check the markings and model when selecting a spare part.
Frequently asked questions (FAQ)
Is it possible to start the compressor directly without a relay?
You can start the engine for a short time by applying voltage to the working and starting terminals at the same time, but doing this is dangerous and is not recommended without experience. The starting winding is not designed for long-term operation and will burn out in a few seconds if the voltage is not removed. In addition, there is a risk of electric shock.
Why does the multimeter show a different resistance when taking repeated measurements?
This may be due to a change in the temperature of the windings (metal resistance depends on temperature) or the presence of oxides on the contacts, which are penetrated by the current of the device at the first touch. Discharge of the residual magnetic field or capacitance is also possible if measurements were taken immediately after operation.
What to do if the resistance of the starting and operating windings is the same?
In some types of engines (rarely for refrigerators, more often for other equipment) the windings may be identical. However, this is not typical for refrigeration compressors and may indicate an interturn short circuit in one of the windings, which has changed its parameters. A comparison with the passport data of a specific model is required.
Can there be a break inside the compressor if the wires are intact outside?
Yes, a break can occur inside the sealed casing, for example, at the point where the lead is soldered to the winding or due to a wire burnout inside the stator. In this case, the multimeter will show infinite resistance, and the compressor will have to be changed, since opening the casing at home is impossible.
Inverter compressors
Modern refrigerators often have inverter motors. They cannot be checked by simply connecting to 220V. Testing the windings with a multimeter is possible (three pairs of contacts with approximately the same resistance should ring), but starting is possible only through a special control unit.