Diagnostics of the compressor: how to check the motor on the refrigerator with a multimeter

The situation when the refrigerator suddenly stops cooling, and the ice inside has already begun to melt, always causes panic. First of all, we check whether the light is on and listen to the operation of the unit. If the light is on, but there is no characteristic hum of the motor, or it turns on for a couple of seconds and immediately clicks when it turns off, then with a high degree of probability the problem lies in the electrical part of the compressor.

Before calling a technician or taking the equipment to a service center, it is worth carrying out the initial diagnostics yourself. To do this, you only need multimeter (tester) and a minimum set of tools. Correctly checking the motor windings can save you a significant amount if you yourself identify an open or short circuit, or, conversely, realize that the problem is in cheaper parts, such as the starting relay.

In this article we will analyze a step-by-step algorithm of actions that will allow you to determine the condition electric motor without complicated laboratory conditions. You will learn what resistance values are considered normal, how to distinguish a working unit from a burnt one and what to look for when visually inspecting the contacts.

Safety precautions and preparation for diagnostics

Working with electrical appliances requires strict adherence to safety rules, since the refrigerator operates from a 220 network volts, which is life-threatening. Before starting any manipulations, be sure to disconnect the unit from the power supply by removing the plug from the socket. Do not rely solely on the thermostat - physically disconnecting the cord is the only guaranteed way to protect yourself from electric shock.

To conduct a quality diagnosis, you will need to prepare a workplace and tools. You will need to access the back of the refrigerator where the compressor is located. Dust and dirt often accumulate there, so pre-cleaning won't hurt. Also prepare the following tools:

• 🔧 Multimeter (analog or digital) with the function of measuring resistance (Ohm).
• 🔧 Set of screwdrivers (flat and Phillips) for removing the protective casing.
• 🔧 Pliers or pliers for careful removal terminals.
• 🔧 Insulating tape or casings for marking wires.

⚠️ Attention: It is strictly forbidden to touch the metal parts of the compressor or electrical contacts with wet hands. The capacitor in the circuit may retain a residual charge, so be careful when touching the relay contacts.

Make sure there is enough space and lighting around the compressor. If the refrigerator is built-in, it may have to be moved away from the wall. Remember that the compressor is a sealed unit, and you cannot open its housing, but access to the electrical terminals is usually open after removing the plastic cover.

Removing the protective casing and accessing the contacts

To ring the engine, you need to get to the contact group. On the back wall of the refrigerator, in its lower part, there is a black barrel-shaped element - this is compressor. A plastic or metal box is attached to the side or bottom of it, which protects the start relay and contacts from dust and moisture.

The process of removing the casing is usually not difficult. Fastening elements may differ depending on the refrigerator model Indesit, Beko or LG. In some cases the cover is held in place by latches, in others by screws. Carefully unscrew the fasteners or open the latches, being careful not to damage the plastic elements that could become fragile over time.

After removing the cover, you will see the start relay, which is placed on three contact pins coming out of the compressor housing. It is these contacts that we will need to check. Before removing the relay, it is strongly recommended to photograph the location of the wires or mark them with a marker so as not to confuse the polarity during assembly.

Carefully remove the start relay from the contacts. It can be removed with a little force, but be careful not to break the plastic mounting tabs. Below the relay you will see three terminals forming a triangle. These are the winding inputs of the electric motor.

Connection diagram and pin markings

Before picking up a multimeter, it is important to understand what exactly we will measure. The refrigerator compressor is a single-phase asynchronous motor that has two main operating windings and one starting winding. On the terminal block, the terminals are usually marked with letters or symbols, but over time the markings can be erased or covered with paint.

The standard terminal marking on most modern compressors is as follows: the letter C (Common) indicates a common point, R (Run) - the working winding, and S (Start) - launcher. In some models of European manufacturers, such as Electrolux or Zanussi, numbers or color designations may be used instead of letters.

Deciphering rare markings

On some old Soviet-made models or specific series, markings may be missing. In this case, the resistance between the terminals will help determine their purpose: the greatest resistance will be between the starting and working windings, and the smallest - between the working and common points.

For ease of memorization and correct diagnosis, check the table below, which shows typical resistance values for a working motor:

It is important to understand that the exact numbers may vary depending on the power of the motor and manufacturer. For example, powerful inverter models may have lower resistances. The main thing here is not a specific number, but the ratio of values ​​and the absence of a short circuit.

Checking the windings for open circuits and short circuits

Now we move on to the most important stage - measuring resistance. Switch the multimeter to resistance (ohms) measurement mode, selecting a limit of 200 ohms or 2 kohms. If you have an analog device, do not forget to calibrate the pointer to zero before starting measurements.

First of all, you need to exclude a breakdown on the housing. Touch one multimeter probe to any of the three contacts on the compressor, and the other to a cleaned area on the metal case (where there is no paint or rust). If the device shows infinity (one in the most significant digit or the needle does not deviate), then the insulation is intact. If the multimeter shows any resistance value, even a large one, this indicates insulation breakdown.

⚠️ Attention: The presence of resistance between the winding and the body means that the refrigerator can “shock” current when touched, and the circuit breaker in the panel will knock out when turned on. Operation of such a unit is prohibited.

Next, we check the integrity of the windings themselves. Measure the resistance between each pair of contacts:

• 🔍 Between terminals R and C (working winding).
• 🔍 Between terminals S and C (start winding).
• 🔍 Between terminals S and R (total resistance).

The test logic is simple: resistance between S and R must be equal to the sum of the resistances S-C and R-C. If the multimeter shows zero in all cases, there is a short circuit in the turns. If the device shows infinity in at least one pair (except for the housing), it means there is a break in the winding break.

Diagnostics of the starting relay and thermocouple

It often happens that the engine itself is working fine, all the windings are ringing, but the refrigerator does not start. In this case, the problem lies in the start relay or protective thermocouple. The starting relay is responsible for briefly supplying voltage to the starting winding at the time of start.

Visually inspect the relay. If the ringing of a gold-plated ball is heard inside (in a relay with a posistor) or traces of burning, soot and plastic melting are visible, the part requires replacement. You can check the integrity of the thermocouple (protective element) with a multimeter in continuity mode. The resistance of a working thermocouple should be close to zero.

To check the relay mechanism itself, you need to carefully open it (if the design allows) or apply voltage to the coil separately, observing safety precautions. However, it is easier and more reliable to replace a suspicious relay with a new one, since the cost of this part is low, and its failure simulates a breakdown of an expensive compressor.

Please note that in modern refrigerator models Samsung or LG Electronic control boards can be used, which also control the launch. If everything is in order with the relay and motor, the start signal may not be coming from the control module.

Interpretation of results and common errors

After all measurements have been taken, it is necessary to correctly interpret the data obtained. Many beginners make the mistake of considering any multimeter reading other than zero or infinity to be normal. However, an interturn short circuit is an insidious fault that is difficult to detect with a conventional tester.

If the winding resistance is significantly lower than the rated values ​​(for example, 2-3 Ohms instead of 20), this may indicate a partial short circuit of the turns. Such an engine can hum, overheat and eventually burn out. It is also worth paying attention to the color of the oil if it is possible to check it through the service valve (although this is already a level of advanced repair).

⚠️ Attention: Technical characteristics of compressors may vary depending on the specific model and year of manufacture. Always check the manufacturer's official documentation or technical bulletins for your series of refrigerators.

A common mistake is to ignore the state of the contacts. Even if the windings are intact, oxidized terminals create high contact resistance, heating and sparking. Sand the contacts with fine sandpaper before installing the relay.

Final operating recommendations

Successfully diagnosing a refrigerator engine is an important skill that allows you to weed out hopeless cases from repairable ones. If your compressor passes the multimeter test but does not work, the problem is most likely in the control system or refrigerant, which requires the attention of a specialist with a gauge manifold.

Regularly clean the condenser (black grill on the back) of dust to ensure proper cooling of the compressor. Overheating is the main enemy of winding insulation, leading to breakdowns. Make sure that the refrigerator stands level and has a gap from the wall for ventilation.

If you find that the motor is faulty (an interturn short circuit or a breakdown to the housing), repair by rewinding at home is impossible due to the need for evacuation and refilling with freon. In this case, a complete replacement of the compressor with one similar in power and refrigerant is required.

Is it possible to start a refrigerator without a relay?

Theoretically, you can start the compressor by applying voltage directly to the starting winding through the capacitor, but this is a temporary measure for testing. Long-term operation without a standard relay will lead to burnout of the windings due to the impossibility of turning them off after the rotor accelerates.

Remember that electricity does not forgive mistakes. If you are not sure of your actions or the readings from the device are contradictory, it is better to stop and contact a professional technician. Take care of yourself and your equipment.

Why does the compressor hum but does not start?

Most often this indicates a jammed mechanical part of the compressor (piston group) or a faulty start relay. If the windings are intact, try gently tapping the compressor housing with a wooden hammer handle in the area of the fastenings, sometimes this helps to remove the jammed shaft.

What multimeter values indicate 100% failure?

An absolute sign of a malfunction is a resistance equal to zero (short circuit) or infinity (break) between the contacts of the windings, as well as the presence of any conductivity between the contacts and the metal body of the unit.

Is it possible to check the compressor without a multimeter?

It is impossible to carry out an accurate diagnosis without instruments. However, an indirect sign of the serviceability of the electrical part is the engine starting when voltage is applied (through a working relay). If, when turned on, the machine in the panel knocks out, there is a short circuit.