An unexpected stoppage of the refrigerator often takes you by surprise, causing panic about the safety of food and the cost of upcoming repairs. In most cases, the cause of the breakdown is a failure compressor, which is the heart of the entire cooling system. Before calling a technician or buying new equipment, it makes sense to conduct an initial diagnosis in order to understand the scale of the problem and eliminate simple malfunctions.
Checking the motor using multimeter is an affordable and effective way to determine the condition of the electrical part of the unit. To carry out the procedure, you do not need complex specialized equipment, just a basic set of tools and compliance with electrical safety rules. Competent diagnostics will allow you to accurately say whether the engine can be restored or requires a complete replacement.
In this article we will analyze in detail the algorithm of actions that will help you identify a break or interturn short circuit. You will learn to correctly interpret instrument readings and understand when repairs are not economically feasible. The accuracy of measurements directly depends on preparation and attentiveness, so special attention should be paid to each stage.
Preparation for diagnostics and safety precautions
The first and most critical stage is the complete de-energization of refrigeration equipment. Never handle any electrical components while the power cord is plugged into an outlet. Even briefly touching live contacts can cause serious shock, so safety should be priority number one.
After unplugging the refrigerator, you need to gain access to the compressor, which is usually located in the lower back of the cabinet. You will need to remove the protective panel or cover that covers the motor. Often there is also a start-protection relay, which will also need to be carefully disconnected from the motor contact group.
⚠️ Attention: Before starting work, make sure that the capacitors in the circuit (if your relay model has them) are completely discharged to avoid residual discharge.
To carry out high-quality diagnostics, prepare the following tool kit:
- 🔌 Digital multimeter with continuity and resistance measurement function.
- 🔧 Set of screwdrivers for removing panels and terminals.
- 🧤 Dielectric gloves for additional hand protection.
- 🔦 Flashlight for better illumination of the work area in niche.
Visually inspect the compressor itself and the tubes suitable for it. If you notice traces of oil, soot, or melted wire insulation, this may indicate overheating or mechanical damage. In such cases, the likelihood of successful repair of the electrical part is significantly reduced, and often replacement of the entire unit is required.
Removing the start relay and accessing the contacts
To ring the windings, you need to release the three contacts located at the end of the compressor. They are closed with a plastic case starting relay and a protective box. Carefully press out the retaining clips or unscrew the mounting screws to remove the cover. Do not use excessive force, as plastic becomes brittle over time.
The relay is usually simply put on the contacts and is held in place due to the tightness of the fit and its own weight. Remove it by pulling it down or to the side, depending on the design. On the inside of the cover you will see a connection diagram, which may be useful during assembly, but for diagnostics it is important for us to have access to the engine legs themselves.
The contacts may be oxidized or coated with carbon deposits, which distorts the readings. Before measurements, it is recommended to carefully clean the terminals with fine sandpaper or alcohol. This will ensure reliable contact of the tester probes and will allow you to obtain reliable data on the condition of the windings.
Checking the resistance of the windings with a multimeter
The main task at this stage is to measure the resistance between the three contacts of the compressor. They are usually designated by the letters C (Common), S (Start) and R (Run), but older models may not have the markings. You need to ring all the pins in pairs by switching the multimeter to the resistance measurement mode (Ohm).
Attach the probes to different pairs of contacts and write down the values obtained. A resistance in the range from 10 to 60 ohms is considered normal. If the device shows one or infinity, this indicates a break circuit. If the resistance is close to zero, an interturn short circuit has probably occurred.
The table below shows approximate resistance values for a working compressor of different types:
| Pair of contacts | Normal resistance | Possible malfunction |
|---|---|---|
| Starting - Working | Sum of the other two | Normal |
| Working - General | 10-30 Ohm | Open or short circuit |
| Starting - Common | 20-40 Ohm | Open or short circuit |
| Any pair | 0 Ohm | Short Circuit |
It is important to understand that values may vary depending on engine power and manufacturer. The main rule: the resistance between the starting and working windings must be equal to the sum of the resistances of each of them relative to the common contact. A violation of this mathematical relationship indicates a hidden defect.
What to do if the readings float?
If the numbers on the multimeter screen are constantly changing, this may indicate poor contact of the probes or the presence of moisture inside the windings. Try warming up the compressor with a hairdryer (without overheating!) and repeat the measurement.
Diagnostics of breakdown to the housing (Short to ground)
One of the most dangerous malfunctions is an insulation breakdown when voltage reaches the metal housing of the compressor. This not only disables the equipment, but also creates a real threat to the lives of users. You can check for breakdown by measuring the resistance between any contact and a copper tube or unpainted part of the case.
Switch the multimeter to the resistance measurement mode at the maximum limit or to the continuity mode. Press one probe to any of the three contacts, and the second to the place on the body or tube that has been cleared of paint. If the device shows a resistance of less than 2-5 MOhm or emits a sound signal, it means that the insulation is broken.
⚠️ Attention: Operating a refrigerator with a breakdown in the body is strictly prohibited, as this can lead to an electric shock when touching the metal parts of the unit.
The cause of the breakdown is often the aging of the insulation due to overheating or mechanical damage to the windings. Unfortunately, it is impossible to restore the insulation inside a sealed casing at home. In such a situation, a complete replacement of the compressor is required, since further operation is unsafe.
Analysis of the starting relay and protective thermostat
Often the compressor itself turns out to be working, and the problem lies in the attached equipment. Start relay is responsible for the short-term supply of voltage to the starting winding, and a thermal relay protects the motor from overloads. If these elements are faulty, the motor simply will not start, although electrically it may be intact.
Check the relay for visible traces of burning or melting. Ring his contacts in different positions. For electromagnetic relays, the coil resistance must be within normal limits, and the contacts must open when in a vertical position (shaking). The thermal relay in a cold state should ring short.
- 🔍 Visually inspect the contacts for carbon deposits.
- ⚡ Ring the relay coil circuit (there should be resistance).
- 🌡 Check the thermal release (should ring at cold).
- 🔄 Shake the relay - there should be no knocking of the ball inside.
If the relay is stuck in the “on” position, this can lead to burnout of the starting winding. If it does not close, the engine will hum, but will not start. Replacing these components is inexpensive and often solves the problem of a “non-working compressor.”
☑️ Relay diagnostics
Interpretation of results and decision-making
After receiving all the data, it is necessary to make a final conclusion about the condition of the refrigerator. If measurements show a break or short circuit in the windings, as well as a breakdown in the housing, the compressor is considered faulty. Repair in this case consists only of replacing the unit, since rewinding the motor in a hermetically sealed design is not economically feasible.
If the electrical part is normal (the resistance is fine, there is no breakdown), but the refrigerator does not work, the problem may be mechanical. Jamming of the piston group or lack of freon cannot be diagnosed with a multimeter. In such a situation, the participation of a specialist with a pressure gauge manifold and a vacuum pump will be required.
If you find a faulty relay, replacing it can bring the refrigerator back to life at minimal cost. However, if the motor itself burns out, estimate the cost of a new compressor and the work to replace it. For older models of refrigerators, it is sometimes more profitable to purchase new equipment than to repair old equipment.
⚠️ Attention: Technical characteristics of compressors may vary depending on the model. Always check the parameters with the data on the nameplate of a specific device before purchasing spare parts.
Frequently asked questions (FAQ)
Is it possible to start the compressor directly without a relay?
Technically, you can start the engine by applying voltage directly to the working and starting windings, but doing this is dangerous and is not recommended without experience. This may cause the windings to burn out quickly or cause personal injury. This method is used by craftsmen only for a short-term check of the motor's performance.
What resistance is considered normal for different brands?
In most household refrigerators (Indesit, LG, Bosch, Atlant), the resistance of the working winding is 10-25 Ohms, and the starting winding is 20-45 Ohms. The exact values depend on the motor power indicated on the label, but the principle of the “sum of resistances” remains universal.
Why does the compressor hum, but does not start?
The hum indicates that current is supplied to the motor, but the rotor cannot turn. Reasons: jamming of the mechanical part, a malfunction of the starting relay (does not give an impulse to start) or an interturn short circuit that creates insufficient force to start.
Is it possible to check the compressor without a multimeter?
It is impossible to carry out accurate diagnostics without measuring instruments. You can only indirectly judge the problem: if the machine knocks out when you turn it on or you hear a clicking and buzzing sound, an electrical or mechanical malfunction is likely. However, the diagnosis can only be confirmed with a tester.