A sudden stop of the refrigerator often takes you by surprise, especially when there is food in the chamber. One of the most serious and difficult causes to eliminate is malfunction motor-compressor. It is this unit that is responsible for circulating the refrigerant, creating the necessary pressure in the system. If the engine stops starting, hums without result, or knocks out the circuit breakers in the electrical panel, there is a high probability of electrical breakdown or motor-compressor interturn short circuit. Before calling a technician or buying a new unit, it is necessary to carry out initial diagnostics. Testing a compressor for a short is a procedure that requires caution, but can be done by someone with basic electrical skills. Understanding the nature of electrical faults will help you accurately determine whether turn-to-turn short circuit.
Before calling a technician or buying a new unit, it is necessary to carry out initial diagnostics. Testing a compressor for a short is a procedure that requires caution, but can be done by someone with basic electrical skills. Understanding the nature of electrical faults will help you accurately determine whether unit is repairable or requires complete replacement. In this article we will analyze all stages of testing, starting from safety measures and ending with deciphering the multimeter readings.
It is worth noting that modern models, such as Indesit or Atlant, may have a similar design of the starting group, but the location of the pins and parameters windings should always be checked with technical documentation. Ignoring the symptoms can lead to a fire hazard or failure of other expensive components of the control system.
⚠️ Attention: All compressor diagnostic work must be carried out exclusively with the power supply disconnected. Residual voltage in capacitors can be life-threatening.
Symptoms and signs of engine failure
The first step in diagnosis is careful observation of the behavior of the refrigeration equipment. Electrical short circuit rarely occurs asymptomatically. Most often, the owner notices that the refrigerator has stopped freezing, and the compressor itself is either silent or emits a short beep, after which the relay clicks. This is a classic sign that the starting winding cannot start the rotor, or thermal protection is triggered due to increased current.
Sometimes the problem lies deeper, in the violation of the insulation of the wires inside the stator. In this case, when you touch the metal body of the refrigerator, you can feel a slight tingling sensation, and the differential circuit breaker (RCD) in the panel will regularly turn off. This is a direct signal about breakdown on the housing. It is also worth paying attention to the smell of burning or melted plastic in the motor area, which indicates overheating of the windings due to a short circuit of the turns.
It is important not to confuse electrical faults with mechanical jams. If the rotor is jammed, the current in the windings will also increase sharply, but the nature of the damage will be different. For accurate diagnostics, it is necessary to remove the start-up protection relay and gain access to the contact group of the electric motor.
Required tools and safety measures
For a quality check, you will need a minimum set of tools that any home craftsman can find. The main device will be multimeter (tester), capable of measuring resistance in Ohms and checking the integrity of the circuit. It is desirable that the device has an audio test function, as this speeds up the process of searching for breaks and short circuits.
In addition to the measuring device, you will need:
- 🔧 A set of screwdrivers (phillips and flat) for removing casings and relay.
- 🔨 Pliers or side cutters for working with wires and clamps.
- 🧤 Dielectric gloves for protection against accidental electric shock.
- 🔦 Flashlight for illuminating hard-to-reach places in the compressor niche.
Before starting work, make sure that the power cord is unplugged from the outlet. If the refrigerator has just been running, let it cool down to avoid getting burned by the hot pipes or itself. It is also recommended to check the insulation integrity of the wires going to the compressor, as damaged wiring may give false readings during testing. motor housing. It is also recommended to check the integrity of the insulation of the wires going to the compressor, as damaged wiring may give false readings during testing.
Removing the starting relay and accessing the contacts
To check the windings, you need to get to the three terminals located at the end of the compressor. They are covered with a plastic or metal casing, which is part of the start-up relay. The removal process may vary depending on the model. For example, in equipment Liebherr or Bosch the fastenings can be hidden under additional plugs, while in older models ZIL or Turk the relay is simply put on the contacts.
Carefully remove the casing. It is usually held in place by spring clips or latches. Do not use excessive force to avoid breaking the fragile plastic, especially if the refrigerator is old and the plastic has lost its elasticity. Once removed, you will see three contacts arranged in a triangle. There is usually a marking on the compressor itself or on the relay circuit, but it can be erased.
Here is the standard contact diagram for most models:
| Designation | Purpose | Characteristic resistance |
|---|---|---|
| C (Common) | Common contact | Sum of winding resistance |
| S (Start) | Starting winding | High resistance |
| R (Run) | Working winding | Low resistance |
It is important to remember the location of the contacts or photograph them before disconnecting the wires if you plan to install a new starter. Mixing up the phasing when connecting can lead to instant burning out of the new relay or the motor itself.
☑️ Preparation for measurements
Check for insulation breakdown (Short circuit to housing)
The most dangerous type malfunctions are when phase it breaks through the metal housing of the compressor. This poses a direct threat to human life. To check, switch the multimeter to resistance measurement mode at the maximum limit (usually 2 MΩ or 20 MΩ) or to continuity mode.
Press one probe to any of the three contacts on the compressor, and the second to a place on the metal body of the motor that has been cleared of paint (you can use a threaded hole for fastening relay). If the device shows "0" or makes a squeaking sound, it means that the insulation is broken and there is ground breakdown. In this case, operation of the refrigerator is strictly prohibited.
⚠️ Attention: The presence of even a small resistance (less than 10 kOhm) between the contacts and the housing indicates a critical deterioration of the insulation. Such a motor can work for some time, but the risk of electric shock remains high.
Sometimes a breakdown appears only when heated. If the device shows infinity when “cold”, but knocks out the RCD during operation, the problem may lie in the thermal expansion of the windings. In such cases replacing the compressor is the only safe solution, since rewinding the stator in domestic conditions is impossible and economically inexpedient.
Diagnostics of windings for interturn short circuit
An interturn short circuit is a more insidious defect. With it, the insulation between the turns of copper wire inside the stator is broken, which leads to a change winding resistance. The current in the circuit increases sharply, the motor overheats and goes into protection. For diagnostics, it is necessary to measure the resistance between the contacts.
Find the common contact (C). Measure the resistance between C and R (run winding) and between C and S (start winding). The resistance of the working winding is always less than the starting winding. For example, R could be 15 ohms and S could be 30 ohms. If you see values close to zero, it means that a short circuit of the turns has occurred.
Signs of an interturn short circuit:
- 📉 The resistance of the windings is significantly lower than the rated values.
- 🔥 The compressor heats up quickly and strongly (within 1-2 minutes of operation).
- ⚡ The current consumption exceeds the rated current indicated on the tag.
Why does the compressor heat up when shorted?
During a short circuit, parts of the turns are excluded from operation, the total resistance drops. According to Ohm's law, at a constant network voltage, a drop in resistance leads to a sharp increase in current. The increased current causes overheating of the copper and melting of the insulation, which completely disables the motor.
If the resistance between contacts R and S shows infinity, this indicates an open circuit, which also requires replacement of the unit. It is important to understand that a working engine must have stable readings that do not “float” during the measurement process.
Comparative table of normal readings
For ease of diagnosis, we will give approximate resistance values for compressors of different powers. Remember that the exact data depends on the specific model and manufacturer, for example LG and Whirlpool motors with different parameters can be used.
| Power (hp) | Resistance R (Operating), Ohm | Resistance S (Starting), Ohm | Total (R+S), Ohm |
|---|---|---|---|
| 1/8 (small) | 12 - 18 | 25 - 35 | 35 - 50 |
| 1/6 (medium) | 15 - 22 | 30 - 45 | 45 - 65 |
| 1/4 (powerful) | 10 - 15 | 20 - 30 | 30 - 45 |
| Inverter | Nonlinear | Nonlinear | Requires special. test |
If your measurements differ radically from the table ones (for example, they show 0 Ohm or infinity), the motor is faulty. It is also worth checking the resistance between any pair of contacts and the case - it should be infinite.
Frequently asked questions (FAQ)
You can Is it possible to run the compressor bypassing the relay for testing?
Theoretically, it is possible to apply voltage directly to the working winding, but doing this is extremely dangerous without special skills. You can completely kill the engine or get an electric shock. For a one-time check, it is better to use a working starting relay of the same series.
Why does the multimeter show zero and the motor hums?
If the device shows zero between the contacts, this means a short circuit inside the windings. The humming occurs because a magnetic field is created, but the rotor cannot turn due to the lack of proper phase shift or mechanical wedge. Further activation will lead to burning of the wiring.
Is there a difference in checking the inverter compressor?
Yes, fundamentally. Inverter motors (often found in Samsung or LG) have three terminals of the stator windings, and the resistance between them should be approximately the same. Testing for breakdown on the housing remains similar, but a full diagnosis requires special equipment.
What to do if a short circuit is detected?
Repairing windings in a factory environment is difficult and expensive. In 99% of cases, with a confirmed short circuit or breakdown on the housing, it is required to replacement of the compressor new or contract (used in good condition).