Sudden silence of the refrigerator or, conversely, its humming but inoperative compressor is always stressful, because the safety of food and the comfort of the household are at stake. When you hear clicks of the start relay, but it is silent, there is a natural desire to check its performance, eliminating faults in the electrical control circuit. unit is silent, there is a natural desire to check its performance, eliminating malfunctions in the electrical control circuit. Direct start motor is an effective diagnostic method that allows you to determine with a high degree of probability whether the compressor itself is alive or the problem lies in the start-protection relay, thermostat or wiring.
However, before you take up the tools, you must clearly understand: working with 220 volt electricity requires extreme concentration and compliance with safety precautions. If traces of oil or mechanical damage are visible on the compressor housing, it is strictly prohibited to start itas this can lead to a short circuit or fire. In this article we will analyze in detail the algorithm of actions, the necessary tools and nuances that will help you correctly diagnose the condition of the heart of your refrigerator.
Preparation for diagnostics and the necessary tools
Any serious Diagnostics begins with ensuring safe working conditions. You will need access to the back of the refrigerator where the motor-compressor is located. The first step is to completely de-energize the device by unplugging the plug from the socket. Do not rely only on turning off the thermostat; a physical break in the power circuit is required for your safety.
To conduct a quality check, you will need a minimum set of tools, which are often already in the arsenal of a home craftsman. The main device will be a multimeter (tester) capable of measuring resistance and circuit integrity. You will also need screwdrivers for dismantling the casing, pliers and, possibly, electrical tape.
It is important to prepare the workplace in advance, providing good lighting, since the compressor niche is often dark and cramped. If you plan not just to ring the windings, but to start the motor, you may need a special diagnostic plug or wires with clamps to temporarily connect power, bypassing the standard relay.
Be sure to check the condition of the wires going to the compressor. If the insulation is cracked or melted, it is dangerous to work with such equipment without first replacing the harness. Insulation integrity —the first indicator of whether there has been overheating or a short circuit in the past.
☑️ Preparation for inspection
Visual inspection and dismantling the starting relay
Before proceeding to electrical measurements, a thorough visual inspection of the unit should be carried out. The compressor is usually enclosed in a metal or plastic casing that is secured with bolts or latches. Carefully remove the protection, being careful not to damage the tubes and wires.
The focus will be on the starting relay - a plastic box placed on the compressor terminals. It is this element that most often fails, simulating an engine breakdown. Carefully remove the relay by disconnecting it from the motor contacts and disconnecting the appropriate wires.
⚠️ Attention: On some refrigerator models, the relay may be secured with a clamp or have specific latches. Do not use excessive force to avoid breaking the plastic mounting ears, which are difficult to repair.
Inspect the removed relay for external defects. A burning smell, blackened plastic or traces of melting inside the case eloquently indicate that the element has overheated. If the relay looks suspicious, there is a high probability that it is to blame for the refrigerator stopping, and the engine is working. Pay attention to the copper contacts on the compressor itself. They must be clean, free of oxides and soot. If you see traces of soot, carefully sand them off with fine sandpaper before further inspection. Oxides create a high contact resistance that interferes with normal starting.
Pay attention to the copper contacts on the compressor itself. They must be clean, free of oxides and soot. If you see traces of soot, carefully sand them off with fine sandpaper before further inspection. Oxides create high contact resistance, which interferes with normal starting.
Why does the relay burn out?
A common reason for the starting relay burning out is an attempt to start the compressor when the network voltage is low or when the piston group is jammed. The relay tries to start the motor, the current increases, and the thermal protection does not have time to operate, causing overheating of the contacts.
Testing the windings with a multimeter
The most reliable method of primary diagnosis is checking the electrical resistance of the stator windings. On the case of most compressors there is a diagram or marking of the terminals (C, S, R), but it is better to focus on their location in a triangle. You need to find paired terminals corresponding to the starting and working windings.
Switch the multimeter to resistance measurement mode (Ohms). Place the probes on the contacts. Normal readings for a working engine vary within the following limits: the resistance of the starting winding is usually higher (from 20 to 50 Ohms), and the working winding is lower (from 10 to 15 Ohms). The total resistance between the extreme contacts should be equal to the sum of the resistances of the individual windings.
If the device shows infinity (open) or zero (short circuit), this indicates an internal malfunction of the motor. In the event of a break, the current simply does not flow, and in the event of a short circuit, instant heating occurs and the plugs are knocked out. It is also important to check the breakdown on the housing.
To check the breakdown, one multimeter probe is applied to any copper fitting or stripped part of the compressor housing, and the second is applied to the contacts in turn. The device should show infinity. Any resistance value indicates that the winding insulation is broken and the current goes to ground.
| Measurement type | Normal readings | Fault symptom | Probable cause |
|---|---|---|---|
| Working winding | 10 - 15 Ohm | Infinity or 0 Ohm | Open or interturn short circuit |
| Start winding | 20 - 50 Ohm | Significantly higher than normal | Contact burnout or breakage |
| Breakage to the body | Infinity (∞) | Any numerical value | Destruction of insulation, life-threatening |
| Thermal relay | 0 Ohm (closed) | Infinity (cold) | Bimetallic plate burned out |
Direct start technology of the compressor
If a check with a multimeter shows that the windings are intact and there is no breakdown on the housing, but the refrigerator does not work, the direct start stage begins. This action allows you to exclude all control elements (thermostat, relays, defrost sensors) from the circuit and apply voltage directly to the motor.
To do this, you will need to assemble a temporary circuit. You need to apply 220 volts to the common contact and the working terminal, and short-circuit the starting winding through a capacitor or button, simulating the operation of a starting relay. Be extremely careful: all contacts must be reliably insulated, keep your hands away from live parts.
Apply power. A working engine should start with a characteristic hum. If a hum is heard, but the shaft does not spin, and after a few seconds the machine knocks out, the piston group may have jammed or there has been a turn in the winding that is not visible when dialing.
If the compressor starts and runs smoothly, let it run for 1-2 minutes. Check the heating of the case (it should heat up evenly and moderately) and listen to the sound. Extraneous knocking, clanging or metallic grinding sounds indicate mechanical wear of the components, which requires replacement of the unit.
Analysis of results and typical errors
After diagnostics, it is important to correctly interpret the data received. Often, amateur craftsmen make mistakes, considering a motor that just “twitched” to be serviceable. The actual working stroke should be confident, without frantic attempts to start.
A typical mistake is to ignore the condition of the oil. If, during direct start, black smoke or oil with soot escapes from the compressor tubes, this is a sign that insulation or freon was burning inside the engine. Such a unit will not last long and can contaminate the entire cooling system.
It is also worth considering that some modern inverter compressors cannot be checked are directly connected to a 220V network. They are controlled by special boards that supply current at a certain frequency. Direct supply of voltage to the inverter motor can instantly disable it.
⚠️ Attention: Inverter compressors (often found in the latest generation LG, Samsung, Bosch refrigerators) can only be diagnosed through a special tester or by replacing the control board. Direct supply of 220V is disastrous for them.
If after starting the compressor works, but does not cool, the problem may not be in the electrics, but in a freon leak or a clogged capillary tube. In this case, the engine is operational, but the system does not perform its thermochemical function.
Frequently asked questions about diagnostics of refrigerators
Is it possible to restore the compressor if it is jammed?
There is a method of “wedging” by applying increased voltage or hitting the housing when running motor, but the effectiveness of this method at home is low (about 10%). Most often, jamming means physical destruction of the friction pairs, and it is easier to replace such a unit with a new one.
Why does the compressor start and immediately turn off?
This is the thermal protection relay triggered. Reasons: overheating of the windings due to an interturn short circuit, lack of refrigerant (freon) that cools the motor, or a malfunction of the relay itself. It is also possible that the pressure in the condensation system is too high.
Is it dangerous to leave a running compressor without a cooling system?
Yes, it is dangerous. The compressor is designed for cooling by freon vapor and oil circulating in the system. Working “dry” or in an open circuit for more than 5-10 minutes can lead to overheating and deformation of the valves, even if it is electrically intact.
How to distinguish an inverter compressor from a conventional one?
Inverter models are usually quieter, do not have clicks when turning on/off (they work constantly, changing power) and are often marked "Inverter" on the case. The main difference is the presence of an electronic control board attached directly to the motor or located nearby.