If your refrigerator stops freezing, but there is silence inside or, conversely, a hum is heard without cooling, most likely the problem lies in the heart of the system - compressor. This unit is responsible for circulating the refrigerant, and its failure leads to food spoilage. Before calling a technician or buying new equipment, it is worth carrying out an initial diagnosis to understand the scale of the disaster.
Often, owners of equipment immediately blame the motor, although the reason may be more trivial: the starting relay has burned out or there has been a power surge. Checking the compressor yourself allows you to save a significant amount if it turns out that the motor OK, but the problem is in the electrical circuit. However, if the engine really fails, knowing the symptoms will help you make an informed decision about repairs.
In this article we will analyze in detail the algorithm of actions for diagnosing the motor-compressor in various ways. You will learn what tools are needed, how to safely disassemble the equipment and how to interpret instrument readings. Attention: any work with electrical appliances requires compliance with electrical safety rules.
⚠️ Attention: Before starting any diagnostic work, be sure to disconnect the refrigerator from the electrical network. Working with live current is deadly.
Primary visual diagnosis and symptom analysis
The first thing to do is listen to the operation of the unit. If the refrigerator hums, but there is no cold, or the motor starts for a couple of seconds and immediately clicks, turning off, these are classic signs of a malfunction. Normally, the compressor should work cyclically: turn on, gain speed, work for a certain time and turn off. A constant hum without cooling may indicate a freon leak or a blockage in the system, and not necessarily the death of the motor itself.
Inspect the back wall of the refrigerator. If you see oily spots in the compressor area, this is a bad sign. Oil there should not be any circulation in the system, it is located in the engine crankcase. Its appearance on the outside indicates depressurization of the housing, which often leads to jamming of the piston group. In this case, repair is most often impractical.
It is also worth paying attention to the temperature of the compressor housing itself. If after trying to turn it on it remains cold, it means that the windings are not receiving power or there is an open circuit. If it becomes red-hot or to temperatures that cannot be touched, and does not start, there is an interturn short circuit or a wedge in the mechanism.
Necessary tools for testing
For high-quality diagnostics, you will need a minimum set of tools that any home craftsman can find. The main device will be multimeter (tester), which allows you to measure resistance and test circuits. Without it, the check will only be of a guessing nature, since it is impossible to visually determine the integrity of the windings.
In addition to the multimeter, you will need screwdrivers (Phillips and flathead) to remove the casing, pliers for working with terminals and, possibly, electrical tape. If you plan to test start the motor directly, bypassing the standard relay, you will need a separate wire with a plug or a special test cord with a button.
It would be a good idea to prepare a clean rag and, if necessary, WD-40 to clean the contacts from oxides. Oxidized terminals may produce false resistance, leading to incorrect conclusions about the condition of the motor. Also have a notepad on hand to write down the color coding of the wires before disconnecting them.
Removing the compressor and accessing the contacts
To get there To access the electrical part of the motor, you must remove the protective cover at the lower rear of the refrigerator. It is usually secured with latches or bolts. Carefully unscrew the fasteners and remove the metal or plastic cover, being careful not to damage the tubes and wiring.
Inside you will see a black barrel - this is the compressor. A start-up relay and a thermal relay are attached to its lower part. It is this box that needs to be carefully removed. It is simply put on three pins coming out of the motor housing. Important: do not pull sharply so as not to break off the contacts or damage the fragile tubes.
After removing the relay, three triangle-shaped contacts will open in front of you. These are the winding terminals. On some models they may be marked, but most often there is no marking, and you have to navigate by their location and the color of the wires coming from the relay. Before checking, it is advisable to clean the contacts from carbon deposits or oxidation.
Checking the integrity of the windings with a multimeter
The most reliable diagnostic method is measuring resistance the windings. Switch the multimeter to resistance (ohms) measurement mode. First, check for a breakdown on the housing: attach one probe to any contact, and the other to the cleaned metal part of the compressor housing (where there is no paint). If the device shows “infinity” (number 1 or OL), then there is no breakdown. If there are any values, the motor is faulty and requires replacement.
Next, we measure the resistance between the contacts. A standard single-phase motor has three terminals: common (C), starting (P) and working (P). The resistance between them must fit within certain norms. Typically, the sum of the resistances of the starting and working windings is equal to the resistance between the extreme contacts. Typical values: operating winding 10-30 Ohm, starting winding 20-50 Ohm.
If the device shows zero (0) between any contacts, this indicates a short circuit of the turns. If the device shows infinity, it means there is a break in the winding. In both cases restoration of the compressor at home it is impossible, it needs to be replaced.
| Measurement type | Normal value | What does deviation mean |
|---|---|---|
| Continuity to the body | Infinity (∞) | Insulation breakdown, life-threatening |
| Working winding | 10 - 35 Ohm | Open (∞) or short circuit (0) |
| Start winding | 20 - 50 Ohm | Open (∞) or short circuit (0) |
| Resistance between extremes | Sum of two others | Incorrect circuit or burnt contact |
Diagnostics of the starting relay and thermal protection
Often the “hero” of the occasion is not the engine itself, but its starting system. The starting relay is responsible for supplying an impulse to the starting winding at the moment of start. Inside it there is a coil and contacts that can burn. Disassemble the relay housing (usually it has latches) and inspect the contacts. If they are black or melted, the relay needs to be changed.
Thermal protection (bimetallic plate) is used to turn off the motor when it overheats. Check it with a multimeter in dial mode. When cold, it should ring (show zero or a value close to it). If the circuit does not close, the protection is faulty and requires replacement. This is a cheap part, but without it the motor can burn out if overloaded.
It is also worth checking the capacitor if your model has one (usually in older refrigerators or powerful models). It must hold a charge. However, more often than not, modern household refrigerators use a starter coil circuit without an external capacitor, and all the magic happens inside the black plastic relay block.
⚠️ Attention: Do not try to repair the start relay by gluing the contacts together or cleaning them with sandpaper. This is a temporary measure that may cause a fire. Replace the unit with a new one with the same marking.
☑️ Checking the relay and protection
Test start of the motor directly
If the windings are intact and the relay is working, but the refrigerator is not works, you can try to start the compressor directly, bypassing the standard automation. To do this you will need a cord with a plug. We connect one end of the wire to the common contact, the other to the working one. The launch should happen immediately. If the motor hums and runs, the problem is in the relay.
Be careful: with this connection, the motor is not protected from overheating and current surges. You cannot keep it turned on for a long time; 5-10 seconds are enough to make sure that the rotor is working. If the engine hums, jerks, but does not spin, the piston group may be jammed.
Sometimes “wedging” with a blow helps, but this is a last resort. Some craftsmen try to apply increased voltage or use a special block for wedging, but at home this is risky. If the motor does not start even when directly connected to a working 220V network, it must be disposed of.
Is it possible to restore a jammed compressor?
There is a method of supplying 380V voltage to a three-phase motor (converted) or using special transformers for a “jerk”, but (the probability of success) is less than 30%. Most often, such a motor does not work for long and requires an oil change and evacuation of the system, which cannot be done at home.
Frequent diagnostic errors
Beginners often confuse the symptoms of a freon leak with a compressor failure. If the motor runs constantly without turning off and the cooling is weak (or only the freezer), most likely there is a leaked refrigerant. The compressor has nothing to do with it, it is simply trying to compensate for the lack of refrigerant by constant operation.
Another mistake is ignoring the condition of the wiring. Oxidized wires at the junction with the relay can create a high contact resistance, which is why the motor does not receive the required current to start. Always check not only the parts, but also the electrical supply routes.
Do not forget about the climate class of the refrigerator. If you try to start a refrigerator designed for a temperate climate (SN, N) in an unheated garage in winter at a temperature of +5 ° C, it may not turn on at all due to the oil solidifying or the thermostat. This is not a breakdown, but a feature of operation.
⚠️ Attention: Technical characteristics and circuitry may vary depending on the manufacturer and year of manufacture of the model. Always check the official documentation or electrical diagram pasted on the body of your device.
Frequently asked questions (FAQ)
How many ohms should be on the refrigerator compressor?
The normal resistance of the working winding is usually 10–35 Ohms, the starting winding is 20–50 Ohms. The exact values depend on the motor power. The main rule: the resistance between the common and working contacts plus the resistance between the common and starting contacts must be equal to the resistance between the working and starting contacts.
Why does the compressor hum but does not start?
This may indicate several problems: jamming of the piston group, a malfunction of the starting relay (does not send a pulse to start) or interturn short circuit in the windings. Also, the reason may be low voltage in the network.
Is it possible to change the compressor yourself?
Theoretically, yes, but this requires special equipment: a vacuum pump, a pressure gauge station and a torch for soldering copper tubes. You can’t just “over-twist” the motor; the system needs to be evacuated and filled with freon strictly by weight.
How to determine which wire goes where if there is no marking?
You need to ring all three contacts together. The pairs with the highest resistance are the working and starting terminals. The third contact, which remains free (or has the least resistance when paired with others), will be common. The working winding always has less resistance than the starting winding.