The situation when the refrigerator stops freezing, but it becomes warm inside, often takes you by surprise. In most cases, the first suspicion is a failure compressor, which is the “heart” of the entire cooling system. However, before calling a technician or buying a new unit, it makes sense to carry out independent diagnostics in order to accurately understand the cause of the breakdown.
Checking a motor-compressor is a process that requires care and compliance with safety precautions, but it is quite within the capabilities of a person with minimal skills in handling electrical appliances. Knowing how to call windings and check resistance will help you avoid unnecessary expenses on repairing serviceable components or, conversely, will confirm the need for a complex replacement.
In this article we will analyze in detail the diagnostic algorithm, the necessary tools and typical mistakes that beginners make. Correct assessment of the condition of the electrical part of the engine is the key to successfully restoring the functionality of your equipment.
Main signs of a compressor malfunction
Before disassembling the back panel of the refrigerator, it is necessary to analyze the symptoms that the device exhibits. Often, external signs may indicate a problem with the start relay or thermostat, but the engine itself remains fine. Understanding these differences saves time and effort.
One of the most obvious signals is a characteristic click, after which the refrigerator hums for several seconds and then goes silent. This is the classic picture of a starting attempt where start relay triggers but the engine cannot spin due to a wedge or electrical fault. If at the same time the motor housing gets very hot and the inside of the chamber is warm, the problem is most likely in the power unit.
It is also worth paying attention to the operation of the refrigerator as a whole. If it turns on, runs continuously without turning off, but does not reach the desired temperature, this may indicate a loss of compressor performance or a freon leak. Unlike electrical breakdowns, mechanical wear of the piston group is more difficult to diagnose and often requires replacement of the unit.
- 🔊 The refrigerator hums, clicks and immediately turns off.
- 🔥 The compressor housing overheats (above 80-90 degrees).
- ❄️ The unit works constantly, but does not freeze.
- ⚡ The automatic switch in the panel is triggered when the refrigerator is turned on.
It is important to note that the absence of a sound from the compressor when the refrigerator is plugged in and the light bulb inside the chamber is on indicates a broken circuit. This could be either a burnt winding or a malfunction of the control electronics or thermostat.
Necessary tools and safety measures
Diagnostics of refrigerator electrical circuits is impossible without a basic set of tools. The main device here is multimeter (tester), which allows you to measure the resistance and integrity of the circuit. Without it, any manipulations will be in the nature of fortune telling on coffee grounds.
⚠️ Attention: Before starting any work on diagnosing the compressor, be sure to disconnect the refrigerator from the electrical network! Working with live electrical appliances is deadly.
In addition to a multimeter, you will need a set of screwdrivers to remove the protective casing at the bottom of the refrigerator. Some models may require pliers to remove the contacts. Make sure that the workplace is well lit and your hands are dry.
The condition of the wires deserves special attention. If you see melted insulation, blackened contacts, or smell a burning smell, this is a direct indication of an overload or short circuit. In such cases, a simple test may not be sufficient, and replacement of damaged wiring elements will be required.
- 🛠️ Multimeter (analog or digital).
- 🔧 Set of screwdrivers (Phillips and flathead).
- 🔦 Flashlight for illuminating hard-to-reach areas places.
- 🧤 Dielectric gloves (recommended).
If you do not have a multimeter, you can use the simplest control (a light bulb with two wires), but it will only show the presence of voltage or the integrity of the circuit, without giving accurate data on the resistance of the windings. For professional diagnostics, it is better to purchase even an inexpensive digital tester.
Dismantling and visual inspection of the unit
To get to the compressor, you need to turn the refrigerator over or gain access to its lower part. In modern models, it is often enough to remove the back panel in the lower third of the case. Old Soviet refrigerators sometimes require moving completely away from the wall and access from the rear.
After removing the protective casing, you will see a black barrel - this is the compressor. Electrical wires and copper pipes of the refrigeration circuit are suitable for it. First of all, do a thorough visual inspection. Look for traces of oil that may have leaked from the system, or signs of rust on the motor housing.
Pay special attention to the place where the wires are connected - the starting relay. It is usually attached directly to the compressor terminals. If the relay shows signs of burning, cracks or melted plastic, there is a high probability that the problem lies in this unit, and not in the engine itself.
To remove the relay, it is usually enough to simply press out the fixing brackets or carefully disconnect it from the compressor terminals. Do not use excessive force as plastic parts become brittle over time. If the relay is removed, inspect the inside: the contacts should not be oxidized or burnt.
How to test the windings with a multimeter
The most reliable way to check an electric motor is to measure the resistance of its windings. On the housing of most compressors there is a diagram or marking of the terminals, but even if there is none, the testing principle is the same for all single-phase motors. You need to find three contacts: common, starting and working.
Switch the multimeter to resistance measurement mode (Ohm). First, check the continuity of the circuit to the housing to exclude an insulation breakdown. Press one probe against any copper fitting (tube) or stripped part of the body, and with the other touch each of the three contacts in turn. The device should show infinity (or “1” on the digital screen). If you see any resistance values, it means that something has happened breakdown to the housingand such a compressor cannot be operated.
Next we move on to checking the continuity of the windings themselves. There should be three resistance values between the three terminals. The sum of the two smaller resistances must equal the largest. Typically, the greatest resistance is the sum of the starting and operating windings. The working winding has a lower resistance (usually 10-30 Ohms), and the starting winding has a higher resistance (30-50 Ohms), although the values may differ in different models.
| Measurement type | Normal reading | Fault |
|---|---|---|
| Winding to the body | Infinity (∞) | Any number (breakdown) |
| Working winding | 10 - 30 Ohm | 0 (short circuit) or ∞ (break) |
| Start winding | 30 - 50 Ohm | 0 (short circuit) or ∞ (break) |
| Sum of windings | Equal to total resistance | Sum mismatch |
If the multimeter shows zero (0) on any of the windings, it means short circuit turns. If the device shows infinity, it means the circuit is in break. In both cases, the compressor is considered faulty and requires replacement. Repairing the windings at home is impossible due to the tightness of the housing and the difficulty of rewinding.
☑️ Checking the windings
Diagnostics of the starting relay and thermal protection
Often the reason that the compressor does not start is not the motor itself, but its wiring. The starting relay is responsible for briefly applying voltage to the starting winding to spin the motor shaft. Thermal protection (thermal relay) opens the circuit when overheated, saving the motor from combustion.
The relay is checked by testing its contacts. Depending on the design (posistor or with a coil), the principle may differ. PTC relays often fail due to the destruction of the ceramic element. If you shake the relay and something rattles inside, or traces of burning are visible, it needs to be changed. The cost of such an element is low, and replacing it often solves the problem.
⚠️ Attention: Starting relays are not universal. When purchasing a new part, be sure to check the markings and connection diagram with the original installed on your refrigerator.
Thermal protection is checked in the same way: in a cold state it should “ring” (show zero or close to it resistance). If the circuit is broken, it means the protection has burned out or lost contact. Sometimes it is enough to simply cool the compressor so that the bimetallic plate inside the protection returns to its original position, but if this happens often, look for the cause of overheating.
Why does the starting relay burn out?
Most often, the relay fails due to attempts to start a “jammed” compressor or power surges in the network. Also, the cause may be poor contact in the connector, which leads to sparking and heating.
If the relay and protection are working properly, but the compressor still does not start, it is worth checking the voltage coming to the relay contacts when the refrigerator is turned on. To do this, you will need to turn on the unit to the network (using maximum caution!) and measure the presence of 220 Volts at the input to the relay. If there is voltage, but there is no start, the problem is in the engine.
Mechanical problems and compressor wedge
Electrical serviceability of the windings does not guarantee that the compressor will work. There is a concept called “mechanical wedge”. This is a condition when the piston group is jammed due to exhaustion, lack of lubrication, or foreign particles entering the system. In this case, the motor hums, trying to turn over, but the shaft stands still.
Sometimes, if the wedge is not strong, you can try to “unwedge” the compressor. To do this, there is a method of applying voltage directly to the working winding, bypassing the starting relay, or briefly applying increased voltage. However, this method is risky and can completely finish off the unit or lead to a fire, so it is recommended only to experienced craftsmen.
Another mechanical problem is a break in the piston rod or valves inside the hermetic unit. In this case, the compressor may work, hum, and even heat up, but not create the necessary pressure in the system. Diagnosing this defect without connecting a manometric manifold (to measure freon pressure) is difficult, but this is indirectly indicated by the lack of cold when the engine is running.
- 🛑 The compressor hums, but does not start (a wedge is possible).
- 📉 The pressure in the system does not rise (faulty valves).
- 🔨 The wedging method is dangerous and does not guarantee success.
- 🔧 For accurate diagnosis of mechanics, you need a pressure gauge.
If you suspect a mechanical breakdown, further self-diagnosis makes no sense. It is necessary to either replace the compressor, or, in case of loss of pressure, search for a refrigerant leak and refill the system, which requires special equipment and a license.
Often asked questions (FAQ)
Is it possible to check a compressor without a multimeter?
Indirectly - yes. You can connect the compressor directly to the network (via a working relay or starting circuit), but this is dangerous and does not provide accurate information about the condition of the windings. Without the device, you will not know whether there is a breakdown to the housing or an interturn short circuit, which can lead to an electric shock or fire.
What resistance is considered normal for a compressor?
Normal values vary depending on the power and engine model. Typically, the working winding has a resistance of 10 to 30 Ohms, and the starting winding has a resistance of 20 to 50 Ohms. The main rule: the resistance between the common contact and the other two should be approximately the same or follow the logic of the sum, and should not go to the housing.
Why is the compressor hot, but the refrigerator does not freeze?
This may indicate several problems: a freon leak (the compressor is running empty), a clogged capillary tube or a loss of performance of the compressor itself (wear of the valves). It is also possible that the air circulation inside the chamber is impaired due to ice.
Is it worth replacing the compressor on an old refrigerator?
Replacing a compressor is an expensive repair, including the cost of a new unit, the work of a technician and refilling with freon. If the refrigerator is more than 10-12 years old, it is often more economically feasible to purchase new equipment, since the resource of other components (evaporator, condenser) may also be running out.