How to check a refrigerator compressor at home

The sudden stop of the refrigerator or the appearance of extraneous sounds often becomes an unpleasant surprise for the owner of household appliances. In most cases, the cause of the breakdown is precisely compressor the heart of the refrigeration unit, which is responsible for the circulation of the refrigerant. Self-diagnosis of this unit allows you to save significant money on calling a technician and avoid purchasing unnecessary spare parts if the problem lies elsewhere.

Before you start disassembling and taking measurements, you need to understand the basic principle of the motor. It converts electrical energy into mechanical energy by compressing freon gas and pumping it into a condenser. If electric motor does not start, hums without rotating the shaft, or turns off immediately, this indicates serious problems with the electrical or mechanical part. It is important not to panic and to consistently perform a series of testing steps in order to accurately determine the nature of the malfunction.

In this article we will analyze all available diagnostic methods, from simple visual inspection to accurate measurements of winding resistance using a multimeter. You'll learn how to differentiate a burnt out motor from problems with the start relay or thermostat. A competent approach to diagnosis will help you make an informed decision: repair an old unit or think about buying a new one.

Initial visual examination and analysis of symptoms

Any professional diagnostics begins with a careful study of external signs. Don’t rush to grab your tools, first turn on the refrigerator and listen. If the unit is silent and the light inside is on, this already narrows the range of possible causes. The absence of the characteristic hum of the compressor when the lighting is running often indicates a lack of voltage on the motor itself, which may be due to an open circuit or a malfunction of the thermostat.

Pay attention to the behavior of the motor in the first seconds after switching on. If you hear a quiet click followed by a hum that lasts 5-10 seconds, followed by another click and silence, this is a classic symptom of a starting attempt. In such a situation start relay the current is supplied, the engine tries to turn over, but due to mechanical jamming or interturn short circuit it fails. The thermal relay is activated, opening the circuit, and the cycle is repeated after a while.

⚠️ Attention: If you smell burning plastic or see sparking in the compressor area, immediately unplug the refrigerator. Further experimentation may result in fire or electric shock.

A visual inspection of the rear of the unit is also important. Look for signs of oil, soot, or swelling. The presence of oily spots under the compressor may indicate depressurization of the system, which is often accompanied by a freon leak. In this case, even an electrically functional motor will not be able to provide cooling, since there is no working fluid in the system to transfer heat.

Necessary tools for checking the motor

To properly check the technical condition of the compressor, you will need a minimum set of tools, which many home craftsmen can find. The main device will be multimeter (tester), which allows you to measure the resistance of the windings and check the integrity of the circuit. Without this device, accurate diagnostics of the electrical part is practically impossible, since it is impossible to determine the interturn short circuit by eye.

In addition to the measuring device, you will need screwdrivers to remove the protective casing at the bottom of the refrigerator. Typically a Phillips and flat head screwdriver is required. It would also be a good idea to have pliers to carefully remove the terminals and electrical tape for marking the wires if you plan to disconnect them. To check the mechanical part, a pressure gauge manifold is sometimes used, but at home you can do without it, relying on indirect signs.

It is important to ensure good lighting of the work area, since the compressor niche is often dark and cramped. If you don't have a built-in light, use a flashlight or headlamp. All work must be carried out with the power supply disconnected from the mains to eliminate the risk of electric shock.

Checking the serviceability of the starting and thermal relay

Before sinning on the engine itself, it is necessary to exclude a malfunction of the starting device. It is the relay that supplies the initial impulse to start the rotor and protects the motor from overloads. In modern refrigerators, posistor relays are most often found, in older ones - induction. Checking them is a mandatory step, since they fail even more often than the compressor itself.

Remove the plastic relay housing by disconnecting it from the compressor contacts. Visually inspect the insides: if the inside is blackened, the plastic has melted or there is a burning smell, the part needs to be replaced. To more accurately check the posistor, you can use a multimeter in resistance measurement mode. A working posistor at room temperature should have a low resistance, usually within a few tens of ohms.

The thermal relay also plays a critical role. It opens the circuit when the windings overheat. If its contacts are oxidized or the mechanism is jammed, the current simply will not reach the engine. Check the continuity of the circuit through the thermal relay: if the device shows infinity (open), it means that the circuit is open and the motor will not start. Replacing these components is inexpensive and often solves the problem of a “non-working” refrigerator.

How to distinguish a posistor relay from an induction relay?

A posistor relay is usually made in the form of a small black cylinder or cube inside a plastic case. An induction relay has a more complex design with a coil and a moving core, often in a metal or larger housing. PTC models are more reliable and common in technology over the last 20 years.

Diagnostics of compressor windings with a multimeter

This is the most critical stage of testing, allowing you to determine the condition of the electrical part of the engine. First you need to remove the terminal block from the three contacts of the compressor. Usually they are marked with letters or symbols: S (Start) - starting winding, R (Run) - working winding and C (Common) - common wire. Sometimes numbers or dots are used instead of letters, so it is better to check the technical documentation for the specific model of the refrigerator.

Turn the multimeter into resistance measurement mode (Ohm) to a limit of 2 kOhm. First check the resistance between pairs of contacts. Measure the resistance between the common contact and the operating winding, then between the common and starting windings. The third measurement is made between the starting and operating windings. The sum of the first two measurements should be approximately equal to the third. This is the basic law of physics for such motors.

Then you need to check the windings for breakdown on the housing. Switch the tester to the “continuity” mode or to the maximum resistance limit (Megaohms). With one probe, touch the cleaned area on the compressor housing (where there is no paint), and with the other, touch all three contacts one by one. The device should show infinity. If you see any resistance values, this means that the insulation is broken and current is flowing to the housing, which is dangerous and requires replacing the unit.

Below is a table with approximate resistance values ​​for serviceable compressors of various capacities. Remember that the exact numbers may vary depending on the manufacturer and model.

Checking the mechanical part and pressure

If the electrical part is in order, but the refrigerator does not freeze, the problem may lie in the mechanics. The compressor may be electrically functional, but not produce the necessary pressure to circulate freon. This often happens when the piston group or valves wear out. At home, it is difficult to check the pressure without a pressure gauge, but you can use an indirect method.

Carefully disconnect the capillary tube or compressor outlet pipe (after bleeding off the freon if the system is not empty, although for a simple check they often simply bend the tube). When turned on, a working motor should create a noticeable stream of air at the outlet. If you bring your finger to the hole and do not feel a confident pressure, but only a weak hiss, the compressor “does not pump.”

⚠️ Attention: If the integrity of the refrigeration circuit is damaged, refrigerant enters the atmosphere. Although modern freons (R600a, R134a) are relatively safe, R600a is explosive in concentration. Work in a ventilated area and avoid open flames.

Another sign of mechanical failure is the nature of the sound of the motor running. A serviceable unit operates smoothly, with moderate vibration. If you hear a metallic clanging, knocking or grinding sound, this indicates destruction of the internal mechanisms, engine suspension, or solid particles entering the compression chamber. In such cases repair is impossible, a complete replacement of the unit is required.

Frequent errors during self-diagnosis

Many refrigerator owners make typical mistakes, trying to save money on diagnostics. One of the most common is replacing the compressor without checking the start relay and thermostat. As a result, a new expensive unit may burn out in the very first minutes of operation or simply not start, since the reason was in the control circuit and not in the engine.

Another mistake is ignoring the wiring condition. Oxidized contacts, burnt terminals or frayed wires can create high contact resistance, causing the motor to not receive enough voltage to start. Always check the integrity of the wires running from the outlet to the compressor itself.

Also, do not forget about the temperature regime. It is better to check the winding resistance on a cold engine. If the compressor has just been running, the resistance may be higher than rated due to heating of the copper. Allow the unit to cool for 30-40 minutes before taking measurements to obtain correct data.

Is it possible to start the compressor directly without a relay?

Technically, you can start the motor by applying voltage directly to the working and starting windings for a short time. However, this method is dangerous: without thermal protection, the motor can burn out in a few seconds if it jams, and the risk of electric shock is very high. Use this method only for experienced craftsmen in compliance with all safety measures.

Frequently asked questions (FAQ)

Which multimeter is best to use to check a refrigerator?

For home diagnostics, any digital multimeter with a resistance (Ohm) and circuit continuity measurement mode is suitable. The accuracy of the device is not critical; the main thing is the serviceability of the probes and battery. Expensive professional clamps for measuring starting currents in everyday life are usually not required.

What to do if the resistance of the windings is normal, but the refrigerator does not turn on?

If the electrics are in order, the problem may be in the thermostat (temperature sensor), which does not give the command to turn on, or in the electronic control module. It is also worth checking the integrity of the supply cable and the outlet itself. Perhaps the overload protection in the electrical network has tripped.

Is it possible to repair a burnt-out compressor?

In a factory setting, rewinding the motor is possible, but at home it is not practical. The cost of labor and spare parts will exceed the price of a new compressor. In addition, after opening the case, the system must be evacuated and charged, which requires special equipment. It’s easier and more reliable to buy a new unit of the same power.

Why does the new compressor hum louder than the old one?

Modern models can operate louder due to design features or higher speeds. However, excessive hum, vibration, or clanging noises are not acceptable. Make sure that the compressor is correctly installed on the shock absorbers and does not touch the walls of the niche or pipes. Sometimes it is necessary to replace vibration isolating bushings.