The situation when the refrigerator stops freezing, but it’s warm inside, often confuses the owner. The most common cause of failure is the failure of the compressor motor or the starting relay, which is responsible for starting the engine. Many technicians recommend immediately replacing the entire unit, but experienced diagnosticians know: before buying expensive spare parts, you need to make sure that the problem lies in the “heart” of the unit, and not in the control electronics.
Checking the compressor without a starting relay is an emergency diagnostic method that allows you to understand whether the engine is even able to start and gain speed. This method requires caution as you are working with high voltage 220 volts and exposed contacts. However, if you perform all the steps correctly, you can accurately determine the condition of the windings and the mechanical part of the motor without complex equipment.
In this article we will analyze in detail the algorithm of actions, the necessary tools and precautions. You will learn to distinguish a burnt out motor from a faulty relay, which will save you time and money on unnecessary repairs. Remember that safety comes first here, so you absolutely cannot ignore the rules for working with electricity.
Preparation for diagnostics and necessary tools
Before you begin any manipulations with the electrical part of the refrigerator, it must be completely disconnected from the network. Unplug the plug from the socket and provide access to the rear wall of the unit. You will need to remove the protective cover, which is usually secured with screws or plastic clips. Under it you will see the compressor itself and a small black box - this is the starting relay with a thermal release.
To carry out high-quality diagnostics, you will need a minimum set of tools. First of all, you need multimeter (tester) to measure the resistance of the windings. Without it, it is impossible to check the integrity of the circuit. Also have a flathead screwdriver, pliers, and possibly some electrical tape ready. If you plan to carry out a direct start, do not forget to wear gloves to protect your hands.
Visually inspect the compressor and adjacent tubes. They should not show any traces of oil, severe corrosion or mechanical damage. Pay attention to the condition of the wires going to the relay: melted insulation or blackened contacts may indicate a short circuit.
Visual inspection and initial check of the relay
Before removing the relay from the circuit, make sure that it really requires replacement or testing. Often the problem lies in this small element. Carefully remove the relay from the compressor contacts. It can be held on by latches or a metal bracket. There should be no cracks on the case, and no traces of burning or crumbling ceramics inside.
Shake the relay near your ear. If a ringing or knocking sound is heard inside, it means the trigger mechanism is damaged and requires replacement. However, even a visually intact relay may not work. To finally verify its malfunction, you can try to “ring” it with a multimeter, but as part of our task we will check the motor itself, excluding this element from the circuit.
Inspect the contact pins on the compressor itself. They must be clean, free of oxides and soot. If the contacts are blackened, clean them with fine sandpaper or a file. Poor contact can simulate engine failure, creating a false impression of an open circuit.
Checking the integrity of the windings with a multimeter
The most reliable method of primary diagnosis is measuring the resistance of the windings. There are usually three contacts on the compressor housing, forming a triangle. Two of them are the ends of the working and starting windings, and the third is the common terminal. To take measurements, switch the multimeter to resistance measurement mode (Ohm) to a limit of 2 kOhm.
Find the common contact. Usually it is located separately from a couple of others or is marked C (Common). The resistance between the common contact and the working terminal should be minimal, and between the common and starting terminals it should be average. The total resistance between the working and starting terminals should be equal to the sum of the two previous values. If the device shows infinity (open circuit) or zero (short circuit), the compressor is faulty.
It is also important to check the breakdown on the housing. Switch the tester to continuity mode or to the maximum resistance limit. Touch any contact with one probe, and touch the cleaned area on the compressor housing (where there is no paint) with the other. The device should be silent. If a squeak is heard or the readings differ from infinity, it means that the winding is broken into the housing, and it is dangerous to operate such a unit.
Below is a table with approximate values resistance values for various types of compressors, often found in domestic refrigerators:
| Compressor type | Working winding resistance (Ohm) | Starting winding resistance (Ohm) | Probable fault |
|---|---|---|---|
| Low voltage (R600a) | 15 - 25 | 30 - 50 | Normal |
| Medium temperature (R134a) | 20 - 40 | 40 - 80 | Normal |
| Any type | 0 or ∞ | 0 or ∞ | Open or short circuit |
| Any type | Any value | Any value | Breakdown to the housing (if there is current) |
Method of direct start of the compressor
If measurements with a multimeter showed normal resistance values, but the motor does not start through the standard relay, you can try to start it directly. This method allows you to check the mechanical part of the engine and the ability of the rotor to come into motion. To do this, you will need a piece of wire with a plug and, preferably, a button for briefly closing the circuit.
Determine the terminals of the windings. The working winding has less resistance, the starting winding has more resistance. The connection diagram is simple: one wire from the network (phase) is connected to a common contact. The second wire (zero) goes to the working terminal. To start, you need to briefly apply voltage to the starting winding, simulating the operation of the starting relay.
☑️ Safe start of the compressor
Be extremely careful: at the moment If voltage is applied to the starting winding, the compressor may jerk sharply or make a loud sound. Hold the wires securely, but do not touch live metal parts. If the motor starts, it will run smoothly, without strong vibration and hum.
⚠️ Attention: Do not keep the starting winding energized for more than 1-2 seconds. Prolonged supply of current only to the starting winding will lead to its burnout, since it is not designed for constant operation.
Analysis of engine operation and diagnostics of jamming
Successful starting of the compressor does not guarantee its full serviceability. It is necessary to evaluate the nature of his work. A serviceable motor runs quietly, with a uniform hum. If you hear metallic clanging, knocking or loud noise, this may indicate damage to the valve group or bearings.
Check the outlet pressure. To do this, you can carefully (observing safety precautions) place your finger near the outlet of the discharge pipe. When the compressor is running, air under pressure should come out from there. If there is no pressure and the engine is humming, the piston rod may have broken or the valves have been damaged.
What to do if the compressor starts and immediately turns off?
If the motor starts, runs for a few seconds, and then stalls or the thermal protection is triggered, this may indicate a jammed mechanism or an interturn short circuit. Also, the cause may be low voltage in the network or a malfunction of the thermal relay, which you have not yet checked.
Pay attention to the temperature of the case. During the first minutes of operation, the compressor may become slightly warm, but it should not become too hot to touch. Excessive heating indicates overload, friction of parts or problems with cooling.
Typical errors and precautions
The most common mistake is ignoring electrical safety rules. Working with 220 volts requires concentration. Never carry out diagnostics while standing on a wet floor or holding grounded objects (pipes, refrigerator body) with your other hand. This can lead to electric shock.
Another mistake is trying to start the compressor without making sure that the wire insulation is intact. Old wires may have microcracks that could cause an electric shock. Always use a working tool with intact handle insulation.
⚠️ Attention: If, after starting the compressor, you smell burning insulation or see sparking, immediately turn off the power. Continued operation of such a unit may result in a fire.
Do not attempt to repair a hermetic compressor at home. If diagnostics show that the problem is internal (jamming, breakdown of windings), such a unit must only be replaced. Opening the housing requires special equipment and skills, as well as subsequent evacuation and refrigerant charging.
When a compressor replacement is necessary
If all the tests performed indicate a motor malfunction, you should not delay replacement. Signs that require replacement: break or short circuit of the windings, breakdown in the housing, mechanical knocking inside, lack of pressure at the outlet when the engine is running. In these cases, repair is not economically feasible.
When choosing a new compressor, pay attention to the model of the old one. They must match the type of refrigerant (freon R134a or isobutane R600a), power and overall dimensions. Installing a more powerful or less powerful motor will disrupt the operation of the refrigeration system as a whole.
Remember that replacing a compressor is a complex process that requires tools for working with copper tubes (torch, rolling) and a vacuum pump. If you do not have experience and equipment, it is better to entrust this work to a professional technician.
Is it possible to check a compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without a device. However, if, when connected directly (via a working relay or manually), the compressor hums and vibrates, but does not start, and a click is heard, most likely the problem is in the relay or the starting winding. If there is complete silence, a break is likely.
Why does the compressor hum, but does not start?
This is a classic symptom of a faulty start relay or jammed piston group. Also, the reason may be an interturn short circuit, when the engine tries to start, but it lacks power due to damage to the winding.
Is it dangerous to leave a refrigerator with a faulty relay?
Yes, it is dangerous. A faulty relay may not turn off the starting winding, which will lead to its burnout and fire. In addition, constant attempts to start wear out the compressor. If the relay is faulty, it must be replaced or the unit must be temporarily disconnected from the network.
How much does it cost to replace a compressor?
The cost consists of the price of the unit itself and the work of the technician. On average, taking into account materials and freon charging, repairs can cost 40-60% of the cost of a new refrigerator. Numbers may vary depending on the region and model of equipment.