Sudden Stopping the refrigerator or, conversely, its continuous hum often indicates problems with the heart of the unit - the compressor. It is this unit that is responsible for circulating the refrigerant in the system, creating the necessary pressure to cool the chambers. When the motor stops coping with its task, the food begins to deteriorate, and the characteristic heating may disappear on the rear grill or, on the contrary, an ice crust may appear.
Before calling a technician or buying new equipment, it makes sense to carry out the initial diagnostics yourself. Checking the engine does not always require complex equipment, although having a multimeter will greatly simplify the task. Understanding the principles of operation and signs of breakdown will help you avoid unnecessary expenses and accurately describe the problem to a specialist.
In this article we will look at the main methods for assessing the condition of the compressor, from simple listening to electrical measurements. You will learn how to distinguish a malfunction of the motor itself from problems with the start relay or thermostat. Competent diagnostics is the first step to successful refrigerator repair.
Visual and acoustic diagnostics of the condition
The first stage of testing is always an external inspection and analysis of the sounds produced by the unit. A working compressor operates cyclically: it turns on, gains temperature, and turns off. If you hear that the motor is humming constantly without rest breaks, this is an alarming signal. Overheating of the windings in this case, it can lead to thermal breakdown of the insulation.
Pay attention to the nature of the sound when starting. Normal operation is accompanied by a smooth, monotonous hum. If you hear clicks, metallic clanging or knocking, this indicates mechanical destruction of the internal components. Piston group the valve could have worn out, or the valve has broken.
⚠️ Attention: If you hear a loud click when turning on, followed by buzzing, and after a few seconds - another click and silence, the protection system turns off the motor. This may be a sign of an interturn short circuit or jamming of the mechanism.
Also inspect the appearance of the compressor. There should be no traces of oil, severe corrosion or swelling. The presence of oily stains often indicates depressurization of the housing, which makes further operation impossible without replacing the unit. A visual inspection allows you to weed out up to 30% of obvious problems without disassembling the unit.
Checking the starting relay and thermostat
Before sinning on the engine itself, it is necessary to eliminate malfunctions of the control circuit. Often the compressor is absolutely working, but does not receive a signal to start or cannot start due to a burnt-out start relay. This small element is responsible for supplying voltage to the starting winding at the time of start.
To check the relay, it must be removed from the compressor. It is usually mounted on the side of the motor housing and secured with a bracket or screws. Carefully disconnect the wires and remove the device. Visually inspect the contacts: carbon deposits or melting of the plastic indicate overloads. Starting capacitor (if it is in the circuit) also requires checking for swelling.
- 🔌 Checking the contacts: Ring the relay contacts with a multimeter in resistance measurement mode. In normal condition, the circuit should close or open depending on the position (the logic may differ for different types of relays).
- 🌡️ Thermostat: Make sure that the thermostat sends a signal to turn on. Close the thermostat contacts directly (observing safety precautions). If the motor starts, the problem is in the temperature sensor.
- ⚡ Power circuit: Check the integrity of the supply wires. An open circuit between the socket and the compressor will prevent even a serviceable engine from starting.
If after replacing the relay the situation has not changed, and the engine still does not start or the machine knocks out, the problem lies deeper. In modern models with inverter compressors, diagnostics are more difficult, since the start is controlled by an electronic module. In such cases diagnostics requires a special tester.
☑️ Diagnostics before disassembly
Electrical check of the windings with a multimeter
The most accurate way to assess the condition of the electrical part of the engine is to test the stator windings. For this you will need a multimeter. Before starting work, be sure to disconnect the refrigerator from the power supply. Remove the compressor protective casing and get to the contact group.
The contacts usually have three terminals: two working and one common. Remove the start relay to clear the contacts. Set the multimeter to measure resistance (Ohmmeter mode, limit 2 kOhm). Your task is to measure the resistance between each pair of contacts. Normal resistance values depend on the power of the motor, but usually range from 10 to 30 Ohms for the starting winding and slightly less for the working winding.
| Pair of contacts | Normal resistance | Possible malfunction |
|---|---|---|
| Working - General | 10–25 Ohm | Normal / Open |
| Starting - General | 20–40 Ohm | Normal / Open |
| Working - Starting | The sum of the two is higher | Normal / Short circuit |
| Any contact - Housing | Infinity (∞) | Breakdown on housing |
If the device shows infinity (one on the left on the digital display), it means that there is a problem in the winding break. This engine cannot be repaired. If the resistance is close to zero, this indicates a short circuit in the turns. The most dangerous option is a breakdown to the housing when the current passes through the metal casing.
What is an interturn short circuit?
An interturn short circuit is a violation of the insulation between the turns of the winding. The resistance drops, the current increases, the engine gets hot and hums. It is difficult to identify with a multimeter; a test with a current clamp or replacement is required due to overheating.
Assessment of the mechanical part and pressure
Electrical service does not guarantee mechanical integrity. The compressor may sound in all respects, but not create pressure in the system. This occurs when the valves break or the piston group jams. To check the mechanics, they often use the “blow-through” method.
Carefully bite off the capillary tube and the return (suction) tube at the very entrance to the compressor with pliers. Be careful, residual pressure and freon vapor may remain in the system. After disconnecting the tubes, turn on the refrigerator (for a short time!). A powerful stream of air should come from the discharge tube. If it blows weakly or the air flows backwards from the suction tube, the valves are faulty.
⚠️ Attention: Do not keep the compressor turned on without load (with open pipes) for more than 10-15 seconds! This can lead to overheating and damage to the windings, since motor cooling in some models depends on the circulation of freon.
It is also worth checking for the presence of oil. If, during depressurization, a lot of oil leaks from the tubes, this may indicate wear of the oil scraper rings or destruction of the seals. Oil waste reduces the cooling efficiency and clogs the capillary system.
Current consumption and operation under load
The most complete picture is provided by measuring the current consumption. For this you will need current clamps. They allow you to measure current without breaking the circuit, simply by covering one of the power wires of a running compressor. The current value must correspond to the rating data indicated on the housing sticker.
If the current is significantly lower than the nominal value, this indicates that the compressor is running “idle” - without pressure. Most likely, the tightness of the system is broken or the valves are broken. If the current is higher than the rated current, the motor is overloaded. This may be caused by jamming of the mechanism or turn-to-turn short circuit.
It is important to take into account the starting current. At the moment of launch, it briefly increases by 3-5 times. If the start-up is difficult and the current does not drop to operating values for a long time, the protection system will work sooner or later. Long-term operation at high currents leads to destruction of insulation or other failure.
- 📉 Low current: Freon leakage, circuit leakage, valve failure.
- 📈 High current: Stucking, short circuit of turns, high voltage in the network.
- ⚖️ Normal: The current corresponds to the plate on the case (usually 0.5 - 1.5 Amperes for household models).
Symptoms of complete failure
There are a number of signs in which a refrigerator engine test can be considered completed with a negative result. If you observe a combination of electrical breakdown to the frame and mechanical jamming, repair is not economically feasible. The cost of a new compressor and the work to replace it is often 70-80% of the price of a new refrigerator.
A critical symptom is the smell of burnt insulation, accompanied by knocking out plugs throughout the apartment when the unit is turned on. This indicates deep damage to the windings. Also, a sign of the death of the motor is the lack of response to direct start (bypassing the relay) when voltage is applied, when the rotor does not even try to move, but only hums.
The table below shows the main symptoms and probable causes:
| Symptom | Probable reason | Solution |
|---|---|---|
| Buzzing and clicking | Faulty starting relay | Replacing the relay |
| Case is getting hot | Stuck or short circuit | Replacing the compressor |
| Quiet hum, no cold | Break valves | Replacing the compressor |
| Knocks out automatic | Breakdown on the housing | Replacement of the compressor |
Frequently asked questions (FAQ)
Is it possible to start the compressor directly without a relay?
Yes, for a short-term test (for 2-3 seconds) you can apply 220V voltage directly to the working and starting windings. However, this must be done extremely carefully, using a button or a circuit with automatic opening, so as not to burn the starting winding, which is not designed for long-term operation.
Why may a new compressor not start?
The reasons may be incorrect installation of the starting relay (it is important to observe the orientation in the direction of the arrow), low voltage in the network or moisture ingress system, which causes corrosion of the contacts. It is also possible that there is a factory defect.
The sound of a running motor is heard, but the refrigerator does not freeze. What to do?
Most likely, there is a break in the valves inside the compressor or a freon leak. The compressor circulates gas, but does not create the required pressure. You need to call a technician to diagnose the system and, probably, replace the compressor.
Is it dangerous to check the compressor yourself?
Working with 220V electricity is life-threatening. In addition, careless handling of the pipes may result in the release of refrigerant. If you do not have experience, limit yourself to a visual inspection and checking the voltage in the socket.