The situation when the refrigerator stops cooling and the compressor is silent or makes only a quiet hum, and often takes you by surprise. In most cases, the culprit is starting relay, which stops providing an impulse to start the engine. Many repairmen immediately offer to replace the unit, but for accurate diagnostics or emergency starting (for example, to pump out freon or check the tightness of the system), you need to know how to start the engine directly. This requires not only theoretical knowledge, but also strict adherence to safety precautions.
Before proceeding with any manipulations with the electrical part, you should understand that single-phase asynchronous motorinstalled in household refrigerators is not able to start on its own. It needs a phase shift, which is precisely what the starting winding provides through the relay. Ignoring this principle will only lead to humming and overheating of the windings without rotation of the shaft. In this article we will analyze the physical basis of the process, diagnostic methods and the forced start algorithm itself.
It is important to immediately note that this method is a temporary solution for diagnostics or emergency pumping out of refrigerant. Continuous operation of the compressor without standard thermal protection and a starting relay is strictly prohibitedas this can lead to overheating of the windings and fire. Next, we will consider in detail the design of the motor and the step-by-step algorithm of actions.
The operating principle of a single-phase refrigerator motor
The heart of the refrigeration unit is an electric motor operating from an alternating current network. Unlike three-phase analogues, a single-phase motor has two windings on the stator: the main (working) and auxiliary (starting) windings. The working winding creates a magnetic field, but it is not enough to initially move the rotor from its place. That is why a short-term connection of the starting winding is required, which creates the necessary torque.
In normal mode, this process is controlled starting relay. It supplies current to the starting winding at the moment of switching on and turns it off when the engine reaches about 75% of the rated speed. If you try to apply voltage only to the working winding, the rotor will remain motionless and the engine will emit a characteristic hum. The current in this case will increase several times, which will quickly lead to overheating and internal protection tripping or insulation burnout.
To manually start, we need to artificially simulate the operation of the relay. This means that we must apply voltage to both windings at the moment of start, and then, after a short time (usually 1-3 seconds), break the circuit of the starting winding, leaving power only on the working one. The difficulty lies in precise timing: if you remove the starter too early, the motor will not start; if you wait too long, the winding will burn out.
⚠️ Attention: All work on connecting the compressor is carried out under a voltage of 220 Volts. Do not touch live parts with your hands while the engine is running. Use tools with dielectric handles and a rubber mat.
There are several ways to implement this task: from using a button with normally open contacts to assembling a simple circuit with a capacitor. The choice of method depends on the availability of tools and experience with electrical work. In any case, the primary task remains identifying the winding terminals.
Identification of contacts and checking the windings
Before assembling the starting circuit, it is necessary to determine exactly which pin on the compressor terminal block corresponds to the working, starting winding and common wire. Typically the contacts are arranged in a triangle, but their markings may be erased or missing. For diagnostics, you will need a multimeter switched to resistance measurement mode (Ohm).
The dialing process begins with a visual inspection and cleaning of the contacts. Then the resistance between each pair of terminals is measured. The sum of the resistances of the two smaller values should be equal to the largest value (resistance between the extreme terminals). This is the basic law of physics for such engines, allowing you to identify the purpose of the contacts without documentation.
Let's consider typical resistance values for different types of compressors. They may vary depending on the power and manufacturer, but the proportions remain similar. The working winding always has less resistance, since it is wound with a thicker wire, and the starting winding has a larger one.
| Pair of contacts | Expected resistance | Pin assignment |
|---|---|---|
| Common - Working | 10-25 Ohm (lower value) | Main winding |
| Common - Starting | 20-50 Ohm (higher value) | Starting winding |
| Worker - Starter | Sum of the previous two | Total resistance |
| Any - Housing | Infinity (∞) | Check for breakdown |
If the multimeter shows a resistance close to zero between the winding and the housing, then it has occurred insulation breakdown. Operating such a compressor is life-threatening. Also an alarming signal is the absence of resistance (break) on one of the windings. In both cases, starting the motor is impossible without major repairs or replacement of the unit.
Necessary tools and materials
To successfully carry out the starting procedure, you will need a minimum set of tools that most home craftsmen will have. However, the quality of execution directly affects the safety of the process. You should not use damaged wires or electrical tape with a broken adhesive layer.
The main tool is multimeter, without which primary diagnosis is impossible. You will also need a set of screwdrivers for dismantling the casing and removing the terminals, pliers with insulated handles, and possibly a wire stripper. For the connection itself, it is best to use a copper wire with a cross-section of at least 0.75 mm².
☑️ Ready to start
As a switching element, you can use a regular doorbell button (with normally open contacts) or a special starting capacitor, if required softer start. It is important that the button can withstand a current of at least 10 Amps, since the starting currents of the compressor can reach high values.
Do not forget to prepare personal protective equipment. Rubber gloves and goggles will protect you from accidental sparks or oil splashes if there is a leak in the system. Also have a fire extinguisher on hand, although the likelihood of a fire during a short-term test is minimal, fire safety measures cannot be neglected.
Connection diagram and action algorithm
Once the contacts have been identified, you can begin assembling the temporary circuit. The essence of the method is to apply voltage to the common and working terminals constantly, and to the starting terminal - briefly, at the moment of switching on. To do this, it is convenient to use a button with two pairs of contacts or one button in a break in the starting circuit.
The algorithm of actions is as follows. First, connect one wire from the plug to the compressor common terminal. Connect the second wire from the plug to the working terminal. Connect the third wire (from the same phase as the second) to the start terminal through the button. Thus, when the button is pressed, the circuit closes and the engine receives an impulse to start.
What to do if the compressor hums, but does not start?
If when you press the button, the motor hums, but the shaft does not rotate, the piston mechanism may be jammed or there is not enough voltage in the network. An interturn short circuit may also be the cause. Do not hold the button pressed for more than 3-5 seconds - the winding will burn out. Try turning the shaft slightly (if you have access) or tapping the compressor body with a wooden handle. If it doesn’t help, the motor is mechanically faulty.
When the plug is plugged into the socket (or power is supplied), you must immediately press and hold the button on the starting circuit. As soon as the engine starts (usually this is accompanied by a change in the humming sound to a smooth hum of operation), the button must be released. If everything is done correctly, the motor will continue to operate on the working winding.
⚠️ Attention: The time of pressing the button should not exceed 2-3 seconds. If the compressor does not start during this time, turn off the power and look for the reason. Holding the starting winding energized for a long time is guaranteed to lead to its combustion.
For more advanced users, there is a circuit using Starting capacitor. It is connected in parallel with the starting winding and allows you to create a more powerful shear pulse, which makes it easier to start the engine under load. However, for simple diagnostics, the push-button method is sufficient.
Diagnosis of faults during startup
Even with correct connection, the compressor may behave unexpectedly. Understanding the nature of engine sounds and reactions helps make an accurate diagnosis. For example, if the motor hums but does not turn, this may indicate a mechanical wedge or electrical problems.
A common problem is turn-to-turn short circuit in the windings. In this case, the resistance of the windings will be below normal, and when you try to start, the circuit breaker in the panel will be knocked out or the fuses will burn out. You can check this not only with an ohmmeter, but also with a current clamp: the current consumed will significantly exceed the rated values.
Another common situation is the operation of an internal thermal relay. If the compressor was overheated by previous starting attempts, the bimetallic strip inside could break the circuit. In this case, the motor will be silent. You need to let it cool for 30-40 minutes before trying again.
If the engine starts, but runs with strong noise and vibration, this indicates mechanical wear of the components or damage to the shock absorbers. Operation of such a unit is possible only for short-term purposes (for example, pumping out freon), but not for long-term work in a refrigerator.
Safety measures and common errors
Working with high voltage and sealed systems requires maximum concentration. A typical mistake for beginners is neglecting to insulate the places where the wires are twisted. Use high-quality terminal blocks or carefully insulate the connections with PVC tape to avoid short circuits.
Never leave a compressor running without a relay unattended. The standard relay often performs the function of overheating protection, turning off the motor at critical temperatures. In our scheme, this protection is absent, so control of the temperature of the case (especially in the area of the lower part where the tubes come out) must be constant.
It is also important to remember about the refrigerant. If you run the motor to pump out freon, make sure the room is well ventilated. Some types of refrigerants are heavier than air and can displace oxygen, and when in contact with an open flame, form toxic compounds.
Using wires that are too thin for connection is also considered a mistake. The starting current can be 5-7 times higher than the working current, and the thin conductor will simply burn out, causing a short circuit. Use wires with a spare cross-section.
Frequently asked questions (FAQ)
Is it possible to leave the refrigerator to work forever without a relay?
Theoretically, you can assemble a circuit with a capacitor and a button, but this is extremely inconvenient and unsafe. You will have to manually turn on the motor every time the thermostat calls for cold. In addition, without thermal protection, there is a high risk of burning the compressor during power surges or jamming.
Why does the compressor hum, but does not start even with a button?
There may be several reasons: jamming of the piston group (mechanical failure), interturn short circuit in the windings, insufficient voltage in the network or capacitor malfunction (if it is used). Also check whether you have correctly identified the winding terminals.
What resistance should be between the terminals of a working compressor?
The exact numbers depend on the model, but usually the resistance of the working winding is 10-25 Ohms, and the starting winding is 20-50 Ohms. The resistance between any terminal and the body must be infinite. If the resistance of the windings is significantly lower than normal (for example, 1-2 Ohms), an interturn short circuit is likely.
Is it possible to use a car battery for starting?
No, the compressors of household refrigerators operate on 220V alternating current. A car battery will produce a constant current of 12V, which not only will not start the engine, but can also damage the windings. To start from a battery, an inverter is required, which makes the circuit cumbersome and impractical.