The situation when the refrigerator compressor hums but does not start often confuses the home handyman. If the diagnostics showed a break in the starting winding or a malfunction of the starting relay, the question arises about the possibility of forcibly starting the engine. Many people try to bypass the standard connection diagram in order to save the unit or pump out freon before disposal. However, it is important to understand that working without a standard starting system is an emergency measure, and not a full-fledged repair.
In this article we will analyze the physical principles of operation of single-phase asynchronous motors used in household appliances. You'll learn why the starting winding is critical to torque production and what happens if you try to start the rotor shaft without it. We will look at the technical nuances of connecting through capacitors and methods of manually turning the shaft, which allow the motor to reach operating mode.
Before you begin any manipulations with the electrical part, you need to make sure that the work being carried out is safe. 220 volt voltage is dangerous to life, and short circuits can damage the wiring. All actions on circuit modifications must be carried out with the power turned off, and test runs must be carried out with extreme caution.
⚠️ Attention: Operation of a refrigeration unit with a modified motor starting circuit is prohibited in domestic conditions. The described methods are suitable only for short-term test runs or emergency restoration of the compressor to pump out refrigerant.
The principle of operation of a single-phase motor and the role of windings
To understand whether it is possible to start a compressor without a starting winding, you need to understand its device. A standard refrigerator motor-compressor has two stator windings: the main (working) and auxiliary (starting) windings. The working winding occupies two-thirds of the stator slots and creates a pulsating magnetic field, which by itself cannot move the rotor.
The starting winding, which has a thinner wire and greater resistance, is shifted relative to the working winding by 90 degrees. It is this that creates the necessary phase shift for the generation of torque. In normal mode, current flows through it only at the moment of start, after which the starting relay opens the circuit. If this winding burns out, the magnetic field becomes symmetrical, and the rotor only hums, remaining motionless.
Technically, it is possible to start the engine without a starting phase, but this requires an external impulse. Torque must be created artificially. Without this, the motor will consume a huge short circuit current, overheat and quickly fail. Therefore, the question is not so much how to start, but how long it will work and what risks it carries.
- 🔌 Working winding - creates the main magnetic field, thick wire, low resistance.
- 🚀 Starting winding - creates a phase shift for start, thin wire, high resistance.
- ⚙️ Rotor - a moving part that begins to rotate only in the presence of a phase shift or mechanical push.
It is important to note that modern inverter compressors are designed differently and They do not have classical starting windings in the usual sense, since the frequency is controlled by electronics. The methods discussed below apply exclusively to classic single-phase asynchronous motors with a starting relay.
Diagnostics of winding integrity before starting
Before attempting to start the unit, it is necessary to accurately determine the nature of the damage. Often, technicians mistakenly believe that the starting winding has burned out, when in fact the problem lies in the starting relay or capacitor. To check, you will need a multimeter switched to resistance measurement mode (Ohms).
First, find the contacts on the compressor. There are usually three of them: general (C), working (R) and starting (S). Call pairs of contacts. The resistance between working and common should be minimal (for example, 10-20 Ohms). The resistance between starting and common will be higher (30-50 Ohms). The sum of these two values should approximately equal the resistance between the working and starting contacts.
⚠️ Attention: If the multimeter shows infinity (open) on the starting winding, it means the wire inside the coil has burned out. Launching without it is possible, but requires the creation of an artificial phase shift. If there is no breakdown in the housing, the motor most likely can be restored or used as a pump.
Also check the resistance between any contact and the copper tube or compressor housing. The device should show infinity. If there is at least some resistance, it means that there has occurred insulation breakdown on the housing, and operating such a compressor is deadly.
Starting method through a capacitor
One of the most effective ways to start a motor with a broken starting winding is to use capacitor. Since the standard starting circuit does not work, we must artificially create a phase shift. To do this, the capacitor is connected in series with the working winding or in parallel, simulating the operation of the starting system, but with different parameters.
The connection diagram requires precise selection of capacitance. If the capacity is too small, the engine will not be able to develop enough torque and will hum. If it is too large, the windings will begin to overheat. Typically, for compressors with a power of 100-200 W, capacitors with a capacity of 20 to 50 μF with an operating voltage of at least 300-400 Volts are used.
The connection is made as follows: one terminal of the capacitor is connected to the working contact of the compressor, and the second to the network. However, when the starting winding is burned out, a circuit is often used where the capacitor helps the working winding to operate in a mode close to three-phase.
Calculation of capacitance
To select the capacitance, there is an empirical formula: 7 μF for every 100 W of engine power. However, for refrigerator compressors this value may vary, and it is better to start with a lower value and gradually increase the capacitance while monitoring the case temperature.
When using this method The capacitor must be designed to work with alternating current (AC), conventional DC electrolytic capacitors may explode. This is a critical safety point.
Mechanical starting and use of a start relay
There is a simpler, but risky method that is often used by craftsmen when pumping out freon. Its essence is to apply voltage only to the working winding and manually give the rotor shaft a rotational movement. As soon as the rotor begins to rotate, the engine will enter operating mode and work independently.
To implement this method, the compressor is connected to the network through a working starting relay, but the starting winding circuit is ignored (since it has burned out). At the moment of power supply, it is necessary to sharply rotate the motor shaft. Since the shaft is hidden inside the housing, this cannot be done without disassembling, so the method is applicable only if you have access to the shaft (for example, the compressor is being converted into an airbrush compressor).
If the compressor is sealed, mechanical starting from the outside is impossible. In this case, the method of “spin up” with current is sometimes used, applying short-term pulses of increased voltage, but this requires complex equipment. A more realistic option for sealed blocks is to use an external starting capacitor large capacitance, which is connected for a split second in parallel to the working winding at the moment of start.
- 🛠️ Prepare a capacitor of suitable capacity and voltage.
- 🔌 Assemble the connection diagram, excluding the burnt winding.
- ⚡ Apply power and control the temperature of the case in the first minutes.
- 👂 Listen to the sound of operation: a smooth hum is normal, a crackling sound is dangerous.
☑️ Check before starting
Comparison of launch methods and their effectiveness
The choice of method depends on your goals and available equipment. If you just need to check if the compressor mechanical unit is alive, the capacitor method will do. If you plan to use the unit further, it is worth assessing the economic feasibility. Rewinding an engine often costs more than a new compressor.
The table below compares the main methods of resuscitating a motor with a faulty starting system:
| Method | Difficulty | Risk of breakdown | Durability |
|---|---|---|---|
| Start via capacitor | Medium | High (overheating) | Low |
| Mechanical promotion | High | Medium | Medium |
| Rewinding | Very high | Low | High |
| Replacement of the compressor | Medium | Low | High |
As can be seen from the table, the most reasonable solution for a household refrigerator is replacing the compressor. The “treatment” methods are temporary and can lead to a wiring fire or final jamming of the piston group.
Safety precautions and possible risks
Working with electric motors under 220V voltage always carries risks. When experimenting with windings, there is a high probability of a short circuit. If you use capacitors, they may retain a charge even after being unplugged, so always discharge them before touching the contacts.
Overheating is another serious risk. An engine running without a standard starting winding or with an incorrectly selected capacitor will heat up more than usual. The thermal relay may not operate in time, which will lead to melting of the insulation and a fire. Casing temperature should not exceed 90 degrees Celsius.
⚠️ Attention: It is strictly forbidden to leave a compressor operating in experimental mode unattended. In case of jamming of the piston group or fire of the windings, you must immediately de-energize the installation.
Also remember about the refrigerant. If you open the system to replace the compressor, freon comes out. In confined spaces this can lead to suffocation, and upon contact with an open flame, freon decomposes and releases phosgene, a chemical warfare agent.
FAQ: Frequently Asked Questions
Is it possible to permanently leave the refrigerator operating with a capacitor instead of a starting winding?
Theoretically, this is possible, but not recommended. This operating mode causes increased heating and reduces engine life. This is acceptable as a temporary solution for a few days, but not for permanent operation.
Which capacitor to choose to start a 1/5 hp compressor?
For a compressor with a power of about 150-200 W (approximately 1/5 - 1/4 hp), starting capacitors with a capacity of 30-50 are usually used µF with a voltage of at least 330V. It is better to select the exact value experimentally, starting with a smaller one.
Why does the compressor hum, but does not start without a starting one?
Humming means that current is supplied to the working winding and a magnetic field is created, but it is not rotating, but pulsating. Without the phase shift provided by the starting winding or capacitor, the rotor cannot overcome inertia and friction.
Is it dangerous to touch the housing of a running compressor with such a circuit?
If the insulation is broken or there is a breakdown, the housing may be energized. Always check the body for potential absence with an indicator screwdriver and use grounding. Working with an ungrounded metal case is deadly.