In a situation where a household refrigerator fails and the start relay burns out at the most inopportune moment, the owner is often faced with the question of the possibility of temporarily starting the unit. This may be required to pump out freon, check the tightness of the system, or emergency cooling of products before purchasing spare parts. Direct connection of the compressor to the electrical network is a technically feasible procedure accessible to a person with basic electrical installation skills, but it requires strict adherence to safety precautions and an understanding of the principles of operation of the electric motor.
Modern and old models of refrigerators, be it Atlant, Indesit or Stinol, use asynchronous motors that cannot start on their own without creating a rotating magnetic field. In normal mode, this function is performed by a starting relay, but in its absence, the task must be solved manually or using a temporary circuit. The main difference between direct starting and standard starting is the absence of automatic shutdown of the starting winding, which requires constant monitoring of the process.
Before starting work, you must clearly understand the risks: lack of protective automation can lead to overheating of the windings and even fire if the current and operating time are not controlled. This instruction describes a method that should be considered solely as a temporary measure for diagnostics or emergency situations, and not as a method of permanent operation of the equipment.
The principle of operation and design of a single-phase motor
The electric motor installed in compressor unitis asynchronous and has two main windings: working and starting. The working winding occupies most of the stator slots and provides the main rotation of the rotor, while the starting winding is necessary only to create the initial torque. Without the participation of the starting winding, the rotor will remain motionless, only emitting a characteristic hum.
In the standard circuit, the relay opens the starting winding circuit immediately after the engine reaches about 75% of the rated rotation speed. With a direct connection, this function is taken over by the operator or a temporary control device. It is important to understand that if you leave the starting winding connected to the network for a long time, it will burn out due to high resistance and lack of design ability to withstand long-term load.
For successful starting, it is necessary to correctly determine the winding terminals on the motor terminal block. Usually there are three of them: one common, one for the working winding and one for the starting winding. Resistance between the common wire and the working winding is always less than between the common and starting winding. This is a key point that allows you to identify contacts without technical documentation.
⚠️ Attention: Never leave a running compressor unattended when connected directly. The absence of a standard thermal relay can lead to critical overheating of the case and melting of the insulation in a matter of minutes.
Necessary tools and preparation of the workplace
To carry out the work, you will need a minimum set of tools that most home craftsmen can find. First of all, you need a multimeter to test the windings and determine their integrity. You will also need pliers, insulating tape, screwdrivers and possibly wire cutters to prepare the wires.
Particular attention should be paid to the power source. The connection must be made to a working socket with grounding, capable of withstanding starting currents, which can be 5-7 times higher than the rated current of the motor. Use of cheap extension cords or twisting in the power circuit is strictly not recommended, as they can cause a voltage drop and unsuccessful starting.
Prepare a place to place the compressor. The unit must be placed on a flat, non-conductive surface. Since oil splashes or sparks may occur when working without the standard cover, make sure that there are no flammable objects around. It is also recommended to have a fire extinguisher on hand.
- 🔧 Multimeter with resistance measurement mode (Ohm) for diagnosing windings.
- 🔌 Cable with a plug and core cross-section of at least 1.5 mm² for safe connection.
- 🧤 Dielectric gloves for protection against damage electric shock.
- 🧰 Screwdrivers and tools for removing the compressor protective casing.
☑️ Preparation for startup
Identification of contacts and continuity of windings
The most important step is to determine the purpose of the three contacts on the compressor terminal block. They are usually arranged in a triangle. On some models, such as Donbass or Biryusa, the markings may be erased or missing, so you will have to rely only on measurements.
Take a multimeter and switch it to resistance measurement mode (limit 2 kOhm). Call all pairs of contacts with each other. You will get three resistance values. The sum of the two smaller resistances should be approximately equal to the largest resistance (between the extreme contacts). The greatest resistance is the sum of the resistances of the working and starting windings.
The contact, relative to which the other two show the least resistance, is common wire. Between the common wire and the contact with lower resistance there is a working winding. Between the common wire and the contact with the larger (of the remaining two) resistance is the starting winding. It is to the starting winding that you will need to briefly apply voltage to start.
| Pair of contacts | Resistance value (approximate) | Winding type |
|---|---|---|
| Common - Working | 10-25 Ohm (lower value) | Working winding |
| Common - Starting | 30-50 Ohm (average value) | Starting winding |
| Working - Starting | Sum of the previous two (largest) | Full circuit |
⚠️ Attention: If the multimeter shows infinity (open) or zero (short circuit) on any of windings, it is prohibited to start the compressor. This indicates an internal malfunction of the engine, and connecting to a 220 volt network will lead to knocked out plugs or a fire.
What to do if the resistances are the same?
In rare cases, especially on old Soviet motors, the resistances of the windings can be very close. In this case, try to determine the windings by the thickness of the wire inside the coil (if visible) or by the exclusion method, connecting the supposed starting one via a button.
Schemes for direct connection to a 220 volt network
There are several ways to start an engine without a standard relay. The simplest and safest for short-term tests is to use a button with normally open contacts. One wire from the network goes to the general contact of the compressor, the second to the working contact. The starting contact is connected to the working contact through a button, which must be pressed at the moment of switching on and released after the engine starts.
A more advanced option involves the use of a capacitor. Starting capacitor it is connected in series with the starting winding. The capacitor capacity is selected experimentally, but usually ranges from 2 to 4 µF for every 100 W of motor power. This creates the phase shift necessary for a confident start and reduces the risk of overheating.
To implement the circuit, you will need to assemble a circuit where the phase wire of the network is broken by a button or switch that controls the starting winding. It is important not to mix up the wires: if you apply 220 volts directly to the starting winding without a working winding, the engine will burn out instantly. The working winding must be connected to the network constantly for the entire duration of operation.
- ⚡ Connect one mains wire to the common contact of the compressor.
- ⚡ Connect the second mains wire to the working contact (via a circuit breaker).
- ⚡ Third wire (from a button or capacitor) connect to the starting contact.
- ⚡ When starting, briefly close the starting winding circuit.
Starting process and monitoring the operation of the unit
After assembling the circuit, you can begin a test run. Plug the plug into the outlet. At this moment the engine should be at rest. Press the start button sharply (or briefly connect the contacts of the starting winding). You should hear a confident hum and feel vibration.
As soon as the engine picks up speed (usually this takes 1-3 seconds), the starting winding circuit must be broken. If you are using a capacitor circuit without a button, the capacitor must be rated for short-term operation or must be manually turned off. Long-term operation on the starting winding is unacceptable.
Control the body temperature. In normal mode, the compressor heats up, but should not burn your hands. If after 5-10 minutes of operation the case temperature exceeds 60-70 degrees, or a cracking sound is heard, the hum becomes intermittent - immediately turn off the power. These are signs of an interturn short circuit or a wedge in the mechanical part.
⚠️ Attention: Technical characteristics of compressors may vary depending on the manufacturer and year of manufacture. Always check the nameplate on the device case: the voltage must strictly correspond to 220-230V, and the frequency - 50Hz.
Typical errors and safety measures
One of the most common mistakes is ignoring phasing. Although the direction of rotation is not critical for an AC induction motor (in a compressor it is fixed by the design of the valves), incorrect connection can lead to operation without pressurization. They also often forget about grounding the case, which is fatal if the insulation breaks down.
Another mistake is using wires that are too thin. The inrush current is high, and a thin wire can simply melt, causing a short circuit. Use copper wire with a cross-section of at least 1.5 mm², and preferably 2.5 mm². All connections must be reliably insulated with heat shrink or high-quality electrical tape.
Do not try to start the compressor if oil is coming out of the tubes or signs of freon leakage are visible. Working in a vacuum or with a broken seal will quickly damage the motor, since freon normally participates in cooling the motor windings. Tightness systems are a prerequisite for long-term operation.
- 🔥 Do not leave the running unit on a carpet or wooden floor without a fire-resistant substrate.
- 🔌 Always use an RCD or differential circuit breaker in the power circuit.
- 👀 Watch the color of the air leaving the compressor (if you check the discharge) - oil should not fly in a stream.
Frequently asked questions (FAQ)
Is it possible to leave the compressor running without a relay all the time?
No, this is extremely dangerous. The standard relay not only starts the engine, but also protects it from overloads. Without it, the motor may burn out due to a power surge or jamming of the piston group. Use this method only for short-term tests.
What capacitor is needed to start the compressor?
Single-phase refrigerator motors usually require starting capacitors with a voltage of at least 300V (preferably 450V) and a capacity of 2 to 5 µF. The exact value depends on the power of a particular motor and is selected experimentally based on the cleanliness of the start.
Why does the compressor hum, but does not start?
Most likely, the starting winding does not work, the capacitor (if used) is faulty, or the mechanical part of the compressor is jammed. Also, the reason may be low voltage in the network, which does not allow developing sufficient torque.
Is it dangerous to touch copper tubes during work?
Yes. During operation, the compressor heats up, and at the discharge outlet the temperature of the tubes can reach 80-90 degrees and higher. In addition, if the seal is broken, hot oil may escape. Carry out all manipulations only after turning off the power and cooling the unit.