How to connect an old refrigerator without a relay: a master's guide

In a situation where a household refrigerator suddenly stops cooling, and diagnostics indicate a faulty start relay, the question of temporary starting often arises unit. This may be required to pump out freon, check the tightness of the system, or assess the condition of the freon itself compressor before its disposal or replacement. Understanding the principle of operation of the electric motor allows you to perform this procedure, however, it requires strict adherence to safety precautions and basic knowledge in electrical engineering.

The lack of a standard relay means that you will have to manually imitate its operation or use alternative starting methods single-phase motor. It is important to realize that this method is purely diagnostic or emergency. Operating refrigeration equipment in this mode for a long time is strictly not recommended, as this can lead to overheating of the windings and other failure of an expensive unit.

Before proceeding with any manipulations with the electrical part, it is necessary to completely de-energize the device. Working with high voltage poses a direct threat to life, so use only working tools and dielectric gloves. Next, we will analyze in detail the design of the motor, methods for determining serviceable windings and methods for switching them to start.

Design and principle of operation of the compressor

The heart of any refrigeration unit is a hermetic compressor, inside of which the electric motor is located. Most older models are used asynchronous motors with a squirrel-cage rotor. To start them, the creation of a rotating magnetic field is required, which is achieved due to the presence of two different stator windings: starting and working. It is the correct interaction of these elements that ensures the rotation of the shaft.

Starting winding has a thinner wire and a larger number of turns, which creates a high active resistance. It is connected to the network only at the time of startup in order to create the necessary initial rotation impulse. Working winding it is made with a thicker wire and is designed to maintain rotor rotation in normal operation. The separation of these functions is the main task of the starting relay, which we exclude from the circuit.

In the standard circuit, a time or current relay automatically turns off the starting winding a fraction of a second after the start of rotation. When connecting manually, this function must be taken over by the operator or special capacitor circuits must be used. Understanding the physics of the process helps to avoid mistakes that can lead to the motor humming without rotation or insulation burnout.

⚠️ Attention: The sealed compressor housing heats up to high temperatures during operation. Do not touch the metal parts of the unit during test runs without protective gloves to avoid thermal burns.

Why can’t you keep the starting winding on for a long time?

If you leave the starting winding in the circuit after the rotor accelerates, too much flow will flow through it current This will lead to rapid overheating of the thin wire, melting of the insulation and an inter-turn short circuit, which will completely disable the motor.

Necessary tools and safety measures

To carry out work on direct connection of the motor, you will need a minimum set of tools that most home craftsmen can find. It is critical to prepare everything in advance so that you are not distracted when voltage is applied. The main tools will be a multimeter for testing circuits, a set of screwdrivers, pliers and insulating materials.

Particular attention should be paid to measuring instruments. Multimeter must be in working order, and its probes must have complete insulation. You will need a resistance (ohms) measurement mode to identify the windings. It would also be a good idea to have a current clamp if you plan to monitor the inrush current, although for a one-time procedure, visual control and hearing are sufficient.

Safety is priority number one. All connections must be made reliably, using high-quality insulation. Use terminal strips or high-quality electrical tape to prevent accidental contact with live parts. Work with only one hand, keeping the other in your pocket to reduce the risk of current passing through the heart in the event of a shock.

Identification of contacts and continuity of windings

The first stage will be the determination winding terminals on the compressor housing. They are usually located at the bottom of the unit and covered with a plastic cover. Once you remove the cover and disconnect the old relay, you will see three contacts forming a triangle. The task is to understand which terminal belongs to which winding.

Using multimetermeasure the resistance between each pair of contacts. You need to find the pair with the least resistance - these will be the ends of the working winding. A pair with high resistance will indicate a series connection of the working and starting windings. The remaining contact will be common.

For clarity, you can use the following table, which will help interpret the readings of the device:

If the device shows a resistance close to zero or, conversely, infinity between the terminals of the windings, this indicates a motor malfunction. In the first case there is a short circuit, in the second there is a break. In such cases, connecting without a relay is impossible and makes no sense.

Direct motor connection diagrams

There are several ways to start a motor without a standard relay. The simplest method involves briefly applying voltage to the starting winding manually. To do this you will need a piece of wire with a plug. One end is connected to the common terminal and the working terminal, and the second end briefly touches the starting terminal.

A safer and more convenient option is to use a button with normally open contacts. The button is connected to the break in the starting winding circuit. The circuit looks like this: the phase goes to the working terminal constantly, and to the starting terminal - through the button. By pressing the button, you give a pulse, the motor starts, and the button can be released.

The third option, which is often used for powerful compressors, involves using capacitor. The capacitance is selected experimentally, usually in the range of 20-50 µF with a voltage of at least 300V. The capacitor is connected in series with the starting winding, which creates the necessary phase shift for a reliable start.

Circuit with a button:
Phase (L) --> [Working contact]
Phase (L) --> [Button] --> [Start contact]
Zero (N) --> [General contact]

It is important not to overpress the power button. 1-2 seconds are enough for the rotor to gain momentum. Holding it for a long time will lead to overheating of the starting winding. If the motor does not start on the first try, pause to cool before retesting.

Diagnostics of startup problems

Even with correct switching, difficulties may arise. If a hum is heard when voltage is applied, but the shaft does not rotate, this may indicate that the mechanical part of the compressor is jammed. In older models, oil loss or acid deposits often form, which blocks the piston group.

Sometimes the problem lies in insufficient voltage in the network or poor contact at the junction of the wires. Check the reliability of the twists and the condition of the insulation. It is also worth making sure that the starting winding is actually receiving current. To do this, you can use indicator screwdriver or re-check the multim circuit.

If the motor starts, but the circuit breaker immediately knocks out or the fuse blows, it means that a short circuit has occurred in the windings. This unit cannot be used. Also an alarming signal is the appearance of smoke or a burning smell from under the casing.

⚠️ Attention: If the compressor hums but does not start for more than 3 seconds, immediately turn off the power. Prolonged humming with a blocked rotor burns the winding in a matter of minutes.

Assessing the condition of the oil and tightness

When starting an old refrigerator for diagnostics, it is important to evaluate the quality of the oil. If you plan to pump out freon, do it through a puncture in the process pipeline. The color of the oil coming out will tell a lot: clear or light yellow oil indicates the normal state of the system.

Dark, almost black oil with a burning smell indicates overheating of the compressor and decomposition of the lubricant. In this case, even a new compressor installed in such a system will not last long. A complete flushing of the circuit with nitrogen is required, which is only possible in a workshop.

Also pay attention to the presence of metal shavings in the oil. This is a sign of severe mechanical wear of rubbing parts. The presence of moisture in the system (emulsion instead of oil) indicates a violation of the seal and the entry of air, which leads to corrosion of internal parts.

Is it possible to leave the refrigerator working without a relay all the time?

Theoretically, you can assemble a circuit with a capacitor that will work constantly, but this is extremely ineffective. The standard relay ensures optimal operation. Constant operation of the starting winding or the use of an unsuitable capacitor will lead to a decrease in efficiency, overheating and eventual breakdown.

How to determine whether the compressor or just the relay has burned out?

Test the windings with a multimeter. If the resistance between the terminals tends to zero (short circuit) or infinity (break), or if there is a breakdown to the housing, the compressor is faulty. If the resistance is normal, but the motor does not start even when directly connected to a capacitor, mechanical jamming is possible.

Which capacitor is best to use for starting?

For single-phase refrigerator motors, special starting capacitors (CD type) are used. They are designed for short-term operation at high voltage. It is dangerous to use conventional electrolytic capacitors - they can explode.

Why does the compressor heat up when operating without a relay?

If the connection diagram is incorrect (for example, both windings operate constantly), the current in the motor exceeds the rated one. Also, the reason may be low voltage in the network or a lack of refrigerant, due to which the motor does not receive proper cooling by the freon flow.

Is it dangerous to open the sealed casing yourself?

Yes, it is dangerous and impractical. Inside there is compressed gas and oil. In addition, factory welding provides a seal that cannot be replicated at home. Repairing the “inside” of the compressor requires industrial equipment.