Restoration the functionality of an old refrigerator or creating a homemade compressor for painting work often requires connecting the motor to the mains yourself. Many craftsmen are afraid to take on this task, believing that it is impossible to cope without deep knowledge of electrical engineering. However, understanding the principle of operation single-phase asynchronous motor and having a basic set of tools, it is quite possible to make the connection in a home workshop.
The main difficulty is that the windings of a refrigerator motor cannot operate directly from alternating current without auxiliary elements. Unlike industrial three-phase units, household models require the creation of a rotating magnetic field artificially. It is for this purpose that there are starting devices in the circuit, which for a short time connect an additional winding, shifting the phase and giving the rotor an initial impulse.
Before proceeding with installation, it is necessary to strictly follow safety rules when working with high voltage. Any error when switching wires can lead not only to the failure of expensive equipment, but also to electrical shock electric shock In this article we will analyze in detail the connection diagram, the selection of necessary components and the nuances of setting up the starting relay for various types of compressors.
⚠️ Attention: All work on connecting the compressor to a 220V network should only be carried out with the power completely turned off. Make sure that the plug is removed from the socket and the capacitors are discharged before touching any contacts.
The design and principle of operation of the compressor motor
The heart of any refrigeration unit is a sealed unit, inside which the electric motor and the compressor itself are located, immersed in an oil environment. The motor, as a rule, is asynchronous and has two main windings wound on the stator. The first winding is called the working or main winding, it occupies two-thirds of the stator slots and is designed to create the main magnetic flux.
The second winding, called the starting winding, occupies the remaining part of the slots and is made of thinner wire. Its task is to create an additional magnetic flux, shifted in phase relative to the working winding, which is necessary for the generation of torque at the time of start-up. Without this phase shift, the motor rotor would remain motionless, only humming from the passing current.
The windings are separated and switched using a special device - a starting relay. Older models used relays with a posistor, which closed the starting winding circuit only while the engine was accelerating. In more modern and powerful units, electromagnetic relays are used, where the current in the working winding controls the opening of the starting circuit contacts. Understanding this logic is critical for proper connection.
How to distinguish the working winding from the starting winding?
The working winding always has a larger wire cross-section and, therefore, lower resistance (usually 10-20 Ohms). The starting winding is wound with a thinner wire, so its resistance is higher (often 30-50 Ohms or more).
Necessary tools and materials for connection
To successfully complete the work of connecting the compressor, you will need to prepare a certain set of tools and components. Missing even one key element can make the process impossible or unsafe. The main tool will be a multimeter, which will allow you to ring the windings and determine their integrity before applying voltage.
You will also need screwdrivers, pliers, insulating tape or heat-shrinkable tubing to protect the connections. If you plan to use the compressor for external purposes (for example, as a pump), do not forget about hoses and fittings, but they are not required for the initial electrical connection. Pay special attention to the quality of the wires used - they must withstand starting currents, which can be several times higher than the rated ones.
- 🔧 Multimeter or tester for measuring winding resistance.
- 🔌 Starting relay corresponding to the model of your compressor (the markings must match).
- ⚡ Capacitor (if required for your engine type) with an operating voltage of at least 450V.
- 🧵 Copper wires with a cross-section of at least 1.5 mm² for connecting to the network.
- 🛡️ Circuit breaker or fuse to protect the circuit.
Separately, it is worth mentioning the starting relay. This device is a consumable item and is often the first to fail. When purchasing a new relay, be sure to check the markings on the body with the old part or the technical data sheet of the compressor. Not universal these components are a common cause of unsuccessful startup attempts.
Connection diagram: step-by-step instructions
The connection process begins with pin identification windings on the compressor housing. There are usually three of them: general, starting and working. If the markings are erased or missing, you can determine the purpose of the contacts using a multimeter in resistance measurement mode. Find a pair of contacts with the least resistance - this will be the sum of the resistances of the working and starting windings, and the third, remaining contact is common.
After determining the common wire (Common), you need to find the working and starting windings. The resistance between the common wire and the working terminal will be less than between the common and the starting terminal. It is to these terminals that the starting relay is connected. The connection diagram is standard: the phase goes to the common wire, and the zero branches through the relay to the working and starting windings.
☑️ Check before the first start
It is important to correctly orient the starting relay on the compressor. On its body there is often an arrow or the inscription “Top” indicating the top position. Incorrect installation of the relay may result in the contacts not closing or not opening at the right time, which will cause the motor to hum and overheat the windings. After installing the relay, connect the wires according to the color markings or diagram on the relay body.
| Parameter | Working winding | Start winding | Common wire |
|---|---|---|---|
| Resistance | Low (10-25 Ohm) | High (20-60 Ohm) | Total |
| Wire thickness | Thick | Thin | Medium |
| Operating time | Constantly | Only at start-up | Constantly |
| Wire color (often) | Red/White | Blue/Black | Yellow/Green |
The role of the starting relay and capacitor
The starting relay is a circuit breaker that controls the starting winding circuit. When the compressor is turned on, the rotor is motionless, and the current in the working winding is maximum. This creates a magnetic field that draws in the electromagnetic relay core, closing the contacts of the starting winding. The engine begins to accelerate.
When the speed reaches approximately 75% of the nominal speed, the current in the working winding drops, the magnetic field weakens, and the spring opens the contacts of the starting circuit. The motor continues to operate only on the working winding. If the relay is stuck closed, the starting winding will burn out due to overheating, since it is not designed for long-term operation.
⚠️ Attention: In some circuits, especially for high-power compressors or when operating in low voltage conditions, a capacitor may be connected in parallel with the starting winding. Its capacity and voltage must strictly comply with the requirements of the motor manufacturer.
The capacitor serves to increase the starting torque, creating a stronger phase shift. However, most household refrigerators use split-phase motors, where a capacitor is not required and the phase shift is provided by the different active and inductive resistance of the windings. Installing a capacitor of the wrong capacity can lead to the opposite effect - the engine will heat up and hum.
Diagnosis of faults during startup
Even with correct connection, problems may arise with starting the unit. The most common symptom is a characteristic beep that lasts a few seconds, after which the thermal protection is triggered and a click is heard. This indicates that the engine is trying to start, but it does not have enough starting torque or the piston block is mechanically jammed.
If the compressor is silent and does not make any sounds, check the integrity of the windings with a multimeter. An open circuit will mean that current simply does not flow to the motor. It is also worth checking the thermal protection relay, which may be open due to previous overheating. It needs to be given time to cool down or replaced if it is faulty.
If the engine starts but quickly turns off due to overload, the tightness of the system may be broken or there are problems with pressure. However, if you connect the motor separately from the refrigeration system (without freon and pressure), such a reaction may indicate an interturn short circuit in the windings.
- 🔊 Humming and clicking - the start relay is faulty or the compressor is jammed.
- 🔇 Complete silence - open circuit, burnt out winding or a fault in the wiring.
- 🔥 Burning smell or smoke - interturn short circuit, immediately turn off the power.
- ⏱️ Startup and quick shutdown - thermal protection is triggered due to overload.
Safety precautions and precautions
Working with 220V electrical voltage requires increased concentration and compliance with all electrical safety standards. Remember that the compressor housing is metal and may become energized if the insulation breaks down. Therefore, it is highly advisable to use a grounded socket or ensure that the housing is grounded if the design allows it.
When you turn it on for the first time after repair or overhaul, do not leave the unit unattended. In the first minutes of operation, hidden defects may appear, such as sparking in the area of the relay contacts or rapid heating of the housing. Have on hand a fire extinguisher designed for extinguishing electrical installations.
Particular care should be taken when working with compressors removed from old refrigerators. They may use oil mixed with freon or retain residual pressure. Before any manipulations with the tubes, make sure that the pressure has been released and work in a well-ventilated area.
⚠️ Attention: It is strictly forbidden to check the tightness of the system or the operation of the compressor using an open flame. Refrigerants mixed with air can form explosive compounds.
Frequently asked questions (FAQ)
Is it possible to connect a compressor without a starting relay?
Theoretically, you can start the engine by manually applying voltage to the starting winding at the moment of switching on, but It cannot be used in this mode. Without a relay, the starting winding will burn out in a matter of seconds, since it is not designed for long-term operation under load.
What kind of capacitor is needed if a native one is not available?
The selection of a capacitor is carried out experimentally or according to tables for a specific type of engine. Typically the capacitance is 2-4 µF for every 100 watts of power. It is important that the operating voltage of the capacitor is at least 450V, otherwise it will swell or break.
Why does the compressor run for 5 minutes and turn off?
Most likely, the thermal protection relay is triggered. The reasons may be overheating due to poor ventilation, a malfunction of the relay itself, jamming of the mechanism or improper operation of the starting device, which does not turn off the starting winding.
How to determine whether the compressor or the relay has burned out?
Test the windings with a multimeter. If the resistance is infinitely high, there is a break (burnt out). If it is close to zero, there is a short circuit. If the resistance is normal, but the motor does not start and hums, most likely the problem is in the relay or mechanical jamming.
Is it possible to use a car compressor instead of a refrigeration one?
Car compressors (12V) and refrigeration compressors (220V) have different designs and power. Direct replacement is impossible without a complete rework of the power system and often the refrigeration line itself.