Restoring the functionality of the refrigeration unit often requires replacement or reconnection compressors, which is one of the most important operations in household repairs. Incorrect connection of the start relay contacts or a violation of the sequence of actions can lead to instantaneous failure of an expensive motor, a short circuit or even a fire. Before starting any work, it is necessary to clearly understand the principle of interaction between the motor windings and the protective starting automation.
Modern single-phase asynchronous motorsused in refrigerators cannot start on their own without an external push, which creates a rotating magnetic field. It is for this process that the starting relay is responsible, which briefly connects the starting winding and then turns it off when the rotor reaches the required speed. Understanding this process physics is the key to successfully and safely connecting equipment to a 220V power supply.
In this article we will examine in detail the stages of diagnostics, preparation and direct connection of the compressor, paying special attention to the connection diagrams of various types of relays. You'll learn how to correctly identify winding terminals, test insulation integrity, and assemble a working circuit that will last for many years. Compliance with safety precautions when working with high voltage is an absolute priority.
The principle of operation of the starting relay and motor windings
The basis of the starting system is starting relay, which can be electromagnetic or posistor. In electromagnetic models, the current passing through the main winding creates a magnetic field that draws in the core and closes the contacts of the starting circuit. As soon as the engine speed increases, the current drops and the spring opens the contacts, turning off the starting winding. PTC relays operate on the principle of changing the resistance of a ceramic element when heated by current.
The compressor itself has two main windings: working (main) and starting. The working winding has a thicker wire and less resistance; it is constantly involved in the operation of the engine. The starting winding is made of thinner wire, has a higher resistance and is turned on only at the moment of start, which is usually less than a second. Incorrect identification of these terminals is the most common mistake of beginners.
⚠️ Attention: If you mix up the starting and working windings when connecting, the engine may hum, but not start, or quickly burn out due to overheating of the thin wire of the starting winding, which is not designed for long-term operation.
A protective relay, often combined with a starting relay in one housing, is used to turn off the power in case of overcurrent or overheating of the compressor housing. Inside it is a bimetallic plate that bends when heated and opens the circuit. This is a critical element that prevents insulation fire and destruction of the motor when jammed or power surges in the network.
Diagnostics and preparation of equipment
Before proceeding with installation, you need to make sure that the motor itself is in good working order compressor and that there are no interturn short circuits. To do this, you will need a multimeter set to measure resistance (Ohms). The first step is to check the resistance between the terminals of the windings: the sum of the resistances of the starting and operating windings should be approximately equal to the resistance between the common contact and the contact where they are connected internally.
It is also critical to check the absence of breakdown on the housing. One multimeter probe is applied to any copper fitting or stripped part of the housing, and the second to the terminals of the windings. The device should show infinity (one in the most significant digit). If you see any resistance values, this means a violation of the insulation, and operating such a unit is strictly prohibited due to the risk of electric shock.
Visual inspection of the starting relay is also required. If it is an electromagnetic relay, there should be no burning smell inside, and the contacts should be clean. The posistor element must not have cracks or chips. Sometimes the cause of the malfunction is not the compressor itself, but oxidized contacts in the block or a break in the wires going to the thermostat.
To carry out the work you will need the following set of tools:
- 🛠️ Multimeter with continuity and resistance measurement function.
- 🔧 Set of screwdrivers and pliers for dismantling fasteners.
- ⚡ Insulating materials (insulating tape, heat shrink) and terminal blocks.
- 🧤 Dielectric gloves for protection against accidental electric shock.
☑️ Diagnostics before connection
Connection diagram and contact identification
A terminal block with three terminals is usually located on the top of the compressor. In most modern models they are arranged in a triangle. To correctly identify them without marking, you need to know the rule: the greatest resistance will be between the starting and working terminals, the smallest - between the working and common, and the average value - between the starting and common.
Consider the classic connection diagram via electromagnetic relay. The common wire (Common) goes directly to the network through the thermostat. The working winding is constantly connected to the network. The starting winding is connected to the network only through normally open relay contacts. It is important to follow the sequence: first, the current flows through the relay coil and the working winding, creating a magnetic field for starting.
For posistor relays, the circuit is even simpler, since they do not have moving mechanical parts. The posistor is connected in series with the starting winding. When cold, its resistance is low and current flows freely, starting the engine. When heated, the resistance increases sharply, actually breaking the starting winding circuit, which is required for normal operation of the engine.
| Output type | Designation | Resistance (approximate) | Function |
|---|---|---|---|
| Common | C | - | Winding connection point |
| Working (Run) | R | 10-25 Ohm | Main operation of the engine |
| Starting (Start) | S | 20-50 Ohm | Starting the rotor |
When assembling the circuit, make sure that all connections are made securely. The use of twists in the power circuits of the refrigerator is unacceptable, since vibrations of the compressor can weaken the contact, which will lead to sparking and heating. It is best to use original terminal blocks or high-quality connectors with locking.
What to do if the markings are erased?
If there are no markings on the relay or compressor housing, use the elimination method. Find a pair of contacts with maximum resistance - these will be the starting and working terminals. The third contact is general. To understand which is which, measure the resistance from the total to the other two: where less is the working winding, where more is the starting winding.
Step-by-step instructions for assembling the circuit
The connection process begins with installing the relay on the compressor terminals. It is put on with force until it stops, it is important not to confuse the orientation (usually the “UP” marking should face up). Then the wires from the thermostat and the power plug are connected to the relay contacts. Observe the color coding of the wires, if present, so as not to get confused in the future.
Next, you need to organize proper grounding. The compressor housing and the metal body of the refrigerator must be grounded, especially if the appliance is used in conditions of high humidity or without an RCD in the panel. This will ensure the drainage of static electricity and protect the user in case of insulation breakdown.
After connecting all electrical circuits, do not rush to immediately close the casing. It is better to carry out the initial start-up in “field” conditions, providing access to the compressor for visual and auditory control. Plug in the refrigerator and carefully monitor the startup process.
- 🔊 The engine should start with a characteristic hum, turning into a smooth hum.
- ⚡ There should be no bright sparking in the area of the relay or brushes (if any).
- 🌡️ Through After 10-15 minutes of operation, the capacitor tube should begin to heat up.
- 🔄 The relay should clearly click when the starting winding is turned off (for electromagnetic ones).
Typical errors and methods for eliminating them
One of the most common mistakes is installing a relay of the wrong model. Even if it physically fits onto the contacts, its current characteristics may not match the motor parameters. This will either result in the relay not turning off the starting winding (and it will burn out), or the engine will not be able to start.
Ignoring the state of the contacts is another problem. Oxidized or burnt contacts create additional resistance, causing heating and voltage drop across the windings. The engine may hum, jerk, but not develop full speed, which will ultimately lead to the thermal protection relay tripping.
⚠️ Attention: If, after turning on, the compressor hums, but does not start, and after a few seconds the shutdown click is heard, immediately turn off the power. This is a sign of a jammed mechanism or a malfunction of the starting system. Repeated starts can finish off the engine.
They also often forget about the capacitor if it is provided for in the design (usually in powerful models or models with low starting torque). A faulty capacitor will prevent the engine from developing the required torque. It can only be checked with a special device or by replacing it with a known good one.
Here is a table of the main symptoms and their causes:
| Symptom | Probable cause | Solution |
|---|---|---|
| Humming, won’t start | Relay jammed or malfunctioning | Replacing the relay, checking the mechanics |
| Quiet humming, silent | Open circuit or burnt winding | Testing with a multimeter |
| Knocks out the machine | Short circuit or breakdown | Checking the insulation on the body |
Safety precautions and final checks
Working with 220V electricity requires maximum concentration. All manipulations to connect the wires should be carried out only with the refrigerator completely disconnected from the network. Do not rely on the switch in the socket - it is better to pull out the plug or turn off the machine in the panel.
After assembling the circuit and a successful test run, it is necessary to fix all connections. The wires should not touch the hot compressor tubes or moving parts (if we are talking about a fan, although in this topic we are talking about piston groups). Use plastic clamps and clips to lay the harness.
The final step is to install the compressor protective casing. It not only protects from dust and moisture, but also directs air flow for proper engine cooling. The absence of a casing can lead to overheating and frequent shutdowns by the thermal relay.
Remember that parameters and connection requirements may vary depending on the manufacturer (Indesit, Bosch, LG, Atlant) and year of manufacture of the equipment. Always check the technical documentation or the diagram pasted on the back wall of the refrigerator, if it is preserved.
Is it possible to connect the compressor directly without a relay?
Theoretically, you can start the engine by manually applying current to the starting winding, but it will not be able to operate in this mode. Without a relay, the starting winding will remain on, quickly overheat and burn out. Operation without a relay is impossible.
Why does the compressor start and immediately turn off?
This may indicate the operation of a thermal protection relay. Reasons: overheating, jamming of the piston group, low voltage in the network or malfunction of the protective relay itself. An interturn short circuit is also possible.
How to determine whether the compressor has burned out?
You need to test the windings with a multimeter. If the resistance between any terminals is zero (short circuit) or infinity (break), the motor is faulty. Also a sign is a breakdown on the housing.
Is it necessary to change the drying filter when connecting?
If the refrigerator system was opened (there was a freon leak), replacing the filter-drier is required. If you change only the electrical part (relays, wires) without breaking the tightness of the circuit, you do not need to change the filter.