Start relay for a refrigerator: device, how to properly check and repair

The most necessary appliance, both in an apartment and in a private house, is a refrigerator.And it’s hard to disagree with this statement, isn’t it? It's difficult to find a home that doesn't have one. Like any appliance, refrigerators can break down. But there are situations when a breakdown can be diagnosed independently.

Almost all household refrigeration equipment is equipped with a single-phase motor. To start it you have to use a starting device. If this simple but important part fails, the compressor will no longer start. But, knowing the principles of operation of the device, you can identify the problem and fix it.

This article will talk about how the start relay for a refrigerator works and the signs of its malfunction. We will tell you how to troubleshoot refrigeration equipment. The videos we present will help you understand the principle of operation of the starting device, and also, if necessary, identify its malfunction.

Starting a single-phase asynchronous electric motor

At their core, compressor motors installed in modern refrigerators are single-phase asynchronous electric motors with a starting winding. Their main components are a rotating rotor and a stationary stator.

The rotor is a hollow cylinder made of conductive material or containing short-circuited wiring.

The stator includes two windings: working (main) and launcher (starting). They are mutually located at an angle of 90 degrees, or have the opposite direction of winding - the so-called “bifilar”. Alternating current passing through the main winding creates a magnetic field with a changing vector.

The pulsating field can be decomposed into two, rotating with the same period, but in opposite directions. This makes it easier to understand the physical essence of the process of influencing the rotor

If the rotor is not static, then, according to the law of electromagnetic induction, the motor will develop or decelerate torque, since the slip relative to the forward and reverse magnetic flux is different. Therefore, to maintain movement, alternating current passing through the working winding is sufficient.

If the rotor is stationary, then with the same slip relative to the magnetic fluxes, the resulting electromagnetic torque will be zero. In this case, it is necessary to create a starting torque. This is why a starting winding is needed.

The currents in the windings must be phase shifted, so a phase-shifting element is introduced into the motor - a register, inductor or capacitor. After the rotor reaches the required rotation, the supply of electricity to the starting winding stops.

Thus, to start a single-phase asynchronous electric motor, current must pass through two windings, and to maintain rotor rotation, only through the working winding. To regulate this process, a start relay is installed in the circuit in front of the refrigerator compressor.

The relay is located close to the compressor and in such a way that it can be easily removed. It is with checking this unit that one begins when the engine is running problematically.

Operating principle of the start relay

Despite the large number of patented products from various manufacturers, circuits refrigerator operation and the principles of operation of starting relays are almost the same. Having understood the principle of their operation, you can independently find and fix the problem.

Device diagram and connection to the compressor

The relay circuitry has two inputs from the power supply and three outputs to the compressor. One input (conditionally zero) passes directly.

The other input (conditionally – phase) inside the device is split into two:

• the first passes directly to the working winding;
• the second passes through the disconnecting contacts to the starting winding.

If the relay does not have a seat, then when connecting to the compressor you must not make a mistake with the order of connecting the contacts. Methods common on the Internet for determining winding types by measuring resistance are not correct in general, since some motors have the same resistance of the starting and running windings.

The electrical circuit of the start-up relay may have minor modifications depending on the manufacturer. The figure shows a diagram of the connection of this device in the Orsk refrigerator

Therefore, it is necessary to find documentation or disassemble refrigerator compressor to understand the location of the feed-through contacts.

This can also be done if there are symbolic identifiers near the outputs:

• "S" – starting winding;
• "R" – working winding;
• "C" - general exit.

The relays differ in the way they are mounted on the frame of the refrigerator or on the compressor.They also have their own current characteristics, so when replacing it is necessary to select a completely identical device, or better yet, the same model.

Closing contacts using an induction coil

An electromagnetic starting relay works by closing a contact to pass current through the starting winding. The main operating element of the device is a solenoid coil connected in series with the main winding of the motor.

At the moment the compressor starts, with the rotor static, a large starting current passes through the solenoid. As a result, a magnetic field is created that moves the core (armature) with a conductive strip installed on it, which closes the contact of the starting winding. The rotor begins to accelerate.

As the rotor speed increases, the amount of current passing through the coil decreases, as a result of which the magnetic field voltage decreases. Under the action of a compensating spring or gravity, the core returns to its original position and the contact opens.

On the cover of the relay with the induction coil there is an “up” arrow, which indicates the correct position of the device in space. If it is placed differently, then the contacts will not open under the influence of gravity

The compressor motor continues to operate in the mode of maintaining rotor rotation, passing current through the working winding. The next time the relay will work only after the rotor stops.

Regulation of current supply with a posistor

Relays produced for modern refrigerators often use a posistor - a type of thermal resistor.For this device, there is a temperature range below which it passes current with little resistance, and above which the resistance increases sharply and the circuit opens.

In a starting relay, a posistor is integrated into the circuit leading to the starting winding. At room temperature, the resistance of this element is insignificant, so when the compressor starts operating, current flows unhindered.

Due to the presence of resistance, the posistor gradually heats up and when a certain temperature is reached, the circuit opens. It cools down only after the current supply to the compressor is stopped and starts skipping again when the engine is turned on again.

The posistor has the shape of a low cylinder, which is why professional electricians often call it a “tablet”

Implementation of current type protection

An asynchronous motor is a complex electrical device that is prone to breakdowns. If a short circuit occurs, it will work circuit breaker, installed in switchboard.

If the fan, which cools the winding and mechanical moving elements, fails, the built-in thermal protection of the compressor will react.

The internal thermal protection of the electric motor is based on posistors. It responds to a general change in temperature inside the device, which can have both internal and external causes.

However, a situation may arise when the motor begins to consume 2-5 times more rated current for a long time (more than 1 second). Most often this occurs when there is an unplanned load on the shaft resulting from a jammed motor.

The current increases, but does not reach the short circuit values, therefore load-matched automatic won't work. There is also no reason for the thermal protection to turn off, since the temperature will not change in such a short period of time.

The only way to quickly respond to the situation and avoid melting of the working winding is to trigger the current protection, which can be installed in different places:

• inside the compressor;
• in a separate current protection relay;
• inside the start relay.

A device that combines the functions of turning on the starting winding and current protection of the motor is called a starting protection relay. Most refrigerator compressors are equipped with just such a mechanism.

The action of current protection is based on three principles:

• as the current increases, the resistance decreases and the heating of the conductive material increases;
• under the influence of temperature, the metal expands;
• The thermal coefficient of expansion differs for different metals.

Therefore, a bimetallic plate is used, which is welded from metal sheets with different expansion coefficients. Such a plate bends when heated. One end of it is fixed, and the other, deviating, opens the contact.

To heat a bimetallic circuit breaker, a coil is usually placed nearby through which electricity passes. Although sometimes they implement a “direct” version in the form of a conductive plate

The plate is designed for a temperature response when a current of a certain strength passes. Therefore, when replacing the start-up relay, it is necessary to check its compatibility with the installed compressor model.

Troubleshooting

Given the small number of relay elements, you can sequentially test them for functionality. To do this you will need a flathead screwdriver and a multimeter.

No. 1 - problems with relay operation

From a design point of view, a relay with a coil is a device with normally open contacts, and a posistor version is a device with normally closed contacts. Although in both cases there are possible options when, at start, there will be no current supply to the starting winding or, conversely, its shutdown will not work.

If the compressor is operational, but does not turn on following a command sent from the refrigerator control unit, this indicates a lack of voltage on the stator starting winding.

The reason for this may be:

• electrical circuit break;
• contact strip problem;
• posistor overheating;
• the electrical protection system is triggered and does not return to its normal position.

If the refrigerator turns on for 5-20 seconds and then turns off, then most often this is a consequence of the relay’s protective mechanism triggering.

The reasons may be the following:

• the protective mechanism is working properly, but the operation occurs due to problems in the working winding of the motor;
• the protective mechanism is working, but the relay does not open the contacts in the starting winding circuit;
• The protective mechanism is faulty, false operation occurs when the temperature is slightly overheated.

Since there may be several reasons for the malfunction, it is necessary to carry out a complete diagnosis of the start-up protection relay of the refrigerator.

The cost of start-up protection relays for brands such as Atlant or Biryusa does not exceed 500 rubles. If you quickly purchase and install a new working device, the refrigerator will not even have time to defrost

No. 2 - faulty electrical circuit contacts

A faulty start-up relay can be detected using a multimeter.

To do this, you need to ring three sections of the electrical circuit:

1. If there is a break in the area from the input to the output to the working winding, then it is necessary to check the location of the contact opening with the protective mechanism. It is possible that it worked and did not return to its original state or that the opening contacts were oxidized.
2. If there is no contact in the area from the input to the output to the starting winding, then in addition to a banal break in the conductor, two options are possible: opening the circuit by a protective mechanism or lack of contact through the bar.
3. A break in the straight (zero) section means mechanical damage to the chain - it is the easiest to find and fix.

If the relay operation is based on the use of an induction coil, then it is necessary to forcibly raise the bar - otherwise there will be no contact.

Using a multimeter, it is easy to detect faulty contacts by testing them through a resistance. It is important to take your time and check each section of the chain one by one.

No. 3 - incorrect operation of the posistor

To make sure that the posistor is working properly, you need to check it in a cold and heated state.

First of all, you need to wait until the posistor has cooled down (2-3 minutes in a non-working state is enough) and ring it with a multimeter. If there is no current or a high resistance is detected, the posistor is faulty and needs to be replaced.

If the device is working properly, then when checking it in a cold state, the multimeter should show the presence of slight resistance

To check the disconnection ability, you need to connect a consumer of electricity, for example, a hundred-watt incandescent lamp, to the posistor. To do this, you need an electrical plug with two terminals that are connected to the input of the device.The wires from the lamp are connected to the connectors leading to zero and the starting winding.

When the plug is plugged into the socket, the light will light up. Since the rating of the passing current in the experiment is significantly less than when starting the compressor, the posistor will heat up for a long time - for a hundred-watt lamp the response time will be 20-40 seconds.

If the light goes out after a while, then the device is working properly. If the consumer is not de-energized, this means that the posistor is not working. Repairing it at home is impossible, it is inexpensive, so you need to purchase an element with similar parameters.

No. 4 - problems with the contact strip

There are two types of contact strip problems:

• no current passes when the contacts are closed;
• The bar sticks and won't go down.

The first problem may arise due to oxidation of contacts. In this case, you need to clean them with sandpaper. Also, the reason may be the curvature of the position of the bar, then it is necessary to install it horizontally.

To clean the contacts and remove dirt or traces of oxidation, you can use fine sandpaper by placing it on a needle or thin flexible awl

A more difficult problem is the junction of the bar and the pin, which is affected by the magnetic field of the solenoid. The solution to the problem here is individual and depends on the type of malfunction.

Sticking of the strip is expressed in the fact that it does not come off along with the core. To do this, you need to clean the contacts to remove the adhesive and make them smooth.

No. 5 - abnormal operation of current protection

If, when ringing, a lack of contact is detected from the input to both windings, then most likely the break occurred in the protection zone.

In most cases, this is either a contact failure that opens the bimetallic plate, or damage in the area of ​​the heating coil.

The bimetallic plate and its heating coil must not be bent, displaced or otherwise carried out with them that would cause a change in the configured operation mode

If the damage cannot be corrected otherwise, you will have to purchase a new relay.

Conclusions and useful video on the topic

Video #1. Overview of the principle of operation, types and main faults of the start-up relay:

Video #2. Signs of failure of the common RKT starting relay. Connecting an external capacitor to compensate for unstable voltage:

The simple design of the starting relay allows you to independently find faults and easily fix them. This does not require deep electrical knowledge or special tools..

However, punctuality must be observed, since the functionality of expensive equipment depends on the quality of the work performed.

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