Hello, dear readers of Datagor.ru!
Today I will talk about my project, which was born due to the failure of one of the most important parts of my refrigerator - the thermostat. Automation stopped working and kept the refrigerator compressor on all the time, bringing the temperature inside to -4 ° C instead of the standard + 5 ° C! Minus temperature in the refrigerator, from the soup we get a piece of ice! And in the freezing part, it was generally under -25 ° C.

The time has come for me to study the principles of operation of refrigeration units and assemble my own digital thermostat, with indication, settings and protection of the compressor in time. We will talk about this further. Let's get started!

A bit of history

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Thank you for your attention!

Good! The freebie is over. If you want files and useful articles - help me!

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Thank you for your attention!
Igor Kotov, founder of Datagor magazine

It's hard to imagine your life without household appliances. There are appliances that we could do without, and there are those without which the arrangement of living space is rightfully considered inferior. One of these vital necessary items is a refrigerator. Do you agree?

Do-it-yourself home appliance repair is a good help for family budget. If desired, you can master many repair operations. For example, replacing a thermostat for a refrigerator is not so difficult. One has only to understand the design features and principles of operation of the device.

We will talk about how to detect a malfunctioning thermostat. The article we have proposed describes in detail how it is replaced during the repair of a Stinol brand refrigerator. The information is accompanied by a thematic selection of photo and video materials with expert advice.

The temperature regulator or thermostat is one of the main elements, without which the normal operation of the refrigerator is impossible. It captures the readings of the temperature sensors in the refrigerator and freezer and sends a signal to the compressor start relay.

According to these signals, the compressor turns on if the chamber is not cold enough, and turns off when the temperature reaches the set level. Technically, the thermostat is a relay, at one end of which there is a sealed tube filled with freon.

On the other hand, contacts are installed, the opening and connection of which sends a signal to the compressor. The end of the tube with freon, it is also called a capillary tube, is fixed on the evaporator.

The refrigerant placed inside is sensitive to heating and cooling. When the temperature drops or rises, the pressure inside the tube changes, causing the relay contacts to connect or open.

The movement of the contacts is controlled by a small spring. It is used to set the temperature level that should be inside the refrigerator compartment. A temperature control knob is attached to the spring. Turning this knob changes the tension of the spring.

As a result, more or less force is needed to close and open the contacts. This affects the level of pressure in the capillary tube at which the contacts actuate.

The thermostat is small device, which is equipped with a sealed tube with a sensor filled with refrigerant. Based on changes in the evaporator temperature, the relay switches the compressor on or off.

This regulates the degree of cooling of the air in the refrigerator. When using an electronic regulator, this process is carried out a little differently, but the principle remains approximately the same: desired level temperature is set on the basis of the actual values ​​recorded by the capillary tube.

But in such models, an electronic control module is used that can simultaneously manage data from several sensors. It is not always possible to repair or replace such a thermostat at home. Handling complex electronics requires knowledge and special equipment.

Typically, the thermostat is installed inside or outside the refrigerator compartment. Before starting the repair, it does not hurt to study the technical passport of the device. There may be many useful information by device specific model thermostat and its location.

Usually the thermostat is located next to the knob for setting the temperature. The internal arrangement is typical for relatively old models. Inside the chamber, the element is usually enclosed in a plastic protective case.

The adjustment knob is located right on it. To remove the thermal relay, you need to remove this handle and unscrew the fixing screws to remove the housing.

Do more modern models the thermostat is placed outside the chamber to save precious cubic centimeters of internal space and not spoil the design with additional elements

But you also need to look for the thermostat near the control knob, usually under the refrigerator body somewhere at the top. The handle is removed in the same way, the fasteners are unscrewed and they find what they are looking for behind the protective panel.

Ways to find the problem

If the thermostat is broken, this does not mean that the entire refrigeration unit will immediately stop working. But the lack of correct information about the current temperature will affect its operation.

Option # 1 - check the functioning of the equipment

Symptoms of incorrect operation of refrigeration equipment may include:

• the compressor runs without interruption or with very short and infrequent interruptions;
• the temperature inside the refrigerator chamber drops to zero, and sometimes even lower;
• appears on the walls a large number of frost or even ice;
• inside the refrigerator is too warm;
• the refrigerator does not turn on after being turned off, etc.

Of course, these signs can be associated not only with breakdowns of the thermal relay, but also with malfunctions of other elements.

To correctly determine the cause of the problems identified during the operation of a household refrigerator, you will need to conduct a small diagnostic. You can do it yourself

Option #2 - diagnostics with a thermometer

To do this, completely disconnect the refrigerator from the power supply, and then defrost it completely in accordance with the instructions. Of course, the contents will have to be removed.

After that, you need to turn on the device in the network and turn the thermostat setting knob to a position that will allow you to get the lowest possible temperature. If the refrigerator model has a freeze mode, it is recommended to use it.

To test the operation of the thermostat, you need to free the refrigerator from all products, place a thermometer inside the chamber and check its readings after a few hours

In the refrigerator compartment, approximately in the middle, you need to put a thermometer designed to measure the air temperature. It is better to use a device that allows you to take measurements below zero. The refrigerator is left in this mode for about two hours. After that, you need to check the thermometer readings.

If the temperature in the refrigerator compartment has dropped to about six degrees by this point, there are no problems with the thermostat. But when inside it became noticeably warmer or colder than this level, the thermostat will have to be replaced.

Option # 3 - visual inspection of the refrigerator chamber

If a so-called snow cap forms very quickly inside the chamber, the initial diagnosis of the health of the thermostat can be performed very simply.

The appearance of a snow coat in the refrigerator compartment almost always means that the thermostat is not working correctly, you need to diagnose its condition

To do this, at the time of compressor operation, the adjusting knob begins to turn in the direction of increasing the temperature inside the chamber. If the relay is working properly, at a certain moment the sensors will record the desired temperature level, after which the compressor will turn off. If the engine continues to run, the thermostat needs to be changed.

After such a diagnosis and with a working thermal relay, it is recommended to remove all contents from the chamber and let the device idle for about six hours. During this period, you need to pay attention to the duration of breaks in the operation of the compressor.

If it is about 40 minutes, everything is fine, you can use the refrigerator as usual. If the compressor turns on too often or rarely, you need to try to adjust this moment using the relay settings. If this fails, most likely, you will have to install a new thermostat.

Rules for dismantling the thermostat

If the refrigerator does not turn on at all, it will be impossible to carry out the diagnostics described above. Probable cause breakdowns can be called an electrical failure of this element.

But, for example, a burnt motor winding can also become a problem. To understand if the thermostat needs to be replaced, it will have to be removed from the refrigerator for examination.

Usually the thermostat is located next to the adjusting knob, with which the air temperature in the refrigerator is set. Two-chamber models are equipped with a set of two such handles

First you need to unplug the refrigerator. Now you should find the place where it is located, as described earlier. Usually you need to remove the adjustment knob, remove the fasteners and remove the protective elements.

Then you need to carefully inspect the device, paying close attention to the wires through which the power supply is connected.

All of them have different color coding depending on destination. Usually, a yellow wire with a green stripe is used for grounding. This cable should be left alone, but all the others should be disconnected and shorted to each other.

Now the refrigerator is turned on again. If the device still does not turn on, the thermostat is probably working, but there are serious problems with the compressor.

If the refrigerator does not turn on at all, the cause may be not only a malfunction of the thermal relay, but also a compressor breakdown, for example, a blown motor winding

If the engine is running, we can make an unambiguous conclusion that the relay needs to be replaced. Before starting work, it does not hurt to arm yourself with a smartphone or camera in order to consistently record all operations. When installing a new thermostat, these images can be very helpful, especially for beginners.

It is necessary to clearly remember which cable core was used for what purposes. Usually, a black, orange or red wire is used to connect the thermal relay to the electric motor. A brown wire leads to zero, a yellow-green wire provides grounding, and a pure yellow, white or green wire is connected to an indicator light.

To connect the thermal relay, wires with different color markings are used, you need to remember the purpose of each wire so as not to be confused during reassembly

Sometimes it can be difficult to remove a damaged regulator, especially when it is placed outdoors. For example, in some models of Atlant refrigerators, you have to completely remove the chamber door from its hinges. To do this, remove the trim, which is installed above the upper hinge, and unscrew the bolts hidden under it.

Before you remove the adjustment knob, you also have to remove the plugs and unscrew the fasteners. All these operations must be done carefully. Fasteners and linings are best stored in a small container so that they are not lost. The thermostat itself is usually screwed to the bracket, it must be carefully removed, unfastened and removed.

If the thermostat is located inside the refrigerator compartment, it is usually hidden under a plastic casing, where a lamp for lighting can also be mounted.

A new thermostat is installed in its place, following the reverse assembly order. Sometimes the breakdown of the thermostat is associated with a malfunction of the so-called capillary tube or bellows. If you replace only this element, the relay can be left.

To perform this procedure, you will have to remove the thermal relay, following the method described above. The bellows must be disconnected from the evaporator and carefully removed from the device housing. Now install a new capillary tube, attach it to the evaporator, and mount the relay in its original place, and connect the disconnected wires.

Replacement using the example of a refrigerator Stinol

For relay failure, it is a fairly common occurrence, especially after five to seven years of operation.

Most often, the bellows tube fails here, since it is this option that is laid down by the manufacturer of this element. The Stinol-101 ​​model has only one compressor, but in Stinol-103 there are two of them: separately for the refrigerator and freezer.

This is a K-59 type thermal relay contact diagram, which allows you to get an idea of ​​which wires should be connected where. Color coding may differ, photos on the phone will help save information, you can also draw a similar diagram yourself

Automation different models slightly different, which is reflected in the corresponding electrical diagrams, otherwise these refrigerators are very similar, so it makes sense to consider the procedure for repairing them at the same time.

To understand that the Stinol refrigerator needs repair or replacement of the thermostat, you need to pay attention to the following signs:

• the compressor runs non-stop and does not respond when the regulator is set to OFF;
• when the adjusting knob is turned to the OFF mark, there is no characteristic click;
• the temperature in the refrigerator chambers significantly exceeds the parameters set during the adjustment.

The K-59 thermal switch is used in the Stinol-103 refrigerator, it is easy to check the marking, it is indicated on the case. To remove the adjustment knobs, you need to use a thin awl. They just need to be put on and taken off. Stinol-101 ​​has only one adjustment knob, while Stinol-103 has two, one for each compressor.

To remove the adjustment knob of the Stinol refrigerator (1), you need to use some sharp object, such as an awl. Then remove the decorative trim (2), which is held by four protrusions

After the handle is removed, you need to remove the decorative overlay, which has six protrusions. This is a fragile item, you should be careful not to damage it. Under the lining are nuts that should be unscrewed. After that, you need to unscrew the screws that fix the control panel.

Under the decorative trim there are fixing screws (1) that hold the thermostat in the correct position, they must be unscrewed in order to continue dismantling the element

The screws holding the refrigerator door hinge should be removed last. To avoid possible damage, the door must be held. Now you can lift the panel and remove the door from its hinges.

The next step is to remove the top cover of the refrigerator.

The fasteners that fix the control panel and the door hinge (1) of the Stinol refrigerator must be unscrewed moving towards the door, and not away from it

The necessary fasteners are located on the back side. Unscrew them and remove the cover. Thus, free access to the thermostat will be obtained.

First you need to disconnect the relay contact connectors, after which you can remove the element from the refrigerator control panel.

After the doors are removed and top panel refrigerator Stinol, you can carefully remove the thermostat for inspection and diagnosis

At this stage, you need to remember or write down the color marking of individual wires. To remove the worn capillary tube, remove the plastic cover.

Now you need to unscrew the fixing screw and remove the lighting unit. The tube is removed through the hole provided for this.

To continue replacing the thermostat in the Stinol refrigerator, remove the cover (1) in the refrigerator compartment and remove the capillary tube (2)

The new element is installed in such a way that the non-insulated area in its lower part is securely hidden under the overlay. The hole is closed with a plastic plug to restore the tightness of the chamber.

Typically, the capillary tube protrudes beyond the temperature controller. It must be carefully placed under top cover refrigerator, there is enough space.

To remove the capillary tube (2) and replace it, you must first disconnect the lighting unit, which is fixed with a screw recessed into its housing

Now you need to reassemble the thermostat and refrigerator: connect all the necessary connections, install and secure the refrigerator cover, hang the door.

And again, the screwing of the door hinge fasteners is performed last, when the rest of the similar screws are already installed.

The hole that is formed on the back panel during the repair work should be sealed with plastic to restore the tightness of the refrigerator compartment

To check the status of the Stinol refrigerator thermostat at home, you can use a simple diagnostic. Contacts 3 and 4 of such a device should remain closed at room temperature.

If, after connecting them with a jumper, the compressor is turned on, the thermostat is faulty, it needs to be replaced. If the thermostat settings are wrong, they can be corrected by turning the adjusting screws, but this should be done in service center with the necessary equipment.

An equally important functional unit in the design of the refrigerator is, with the device, purpose and methods of repair of which the article recommended by us will acquaint.

The procedure for replacing the thermostat cannot be called too complicated. However, improper handling of this element can only worsen the situation. A detailed study of the repair procedure and attention to detail will help restore the refrigerator to working order.

Tell us about how you selected a thermostat to restore the refrigerator to working capacity. Share useful information and valuable information on the topic of the article that can be useful to site visitors. Please leave comments, post photos and ask questions in the block below.

Simple refrigerator thermostat

Make a Simple Refrigerator Thermostat Circuit

Want to make an accurate electronic thermostat for your refrigerator? The solid state thermostat circuit described in this article will surprise you with its "cool" performance.

Introduction

A device, once built and integrated with any suitable device, will instantly begin to exhibit improved system control, saving energy, as well as increasing the life of the device. Conventional refrigeration thermostats are expensive and not very accurate. Moreover, they are subject to wear and therefore are not permanent. A simple and efficient electronic refrigeration thermostat is discussed here.
A thermostat, as we all know, is a device that is able to perceive a certain set temperature level and turn off or switch an external load. Such devices may be electromechanical types or more complex electronic types.
Thermostats are usually associated with air conditioning, refrigeration and water heating devices. For such applications, the device becomes an important part of the system, without which the device can reach and start working in extreme conditions and eventually get damaged.
Adjusting the control switch provided in the above devices ensures that the thermostat turns off the power to the device after the temperature crosses the required limit and switches back as soon as the temperature returns to the lower threshold.
Thus, the temperature inside refrigerators or room temperature through the air conditioner is maintained in favorable ranges.
The refrigeration thermostat circuit idea presented here can be used externally above a refrigerator or any similar device to control its operation.
Controlling their operation can be done by attaching a thermostat sensing element to an external heat sink, usually located behind most refrigerant units that use freon.
The design is more flexible and wider than built-in thermostats and is able to show better efficiency. The circuit can easily replace conventional low-tech designs, and besides, it is much cheaper compared to them.
Let's understand how the circuit works:

Circuit Description
A simple refrigerator thermostat circuit

The diagram shows simple circuit built around IC 741 which is basically configured as a voltage comparator. It uses a lower power transformer to make the circuit compact and solid state.
The bridge configuration containing R3, R2, P1 and NTC R1 at the input forms the main sensing elements of the circuit.
The inverting input of IC is clamped to half the supply voltage using the voltage divider network R3 and R4.
This eliminates the need to provide dual power to the IC and the circuit can provide optimal results even with a single supply voltage.
The reference voltage to the non-inverting input of IC is clamped across a given P1 with respect to NTC (Negative Temperature Coefficient).
In the event that the temperature under control tends to drift above the desired levels, the NTC resistance drops and the potential at the non-inverting input of IC crosses the set value.
This instantly switches the output of the IC, which in turn switches the output stage containing the transistor, the triax network, turning off the load (heating or cooling system) until the temperature reaches a lower threshold.
Feedback resistance R5 to some extent helps to induce hysteresis in the circuit, important parameter, without which the circuit can spin rapidly in response to sudden changes in temperature.

Once the assembly is completed, setting up the circuit is very simple and is done with the following points:

REMEMBER EXTERNAL CIRCUIT BASED ON CONSTANT SOURCE POTENTIAL, CAUTION WARNING IS WARNED TO AGAINST TESTING AND INSTALLATION PROCEDURES. THE USE OF A WOOD PLANK OR ANY OTHER INSULATING MATERIAL ON YOUR FOOT IS STRONGLY RECOMMENDED; ALSO USE ELECTRIC TOOLS WHICH SHOULD BE INSULATED NEAR THE SITE.

How to set up this electronic refrigeration circuit thermostat You will need a sample heat source finely adjusted to your desired cutoff threshold level for the thermostat circuit.
Turn on the circuit and enter and attach the above heat source to the NTC.
Now adjust the preset so that the output just switches (the output LED lights up). Remove the heat source from the NTC, depending on the hysteresis of the circuit, the output should turn off within a few seconds.
Repeat the procedure many times to confirm its correct functioning.
This completes the setup of this refrigeration thermostat and is ready to be integrated with any refrigerator or similar device for precise and constant regulation of its operation.

Parts list

R2 = Preset 10KR3,

R9=56ohm/1watt

C1 = 105 / 400V

C2 = 100uF / 25V

Z1 = 12V, 1W zener diode

* option via optocoupler, added switch and diode bridge to the power supply

How to create an automatic refrigerator temperature controller circuit

The idea for this circuit was suggested to me by one of the keen readers of this blog, Mr. Gustavo. I posted one similar circuit for an automatic refrigerator thermostat, however the circuit was intended to define more high level temperature available at the back of the refrigerator grille.

Introduction

Mr. Gustavo didn't quite get the idea and he asked me to design a refrigerator thermostat circuit that could sense cold temperatures inside the refrigerator rather than hot temperatures at the back of the refrigerator.
So with some effort I could find a real Fridge Temperature Controller CHAIN ​​DIAGRAM, let's explore this idea with the following points:
How circuits function
The concept is not very new nor unique, it is the usual comparator concept that has been included here.

IC 741 has been rigged in standard comparator mode and also as a non-inverting amplifier circuit.
The NTC thermistor becomes the main sensing component and is specially responsible for cold temperature sensitivity.
NTC means negative temperature coefficient, which means that the resistance of the thermistor will increase as the temperature around it drops.
It should be noted that the NTC must be rated according to these specifications, otherwise the system will not function properly.
The preset P1 is used to set the trip point of the IC.
When the temperature inside the refrigerator falls below the threshold level, the thermistor resistance becomes high enough and reduces the voltage across the inverting pin below the non-inverting pin voltage level.
This instantly makes the IC output high, activating the relay and turning off the refrigerator compressor.
P1 should be set so that the output of the op-amp goes high at zero degrees Celsius.
The slight hysteresis introduced by the circuit comes as a boon, or rather a blessing in disguise, because it causes the circuit to not switch quickly at threshold levels, but only reacts after the temperature has risen about a couple of degrees above the shutdown level.
For example, suppose if the trigger level is set to zero, the IC will turn off the relay at that point, and the refrigerator compressor will also be turned off, the temperature inside the refrigerator will now start to rise, but the IC will not switch immediately, but maintains its position as long as the temperature will not rise to at least 3 degrees Celsius above zero.


If you have further questions regarding this automatic refrigerator temperature controller circuit, you can express the same through your comments.

RP1, RP2 regulation can be set temperature control points, 555 time Schmitt circuit inversion circuit, using relays to achieve automatic control.

The electronic thermostat for refrigerator will help in cases where your own (factory) thermostat is faulty or its accuracy is no longer sufficient. Older refrigerators use a mechanical temperature thermostat using a liquid or gas filled capillary.

When the temperature changes, the pressure inside the capillary also changes, which is transferred to the membrane (bellows). As a result, the thermostat turns the refrigerator compressor on and off. Of course, similar system temperature control has a low accuracy, and its parts wear out over time.

Description of the operation of the thermostat for the refrigerator

As you know, the temperature of food storage in the refrigerator should be + 2 ... 8 degrees Celsius. The operating temperature of the refrigerator is +5 degrees.

The electronic thermostat for the refrigerator is characterized by two parameters: the start and stop temperature (or the average temperature plus the hysteresis value) of the compressor. The hysteresis is necessary to prevent the refrigerator compressor from turning on too often.

This circuit provides a hysteresis of 2 degrees at an average temperature of 5 degrees. Thus, the refrigerator compressor turns on when the temperature reaches + 6 degrees and turns off when it drops to + 4 degrees.

Material: ABS + metal + acrylic lenses. LED lights...

This temperature range is sufficient to maintain the optimal storage temperature of the food, and at the same time it ensures comfortable operation of the compressor, preventing its excessive wear. This is especially important for already old refrigerators that use a thermal relay to start the engine.

The electronic thermostat is a suitable replacement for the original thermostat. The thermostat reads the temperature using a sensor, the resistance of which changes depending on the change in temperature. The thermistor (NTC) is often used for these purposes, but the problem lies in its low accuracy and the need for calibration.

To ensure accurate setting of the controlled temperature and avoid many hours of calibration, in this option refrigerator thermostat has been selected. It is an integrated circuit, linearly calibrated in degrees Celsius, with a factor of 10 mV per degree Celsius. Due to the fact that the threshold temperature is close to zero, the relative change in the output voltage is large. Therefore, the signal from the output of the sensor can be controlled using a simple circuit consisting of only two transistors.

Because output voltage too little to open the transistor VT1, the LM35 sensor is turned on as a current source. Its output is loaded with a resistor R1 and therefore the current on it changes in proportion to the temperature. This current causes a drop across resistor R2. The voltage drop controls the operation of the transistor VT1. If the voltage drop exceeds the threshold voltage of the base-emitter junction, transistors VT1 and VT2 open, relay K1 turns on, whose contacts are connected instead of the contacts of the old thermostat.

Resistor R3 creates a positive feedback. This adds a small current to R2, which shifts the threshold and thus provides hysteresis. The winding of the electromagnetic relay must be rated for 5 ... 6 volts. The contact pair of the relay must withstand the required current and voltage.

The LM35 sensor is located inside the refrigerator in a suitable location. The resistance R1 is soldered directly to the temperature sensor, which in turn allows you to connect the LM35 to the circuit board with just two wires.

The wires connecting the sensor can introduce interference into the circuit, so capacitor C2 is added to suppress interference. The circuit is powered by a built-in 5 volt power supply. The current consumption mainly depends on the type of relay used. must be securely isolated from the network.

The big advantage of this circuit is that it starts working immediately at the first start and does not need to be calibrated and adjusted. If it becomes necessary to slightly change the temperature level, then this can be done by selecting the resistances R1 or R2. Resistance R3 determines the amount of hysteresis.

Do-it-yourself refrigerator thermostat

It all started with the fact that after returning from work and opening the refrigerator found it warm. Turning the thermostat knob did not help - the cold did not appear. So I decided not to buy. new block, which is also rare, and make an electronic thermostat on the ATtiny85. With the original thermostat, the difference is that the temperature sensor is on the shelf, and not hidden in the wall. In addition, 2 LEDs appeared - they signal that the unit is on or the temperature is above the upper threshold.

Device Diagram:

To connect, it was necessary to conduct a second 220 V wire (taken from a lighting lamp) to power the transformer.

The connector to which the potentiometer is connected is also the ISP programming connector.

The board is protected from moisture with a special varnish for printed circuit boards.

The transformer here is 6 V. It was chosen to minimize losses on the 7805 chip.

The relay here can also be put on 12 V. If you take the voltage to it to the stabilizer. To reduce costs, it would be possible to create a transformerless power supply, although there are supporters and opponents of such a solution (electrical safety). Another cost cut is the elimination of the AVR microcontroller. There are Dallas thermometers that can also work in thermostat mode.