Operation of refrigeration equipment produced several decades ago often involves the need to manually adjust operating modes. Unlike modern models with digital controls and precise electronic sensors, older units rely on mechanical thermostats. Understanding the principles of their operation is necessary for every owner of such equipment to preserve food and extend the service life of the compressor.
Incorrect settings can lead to two extremes: either the products will begin to deteriorate due to insufficient cold, or the giant one will freeze, and the motor will wear out. In this article we will look in detail at how to find a balance, what tools you may need and what to look for when diagnosing. fur coat, and the motor will work for wear. In this article we will look in detail at how to find a balance, what tools you may need and what to look for when diagnosing.
The principle of operation of a mechanical thermostat
The heart of the temperature control system in older models (for example, Zil, Biryusa, Atlant) is the thermostat. This device is a sealed capsule filled with gas or liquid that expands or contracts depending on the surrounding temperature. Attached to this capsule is a long capillarywhich is attached to the evaporator inside the chamber.
When the temperature is temperature in the refrigerator falls, the gas in the capillary is compressed, and pressure is transferred to the thermostat membrane, opening the electrical contacts. The compressor turns off. As the temperature rises, the process occurs in the reverse order. The adjustment is carried out by changing the tension of the spring, which counteracts the gas pressure.
It is important to understand that the mechanics are not highly accurate. The error in ±2...3°C is considered normal for such systems. That is why owners have to periodically check the actual temperature using third-party devices.
⚠️ Attention! Before any manipulations with the electrical part of the thermostat, be sure to unplug the refrigerator. Even when the regulator is in the off position, voltage may be present at the contacts.
Location and marking of regulators
The appearance of regulators in old refrigerators may vary. Most often this is a rotary knob located inside the main camera or on the front panel. The scale may have numbers from 1 to 5, 1 to 7, or even designations like “Min” and “Max.”
The numbers on the handle do not mean degrees Celsius. They indicate the degree of cooling: the higher the number, the lower the temperature inside the chamber. Setting the knob to maximum (7 or Max) forces the compressor to work almost continuously, trying to reach a limit unattainable for this model.
In two-chamber models with one compressor, a system No Frost (or semi-automatic defrosting) is often used, where the cold is distributed over flaps. In such cases, the regulator can only control the freezer compartment, and in the refrigerator compartment the temperature depends on the air flow.
If your device has a separate “Freeze Mode” switch (usually red or with a snowflake), it forces the compressor on, ignoring the thermostat readings. You cannot keep it turned on for a long time - this will lead to icing.
Instrumental diagnostics and calibration
Since you cannot rely on sensations (“are your hands cold”), an external thermometer is required for precise adjustment. It is best to use a digital device with a remote probe that is capable of operating in a range of negative temperatures.
The calibration process is as follows: place the thermometer in a glass of water and place it on the middle shelf. Leave the refrigerator alone for several hours (preferably overnight) without opening the door. After that, take readings.
The optimal range for storing most products is +2...+5°C. If readings exceed these limits, intervention is required. In some models, a calibration screw is hidden under the regulator handle, turning which by a fraction of a turn can change the operating mode.
☑️ Checking the temperature mode
Table of correspondence of modes and symptoms
To quickly diagnose the condition of your refrigerator, use the following table. It will help determine which way the regulator needs to be turned or whether repairs are required.
| Regulator position | Symptom in the chamber | Compressor behavior | Recommendation |
|---|---|---|---|
| Minimum (1-2) | Food is thawing, no cold | It turns on rarely, does not work for long | Increase value |
| Average (3-4) | Stable cold, condensation moderate | Works cyclically (10 min / 20 min) | Leave as is |
| Maximum (6-7) | Vegetables freeze at the back wall | Works almost without stops | Reduce value |
| Any | Strong ice ("fur coat") | Long operating cycles | Check the seal and thermostat |
Please note that the operating and resting time of the compressor also depends on the ambient temperature (temperature in the room). In summer, when indoors +28°C, the refrigerator will work longer than in winter when +18°C.
Why does the refrigerator work worse in summer?
In summer, the difference between the temperature inside the chamber and outside reaches 30-40 degrees. The thermal insulation of older models is not ideal, so heat gain increases, and the compressor is forced to work almost continuously to compensate for the loss of cold. In winter, on the contrary, low temperatures are easier for him.
The influence of the external environment and loading
The temperature inside the refrigerator directly depends on how tightly the shelves are packed. An empty refrigerator cools down faster, but also heats up faster when the door is opened. A completely clogged unit allows cold air to pass through less easily, which can create “warm zones.”
It is important to leave gaps between the food and the back wall. It is located there evaporator, and if you block the access of air to it, the thermostat will “think” that the chamber is warm and will force the motor to work without interruption.
The location of the refrigerator itself in the room also plays a role. If it is located close to the battery or in direct sunlight, it will be almost impossible to adjust the normal temperature without damaging the service life of the equipment.
Frequent problems and their solutions
One of the common problems of older models is “sticking” of thermostat contacts or loss of bellows tightness. In this case, the regulator stops responding to turns of the knob. The compressor either does not turn on at all or hums continuously.
If you turn the knob, but the shutdown click is not heard for a long time (when the chamber is full), the thermostat may be faulty. Replacing it is an accessible procedure, but requires care when installing a new capillary tube.
⚠️ Attention! The thermostat capillary tube is very thin and fragile. When installing a new regulator, avoid sharp bends and impacts on the tube, otherwise the refrigerant inside it will come out and the device will stop working.
It is also worth checking the condition of the rubber seal on the door. If it becomes dry or dirty, warm air constantly enters the chamber. In this case, no amount of temperature adjustment will help - the compressor will thresh in vain.
Seasonal features of operation
Owners of old refrigerators, especially those installed in unheated rooms (dacha, garage, balcony), should be aware of the problem of winter startup. The oils in the compressor thicken at low temperatures, and the freon pressure drops.
It is not recommended to run a regular refrigerator at a temperature below +5°C . The thermostat may simply not turn on the engine, since it is “already cold,” or the compressor will try to start on thick oil and burn out. For such conditions, there are special climate classes of equipment.
If you need to use a refrigerator in the winter at the dacha, consider installing a winter kit (crankcase heating and drainage), although for older models this is often not economically feasible.
Is it possible to regulate the temperature in old refrigerators using external devices?
Yes, they exist external thermostats (socket thermostats) that cut into the power circuit. You set the desired temperature on the external unit, and it turns on and off the outlet into which the refrigerator is plugged in. This allows you to bypass a faulty internal thermostat or get a more accurate setting.
Why is it cold in the freezer, but warm in the refrigerator compartment?
In single-compressor models, the cold is produced in the freezer, and enters the refrigerator compartment through ducts. If the channels are clogged with ice (the defrost system is faulty) or the damper is stuck in the closed position, the cold will not reach the main chamber. This may also be a sign of a freon leak.
How often do you need to defrost an old refrigerator for normal operation?
Old models with manual defrosting require complete shutdown and defrosting when the layer of ice on the evaporator reaches 3-5 mm. This usually happens once every 3-6 months, depending on the moisture content of the food and how often the doors are opened. A thick layer of ice acts as a heat insulator, interfering with cooling.
What to do if the regulator knob rotates endlessly?
If the thermostat knob rotates in a circle without characteristic clicks or restrictions (“stops”), this may indicate a breakdown of the internal mechanism of the regulator. Most likely, the spring has burst or jumped off. In this case, adjustment is impossible - the unit must be replaced.