Owners of Soviet and post-Soviet equipment are often faced with the need to fine-tune the operation of the unit, especially when it comes to models released several decades ago. Biryusa refrigerator has proven itself to be a reliable technology, but over time, mechanical components require intervention to restore optimal cooling modes. Understanding the principles of operation of the thermostat allows you not only to extend the service life of the compressor, but also to ensure proper storage of products.
Modern users, accustomed to electronic panels, may be confused when they find in older models only a rotary knob or a screw under a seal. However, it is the mechanical adjustment that is distinguished by its high maintainability and stability. In this article we will analyze the nuances of setting thermostats T-133 and TAM-133, which were most often installed in units produced in Krasnoyarsk.
It is important to immediately note that intervention in the structure requires care. Incorrect settings can lead to the compressor working without stopping or, conversely, turning on rarely, causing spoilage of products. A critically important parameter is the temperature difference between turning on and off the compressor, which in older models can be up to 10-12 degrees Celsius. Let's look at the device and adjustment methods in more detail.
The principle of operation of a mechanical thermostat
The basis of the temperature control system in old Biryusa models is a thermostat - a device that opens the electrical circuit when a given cold threshold is reached. Inside the device body there is a bellows (sealed corrugated chamber) filled with freon or refrigerant with similar properties. When the temperature in the fridge compartment changes, the pressure inside the bellows changes, which leads to mechanical compression or expansion.
This movement is transmitted to a system of levers that open or close the electrical contacts that control the compressor. Temperature adjustment is carried out by changing the tension force of the spring, which counteracts the pressure in the bellows. By turning the knob on the front panel or the screw on the thermostat body, you change the force required to open the contacts.
⚠️ Attention: Thermostats of older models (especially the T-133 series) are position sensitive. If the refrigerator was heavily tilted during transportation, oil from the compressor or condensation could get into the capillary tube of the thermostat, which will lead to incorrect readings.
There are two main types of adjustment: external (knob from 1 to 5 or 7) and internal (screws on the thermostat housing). The outer knob changes the tension of the main spring, shifting the temperature range. Internal screws allow you to adjust the switching point and temperature difference (differential). Fine adjustments often require access to internal screws, which involves removing the casing.
Diagnostics of current cooling performance
Before turning any screws, you need to understand the real state of affairs inside the chambers. An eye meter will not help here, since the products may look normal even if the conditions are incorrect, but their shelf life will be significantly reduced. For diagnostics, you will need a household thermometer capable of measuring negative temperatures.
The measurement process must be static. Place the thermometer in a glass of water on the middle shelf of the refrigerator and close the door. Leave the unit to operate normally for at least 2-3 hours without opening the door. Only after this can readings be taken. In the freezer, measurements are carried out similarly, but between layers of frozen food.
The normal mode for the refrigerator compartment of old Biryus is considered to be a range from +2 to +6 degrees Celsius. In the freezer, the temperature should drop to -18 degrees or lower. If you see significant deviations, for example, +10 in the refrigerator compartment or a complete lack of frost in the freezer while the compressor is running, intervention in the settings is required.
Pay attention to the compressor operating cycle. In a working refrigerator, it should take up approximately 30-40% of the total time (for example, it works for 10 minutes, rests for 20). If the unit hums constantly or turns on too rarely (once every 2-3 hours), this is a signal of a failed thermostat adjustment or a freon leak.
External adjustment: thermostat knob
The easiest way to influence the temperature is to use a rotary knob located inside the refrigerator compartment or on the front panel. On older Biryusa models, the scale is usually graduated from 1 (minimum cold) to 5 or 7 (maximum). It is important to understand that the numbers do not correspond to degrees, but only indicate the degree of spring tension.
If the food in the refrigerator compartment freezes at the back wall and the compressor rarely works, you should turn the knob towards lower values. And vice versa, if the chamber is warm and the motor hums almost without interruption, you need to add a mode. However, if when turning the knob towards the maximum the compressor does not turn off for hours, the problem may not be in the settings, but in a refrigerant leak or wear on the compressor.
A situation often occurs when the knob turns too easily or, on the contrary, is jammed. In the first case, the control lever could come off, in the second, the contacts could oxidize or the lubricant could dry out. To check the mechanism, sometimes you have to remove the plastic handle by pulling it towards you and inspect the thermostat rod.
☑️ Initial setting of the handle
Fine tuning through the adjusting screws
For more accurate calibration, especially if the knob does not give the desired result, use the internal thermostat adjustment. Thermostat housings T-133, TAM-115 and analogues usually have two screws. One screw (often under the seal) is responsible for the opening (switching off) temperature, the second - for the closing (switching on) temperature or range.
To gain access to the screws, you need to remove the thermostat casing. Attention: Before starting work, be sure to disconnect the refrigerator from the power supply! The screws are typically small and will require a thin slotted screwdriver to get the job done. Turning the screw clockwise usually increases the spring tension, increasing the shutdown temperature (the unit will freeze more strongly).
Adjustment is made with microscopic movements. It is enough to turn the screw 1/8 or 1/4 turn, and then let the refrigerator sit for several hours. Sharp turns can cause you to “overshoot” the desired range and have to start over. Remember the original position of the screws or make marks with a marker before starting adjustment.
⚠️ Attention: Do not try to adjust the screws if you are not sure that the thermostat is working properly. If the bellows has lost its tightness, twisting the screws will not have any effect, but will only disrupt the factory settings, after which the device will have to be changed completely.
Table of settings and temperatures
Understanding how the position of the regulator affects the operation of the system helps you quickly find the optimal mode. Below is an indicative table for standard operating conditions (room temperature +20...+25°C). It is worth remembering that as a refrigerator ages, the insulation of the refrigerator deteriorates, and higher settings may be required to maintain the same temperature.
| Handle position | Temperature in the refrigerator compartment (approx.) | Temperature in the freezer compartment | Compressor operating mode |
|---|---|---|---|
| 1 (Min) | +8...+10°C | -6...-8°C | Short cycles, long pause |
| 3 (Avg.) | +4...+6°C | -12...-15°C | Normal cycle (1:3) |
| 5 (Max) | +1...+2°C | -18...-24°C | Long work |
| 6-7 (Freezing) | 0...+2°C | Below -24°C | Almost non-stop |
The table shows that the maximum values are intended for quick freezing of fresh food and not for continuous operation. Long-term operation in modes 6-7 leads to accelerated wear of the compressor and excessive freezing of the “coat” on the evaporator, which, in turn, worsens heat transfer.
Why do foods at the rear wall freeze in mode 5?
This is a characteristic feature of old refrigerators with a drip defrosting system. The evaporator is located at the back wall, and the temperature there is always below the average in the chamber. Store sensitive products (eggs, milk) on the door or in the middle part of the shelves, away from the wall.
Problems with freezing and their solution through adjustment
One of the common problems of old Biryus is the formation of a thick ice crust (“fur coat”) on the back wall or along the entire perimeter of the freezer. This is often confused with a malfunction, but sometimes the cause lies in the incorrect adjustment of the thermostat. If the shutdown temperature is too low, moisture in the air has time to freeze and turn into ice before the compressor stops.
To combat this, you need to slightly increase the shutdown temperature (turn the screw or knob to lower values). It is also important to check the tightness of the door sealing rubber. If warm, humid air enters the chamber, no thermostat will save you from ice, since the system will try to cool the constant flow of heat.
Another nuance is the location of the temperature-sensitive element. In some models it is simply pressed against the evaporator. If the contact is broken or ice chips have accumulated under the element, the readings will be incorrect. It is necessary to defrost the refrigerator completely (for 10-12 hours), clean the drainage hole and check the fit of the sensor.
Common mistakes when setting it up yourself
Trying to save on calling a technician, users often make mistakes that aggravate the situation. The most common of them is an attempt to “turn up” the thermostat to maximum in order to freeze food faster. In old units, this leads to the evaporator becoming overgrown with ice, thermal conductivity drops, and the compressor runs idle, overheating.
The second mistake is ignoring the ambient temperature (room temperature). In winter, when the apartment is cool (+18°C and below), the old refrigerator may not turn on at all at standard settings, since it “does not have enough” heat to trigger the sensor. In such cases, it is necessary to either warm up the thermostat area, or (as a last resort) slightly adjust the screws.
The third mistake is the use of aggressive liquids to clean the thermostat contacts. Alcohol or solvents can corrode the plastic of internal mechanisms or wash away the special lubricant, causing the contacts to stick. To clean contacts, it is better to use a special spray for electrical contacts or a regular eraser.
Is it possible to replace an old thermostat with a new one with a different marking?
Yes, replacement is often possible. For example, thermostats T-133 are interchangeable with TAM-133 i K-59 (with re-soldering of contacts or adaptation of the housing). The main thing is that the length of the capillary tube matches (it should be no shorter than the original, the excess can be carefully rolled up) and the temperature range. For single-chamber models, thermostats with a range from -12 to -24 degrees are suitable.
Why does the Biryusa refrigerator not turn off after adjustment?
If, after turning the knob towards the minimum, the compressor continues to work, this may indicate a freon leak. The thermostat “sees” that the temperature has not reached the threshold and does not give a command to stop. Also, the reason may be a loose fit of the door or a malfunction of the thermostat itself (contacts are stuck).
How do you understand that the thermostat is faulty and needs to be changed?
Symptoms of a malfunction: the refrigerator does not turn on at all (if the light bulb and socket are working), or it turns on and does not turn off for days, even at minimum. Another sign may be the absence of a characteristic click when turning the handle. In such cases, adjustment is useless - the unit must be replaced.
Does the amount of food affect the temperature setting?
Yes, it does significantly. An empty refrigerator cools down faster, but it also heats up faster when the door is opened. A fully loaded refrigerator (thermal inertia of food) keeps the temperature more stable. After a full load of products, you may need to slightly adjust the thermostat knob towards lower temperatures.
Is it necessary to lubricate the thermostat mechanism?
The thermostat mechanism itself is sealed and does not require lubrication during operation. Lubrication is required only for the moving parts of the door and, sometimes, the rod on which the handle fits if it begins to creak. You cannot climb inside the thermostat housing with lubricant - this will disrupt the operation of the springs.