The refrigerator stopped freezing or, on the contrary, turned the food into ice? In 90% of cases, the culprit for such changes is the thermostat, which ceases to correctly read the temperature inside the chambers. Understanding how this unit should work will help you quickly diagnose a breakdown without calling a technician and save significant money on repairs.
The principle of operation is based on the simple physical law of expansion and compression of substances. Inside the device body there is a sensitive element filled with gas or liquid, which reacts to the slightest climate changes in the freezer compartment. When you realize contact closure mechanismit will become easier for you to understand why the compressor hums without a break or is silent for days.
Modern models may use electronic sensors, but classical mechanics still dominate in most household appliances. We will analyze in detail what is happening inside the system, how to set Thermostat TAM 133 or its analogues, and when immediate replacement of the element is required.
The principle of operation and design of the thermostat
The basis of any mechanical regulator is a sealed bellows tube filled with freon or chloroform. This sensitive element is placed directly in the evaporator area. As the temperature drops, the gas pressure inside the tube drops, which causes the bellows to compress and open the electrical circuit, stopping the compressor.
When the temperature in the chamber begins to rise, the gas expands, the pressure in the bellows increases, and a click occurs. This sound indicates that the contacts are closedand the motor-compressor has received power to start a new cooling cycle. It is important to understand that adjusting the knob on the control panel only changes the tension force of the spring, setting the response threshold.
Electronic analogues work differently: there is no gas and bellows. Measurements are made by a thermistor, the resistance of which varies depending on the heating. The signal is transmitted to control module, which programmatically decides when to turn on the unit. However, even in such systems the principle remains the same - maintaining a given range.
Do not forget that the sensitive tube must fit tightly to the surface of the evaporator. If the fastening is loose, the sensor will read the temperature of the air, not the chamber, which will lead to incorrect operation of the entire system.
⚠️ Attention: When replacing the thermostat, it is strictly forbidden to bend the sensitive tube at an acute angle or apply excessive force to it, as this may break the tightness of the system.
Normal temperature operating conditions
For stable storage of products, it is necessary that the thermostat maintains the temperature in the main compartment in the range from +2 to +6 degrees Celsius. In the freezer, this indicator should drop to -18 degrees or lower. If your device is operating in normal mode, the compressor should turn on and off cyclically.
The duration of the cycle depends on many factors: chamber load, room temperature, frequency of door opening. The normal mode is when the refrigerator runs for about 10-15 minutes and then rests for 20-30 minutes. However, in extreme heat or when fully loaded with warm products, the operating time may increase.
There is the concept of “temperature differential”. This is the difference between the moment the compressor turns on and off. Usually it is about 2-4 degrees. If this parameter is too high, the products may have time to thaw or, conversely, freeze more than necessary.
Below is a table showing the dependence of the position of the regulator on the expected temperature inside the chamber:
| Position of the regulator | Temperature in the chamber (°C) | Compressor operating mode | Recommendation |
|---|---|---|---|
| Minimum (1) | +6..+8 | Rare activations | For storing vegetables |
| Medium (3-4) | +3..+5 | Normal cycle | Daily mode |
| Maximum (6-7) | 0..+2 | Frequent switching on | With heavy load |
| Super Freeze | Below -18 | Continuous operation | Only for quick freezing |
Symptoms of a thermostat malfunction
You can determine that The thermostat has failedby a number of indirect signs that appear long before the refrigerator completely stops. The most obvious symptom is continuous operation of the compressor without rest periods. In this case, the sensor simply does not open the circuit, “not seeing” the low temperature achieved.
The opposite situation is also possible: the refrigerator is silent and does not start, although it is warm inside. This indicates that the contacts have oxidized or are stuck open. Sometimes a light tap on the regulator handle helps, but this is only a temporary measure before replacement.
Another alarming signal is the appearance of large icicles or a “coat” of frost on the back wall, even if you did not turn on the fast freezing mode. This means that the shutdown occurs too late, and the moisture has time to crystallize.
It is worth paying attention to the following signs:
- 🧊 Products in the main chamber freeze, although the regulator is set to minimum.
- 🔊 The compressor makes a clicking sound, tries to start, but immediately stalls (problem with the contact group).
- 🌡️ The temperature in different corners of the chamber is very different from the set one.
- 🔌 The device turns on only after defrosting for 10-12 hours.
⚠️ Attention: If the refrigerator stops turning on after a power surge, first turn, check the integrity of the thermostat contacts before sinning on a burnt-out motor.
Diagnostics and performance testing
Before buying a new part, you need to make sure that it is faulty. For diagnostics, you will need a multimeter set to resistance measurement mode (Ohms). The first step is to turn off the power to the refrigerator and gain access to the thermostat, which is usually located under a plastic cover inside the chamber or outside, near the compressor.
Carefully remove the handles and decorative panels. Disconnect the wires from the sensor terminals. In normal condition (at room temperature), the contacts should be closed, and the device will show zero or a value close to it. If the multimeter shows infinity, the circuit is broken.
For a more accurate test, you can place the sensitive tube in a container with water and ice. When cooled to a certain temperature (depending on the marking), a click should be heard and the resistance on the multimeter will change to infinity. If this does not happen, the part requires replacement.
☑️ Thermostat diagnostics
For example, in some models Indesit or Ariston sensors with three contacts are used, where the third is responsible for the compressor operation indicator lamp. By mixing up the wires, you can disrupt the operation of the indicator light.
Replacing and adjusting a new sensor
The process of replacing a mechanical thermostat does not require specialized tools other than a screwdriver and pliers. The main thing is to choose an analogue with identical parameters, especially the length of the capillary tube and the temperature range of operation. An incorrectly selected part will lead to incorrect operation.
After installing a new element, adjustments must be made. On the body of many thermostats there are special adjustment screws, closed with a seal. Rotating one of them changes the temperature range, and the other changes the differential value. Without experience, it is better not to touch the factory settings, but to use only the external handle.
After assembling and turning on the refrigerator, let it work for several hours without loading food. Measure the temperature with a regular thermometer placed in a glass of water on the middle shelf. If the indicators do not correspond to the desired ones, you can tighten the knob a little.
What will happen if you install a thermostat with a different marking?
If you install a sensor with a narrower range, the refrigerator will turn on too often, which will lead to wear on the compressor. If the range is wider, the products may spoil due to insufficient cold.
It should be taken into account that in two-compressor systems, replacement is carried out separately for each chamber. An error when connecting wires to the wrong terminals can lead to a short circuit or failure of the control board.
⚠️ Attention: The technical characteristics of thermostats may vary even within the same refrigerator model. Always check the markings on the old part with the new one before purchasing.
Features of electronic control systems
In modern models with a system No Frost and electronic control, the role of a mechanical thermostat is performed by temperature sensors (thermistors). They are resistors that change their resistance depending on heat. Checking such elements is carried out exclusively with a multimeter.
Electronics allows you to set the temperature with an accuracy of a degree, but makes the system more sensitive to voltage changes in the network. Often, a breakdown of the “thermostat” in such refrigerators is actually an error in the software or a malfunction of the control module.
Diagnostics of electronic systems often requires entering the service mode, where you can see the current sensor readings in real time. This greatly simplifies troubleshooting, since there is no need to disassemble half of the unit.
If you notice that the refrigerator is operating unstable after a thunderstorm or power surge, first check the electronic components of the temperature control system.
Frequently asked questions (FAQ)
Is it possible to temporarily short-circuit the thermostat so that the refrigerator did it work?
Technically, you can connect the wires directly, and the compressor will start. However, in this mode the refrigerator will run continuously until you turn it off manually. This will result in deep freezing of food and possible freezing of the evaporator. Use this method only for short-term diagnostics.
Why doesn’t the new thermostat click?
The absence of a characteristic click may indicate a defective new part, or that the temperature has not yet reached the response threshold. It is also possible that the sensitive tube is poorly pressed to the evaporator and does not feel real cold.
How often should you change the thermostat?
The service life of a high-quality mechanical thermostat is 5-7 years or more. However, with frequent power surges or mechanical damage (shocks during washing, bending of the tube), it may fail earlier. Planned replacement is not required, only after a breakdown.
Does the length of the capillary tube affect the operation?
Yes, this is a critical parameter. If the tube is too short, its end will not reach the desired zone of the evaporator, and the sensor will show the wrong temperature. If it is too long, it may bend or be damaged during installation.