A modern refrigerator is a complex unit that operates on the principle of cyclic cooling, where each element performs a strictly assigned role. Without precise temperature control, food would spoil and the compressor would run continuously, causing rapid wear and tear. It is for this control that the thermostat is responsible, which is the “brain center” of the cooling system.
Many users perceive this unit as a simple knob or button, but in fact it is a measuring device that analyzes the state inside the chambers in real time. Thermoregulator closes and opens the electrical circuit, giving the command to the motor to start or stop. Understanding its operation will help you avoid unnecessary expenses on repairs and maintain the freshness of products.
In this material we will analyze in detail the physical principle of the device, types of thermostats and symptoms of their failure. You will learn why capillary tube is so important for the accuracy of readings and how to distinguish a sensor failure from a compressor malfunction.
The basic principle of operation of a temperature relay
The fundamental task of a thermostat is to maintain a given temperature by compressor operation control. Inside the device there is a sensitive element that responds to changes in the temperature of the environment. When the indicators reach the lower limit, the contacts open and power to the engine stops.
When the air inside the chamber is heated to a certain upper threshold, the reverse process occurs: the contacts close and the compressor starts again. This cycle provides a stable microclimate necessary for food preservation. Older models often use mechanical devices with a a bellowsfilled with refrigerant.
Electronic analogues installed in modern ones Smart refrigeratorsuse thermistors (resistors that change resistance depending on temperature). They transmit data to the control board, which decides to start the motor. Mechanical devices are considered more reliable in conditions of voltage fluctuations, while electronic ones provide high accuracy.
⚠️ Attention: In mechanical thermostats, sensitivity depends on the tightness of the capillary tube to the evaporator. If the tube is displaced or damaged, the readings will be incorrect.
The difference between the on and off temperatures is called hysteresis. The ideal hysteresis for a household refrigerator is 2-3 degrees Celsius, which prevents the motor from turning on too often, but does not allow the food to defrost. Too large a temperature spread can lead to damage to the contents of the chambers.
Design features and types of sensors
The thermostat design may vary significantly depending on the model and year of manufacture of the refrigerator. Mechanical regulators, such as the popular series TAM or K-59, have a plastic body, an adjusting screw and a long sealed tube. At the end of the tube there is a sealed flask filled with freon or other gas.
Electronic sensors are a small element with two wires that connects directly to the control board. They are compact and do not require complex mechanical adjustments, but are sensitive to power surges in the network. To check them, a special tester or multimeter is required.
- 🔧 Mechanical: They work on the compression/expansion of gas in a bellows, control contacts directly, do not require external power.
- 💻 Electronic: Change electrical resistance, transmit a signal to the processor, allow you to accurately set the temperature down to a degree.
- 🌡️ Pneumatic: A less common type, where the air pressure in the tube is transmitted to a membrane that opens the contacts.
It is important to understand that replacing one type with another is possible only with a complete redesign of the refrigerator control system. If you had a mechanical regulator, installing an electronic one will require intervention in the compressor power circuit. Universal solutions There is no such thing here.
Is it possible to repair an old thermostat?
Independent repair of mechanical thermostats is practically impossible and inappropriate. Violation of the tightness of the bellows or capillary tube leads to leakage of the working fluid, and the device stops responding to temperature. It’s easier and cheaper to buy a new analogue, selecting it according to markings or fitting dimensions.
Symptoms of a malfunctioning thermostat
You can determine that the “enemy” lies in the thermostat by the characteristic signs. Most often, the refrigerator begins to behave inappropriately: it either freezes too much, turning vegetables into ice, or stops cooling altogether. In this case, the compressor may hum continuously or be silent.
If you notice that the products in the main chamber have begun to deteriorate faster than usual, and there is no frost on the walls (or, conversely, a “fur coat” has formed), you should check the regulator. Also an alarm bell is the absence of a click when turning the temperature setting knob.
Frequent turning on and off of the motor (clocking) may also indicate sticking of the contacts inside the relay or loss of sensitivity of the sensitive element. In electronic models, an error code associated with the temperature sensor may light up on the display.
- ❄️ Continuous operation: The compressor does not turn off, there is excess cold in the chamber, ice is freezing.
- 🔥 No cold: The motor does not start, the chamber is warm, there is light, but there is no cooling.
- ⚡ Short cycle: The unit turns on for 1-2 minutes and turns off without having time to reach the temperature.
Diagnostics and performance check
Before buying a new part, you need to make sure in its malfunction. The easiest way for a mechanical thermostat is to visually inspect and “test” the contacts with a multimeter. To do this, the refrigerator is disconnected from the network, the regulator handle and the protective casing are removed.
Next, you need to remove the thermostat by disconnecting the capillary tube from the evaporator. Contacts are checked in two states: at room temperature (should ring) and when cooled (should not ring). To check for cooling, place the sensitive flask in a container with ice water.
Sequence of testing with a multimeter:1. Set the resistance measurement mode (Ohm).
2. Connect the probes to the thermostat terminals.
3. At room temperature, the device should show “0” or a close value.
4. Cool the flask with ice - the resistance should become infinite (break).
Electronic sensors are tested by measuring their resistance at different temperatures and comparing the readings with a table of ratings for a specific model. A deviation from the norm of even 10-15% indicates the need for replacement.
⚠️ Attention: When working with electronics, be sure to disconnect the refrigerator from the power supply. A short circuit can damage the control board, the repair of which will cost much more than replacing the thermostat.
The process of replacing the thermostat
Replacing the thermostat is a procedure that can be done with your own hands if you have basic tools. The main thing is to act carefully so as not to damage the capillary tube of the new regulator, since it is filled with gas under pressure. Any microcrack will make the part inoperative.
First, the old element is dismantled. It is important to remember or photograph the wiring diagram. The new thermostat is installed in the reverse order. The capillary tube must be carefully inserted into its normal place and secured so that it fits tightly to the surface of the evaporator.
☑️ Algorithm for replacing the thermostat
After installation, you need to adjust the temperature. Mechanical regulators often require adjustment with a screw inside the housing to achieve the correct hysteresis. If the refrigerator starts to freeze slightly or too much, recalibration will be required.
Comparison of mechanical and electronic systems
Choice between