A modern refrigerator is a complex system where each element is responsible for maintaining a stable temperature necessary for the preservation of food. In this circuit, the key role is played by the sensor, which “makes the decision” to turn the compressor on or off. It is this mechanism, often called a thermostat switch, that provides that rhythmic hum and subsequent silence familiar to every owner of household appliances.
If you notice that the unit has stopped turning off, is working without interruptions, or, conversely, does not start at all, the problem often lies in this particular unit. Understanding how it works thermostatwill allow you to avoid an expensive call to a technician for a simple diagnosis. In this article, we will analyze in detail the principle of operation of the device, its design features and methods of troubleshooting.
Ignoring the symptoms of failure of this element can lead to damage to products or failure of more expensive components, such as a compressor. Therefore, timely identification of the problem is the key to the long service life of your equipment. Next, we will move on to technical details and practical advice.
The principle of operation and design of the thermostat
The thermostat, or thermostat, is the main control element in a refrigerator with a mechanical control system. Its task is simple, but critical: to close or open an electrical circuit depending on the temperature inside the refrigerator compartment. Inside the device there is a sensitive tube filled with gas or liquid, which responds to thermal expansion.
When the temperature in the chamber rises above the set value, the gas in the tube expands, presses on the membrane and closes the contacts. At this moment, compressorstarts, starting the cooling cycle. As soon as the temperature drops to a predetermined minimum, the pressure drops, the contacts open and the motor stops. This cycle is repeated endlessly as long as the refrigerator is plugged in.
In some models, especially modern ones, the mechanical thermostat can be replaced by an electronic sensor, but the principle remains similar. The switch in mechanical models often has a scale with numbers from 1 to 7, where 1 is the warmest setting and 7 is the coldest. It is important to understand that these numbers do not indicate degrees Celsius, but only conditional values of the intensity of work.
⚠️ Attention: In refrigerators with a system No Frost the thermostat can control not only the temperature in the chamber, but also the operation of the defrost system. Incorrect setting or breakdown here can lead to freezing of the evaporator and disruption of air circulation.
How does the capillary tube work?
The capillary tube of the thermostat is hermetically sealed and fixed to the evaporator. When the temperature changes, the pressure inside the tube changes, which mechanically affects the switch contacts. If the tube is damaged or displaced, the temperature readings will be incorrect.
Main signs of a faulty switch
You can determine that the thermostat switch is faulty by characteristic changes in the operation of the refrigerator. The most obvious sign is the continuous operation of the compressor. If the unit hums constantly, without pausing to rest, and at the same time there is severe freezing inside the chamber or food begins to freeze, this is a direct signal that the contacts are stuck in the “on” position.
The opposite situation also indicates a problem: the refrigerator is silent, the light inside is on, but there is no cold. In this case, the thermostat contacts could oxidize or burn out, breaking the compressor power circuit. Even if you turn the control knob, there may not be a click, which is usually heard when switching modes.
- 🔌 The compressor does not start even when you turn the control knob to maximum.
- ❄️ The refrigerator compartment is too warm or, conversely, all the products are covered with frost.
- 🔊 Absence of a characteristic click when adjusting the temperature.
- 📉 Frequent switching on and off of the motor at short intervals.
Sometimes the malfunction does not appear immediately, but gradually. You may notice that food begins to spoil faster, or the ice in the freezer begins to melt and refreeze, forming grains. This indicates that thermostat is not working correctly, transmitting incorrect temperature data.
Instructions for checking the thermostat with a multimeter
For accurate diagnostics, you will need a multimeter set to the “continuity” mode or resistance measurement. Before starting any work, you must completely turn off the power to the refrigerator by removing the plug from the socket. This safety requirement is mandatory, since working with live electrical wiring is life-threatening.
First you need to gain access to the thermostat. In most models, it is located inside the refrigerator compartment, under the plastic panel where the temperature control knob is installed. Carefully remove the handle and unscrew the screws securing the housing. Disconnect the wires from the thermostat contacts, having previously memorized or photographed their location.
Attach the multimeter probes to the thermostat contacts. If the device shows “0” or makes a beep, it means the circuit is shorted. This is normal at room temperature. Now place the sensitive tube of the thermostat (or the device itself, if it is dismantled) in a cold environment, for example, in the freezer for 10-15 minutes.
☑️ Preparation for diagnostics
After cooling, repeat the check with a multimeter. If the thermostat is working properly, the circuit should break and the meter will show infinite resistance (or silence). If the contacts remain closed even in the cold, it means switching mechanism it is broken and requires replacement.
⚠️ Attention: If you are not confident in your skills in working with electrical appliances, it is better not to take risks. Incorrect assembly or short circuit of the wires can lead to a short circuit and failure of the compressor.
The process of replacing a thermostat with your own hands
Replacing a thermostat is a procedure that can be performed at home if you have basic skills and a new working element. The main rule: the new thermostat must be completely identical to the old one. Pay attention to the length of the capillary tube, the number of contacts and the method of attachment.
Dismantling the old device is carried out in the reverse order. Carefully pull the sensing tube out of its seat on the evaporator. Be careful: the tube is very thin and easily damaged. Install the new thermostat, fixing the tube in the same position as the previous one. Any offset may lead to incorrect temperature readings.
Connect the wires according to the diagram or photograph you made earlier. Securely fasten the device body and install the decorative panel. After assembly, plug in the refrigerator. For the first few hours, it can work in enhanced mode, gaining temperature, so do not load the chamber with products right away.
| Working stage | Necessary actions | Important nuances |
|---|---|---|
| Dismantling | Removing the handle, unscrewing the screws, disconnecting the wires | Take a photo of the wire connection diagram |
| Removing the tube | Carefully pulling it out of the evaporator channel | Do not pull the tube itself, only the body |
| Installing a new | Mounting the housing and fixing the tube | The tube must fit tightly to the evaporator |
| Checking | Switching on and monitoring operation | Monitor the cyclic switching on of the compressor |
Adjusting and setting the temperature mode
After installing a new switch or during operation, it may be necessary to adjust the temperature mode. The regulator knob usually has divisions, but they are not tied to specific degrees. The optimal position is when the refrigerator operates cyclically, and the temperature in the main chamber is about +4...+5°C.
If you notice that the food in the back of the chamber begins to freeze, you should turn the knob towards lower values (for example, from 4 to 3). Conversely, if the refrigerator is warm, increase the value. Remember that changing settings does not take effect instantly, but after several operating cycles.
It is important to take into account external factors. In the summer, when the room is hot, the thermostat has to work harder. In winter, if the refrigerator is in an unheated room, the mechanical thermostat may not turn on the compressor at all, since it “seems” to it that it is already cold enough inside. For such cases, there are special models with the function of operating at low ambient temperatures.
Frequent errors during maintenance and diagnostics
When trying to repair things on their own, users often make mistakes that make the situation worse. One of the most common is ignoring the condition of door seals. If the door does not close tightly, warm air enters the chamber, and the thermostat, trying to compensate for the loss of cold, forces the compressor to work continuously. In this case, replacing the thermostat will not solve the problem.
Another mistake is incorrect installation of the sensitive tube. If it does not fit snugly against the evaporator or is moved to the side, the temperature reading will be distorted. As a result, the refrigerator will either undercool the food or overfreeze it. Also, you should not try to repair the thermostat itself: it is a sealed unit that cannot be restored.
Do not forget that in modern models with electronic control, the role of a mechanical switch is performed by a temperature sensor. The diagnostic principle here is different: the resistance of the sensor is checked, not the closure of the contacts. An attempt to apply mechanical diagnostic methods to electronics can lead to damage to the control board.
Is it possible to operate a refrigerator with a faulty thermostat?
Short-term operation is possible, but undesirable. If the contacts are “stuck” while on, the compressor will work without stopping, which will lead to its overheating and eventual breakdown, as well as excessive energy consumption. If the contacts are open, the food will simply spoil.
Why does the thermostat click, but the refrigerator does not turn on?
The click means that the switching mechanism has worked, but the current has not gone further. This may indicate a malfunction of the compressor itself, the start relay, or a break in the wiring. Also, the cause may be a burnt contact inside the thermostat, which looks intact from the outside.
How often should the thermostat be changed?
The thermostat does not have a strict expiration date. It is changed only after a breakdown. With careful operation and stable mains voltage, the device can last 10 years or more. Sudden voltage surges are the main enemy of the electrical contacts of the thermostat.
Does defrosting affect the operation of the thermostat?
Regular defrosting is necessary for refrigerators with a drip system, but this does not damage the thermostat itself. However, if you use a hairdryer or hot water to speed up defrosting and direct a stream of hot air directly at the thermostat, this can damage its sensitive element.
What to do if the new thermostat does not fit the length of the tube?
The capillary tube should never be shortened or extended. If the length does not match, you need to look for an analogue model with suitable parameters. An incorrect length will result in the tube either not reaching the evaporator, or in doubt, which will disrupt the operation of the entire system.