The situation when the refrigerator stops freezing or, conversely, turns food into an ice block, always takes you by surprise. In most cases, the culprit for such differences is the thermostat - a small but critical element of the temperature control system. It is he who is responsible for the timely switching on and off of the compressor, maintaining the desired microclimate in the chambers.
If thermostat it fails, the equipment begins to work chaotically: it either hums without interruption, or stands silently for hours. Understanding how this unit works will help you quickly identify the problem and avoid spoiling a large stock of food. We will analyze in detail why this part breaks and how to independently carry out initial diagnostics.
It is important to note that modern models can be equipped with electronic control modules, where the function of a mechanical regulator is performed by thermal sensor. However, the diagnostic principle is largely similar, although the testing methods differ. In this article we will focus on classic mechanical systems, which are most often subject to manual repair.
Mechanical rupture of the bellows tubes are the most common and irreversible cause of failure, requiring a complete replacement of the unit, since the tightness cannot be restored. Attempts to solder the tube or fill it with sealant are, as a rule, doomed to failure due to the specifics of the filler gas.
Before disassembling the unit, you should make sure that the problem lies precisely in the temperature control. Often, users accidentally change the settings or encounter simple freezing of the evaporator, which blocks the operation of the sensor. Let's look at the main symptoms that will indicate a thermostat failure.
⚠️ Attention: Before any diagnostic work, be sure to disconnect the refrigerator from the power supply. Working with live electrical components is deadly.
Main symptoms of a malfunctioning thermostat
The first sign that thermostat is not working correctly is a change in the operating mode of the compressor. If the motor hums almost non-stop, trying to catch up with the temperature, or turns on extremely rarely, allowing the food to defrost, this is a direct signal to check. In a normal cycle, the refrigerator should work approximately 40% of the time and rest 60%.
Another alarming symptom is the complete absence of cold when the engine is running. You hear a hum, but it's warm inside. This may mean that the contacts inside the regulator are “stuck” in the open state, and the command to start the compressor simply does not arrive, although the motor itself is working. It is also worth paying attention to the camera:
- ❄️ A “fur coat” or ice crust has formed on the back wall in the refrigerator compartment.
- 🔊 The compressor works continuously, without resting for more than 2 hours.
- 🌡️ The temperature in the chamber does not correspond to the set temperature the value of the regulator knob.
- 💧 The appearance of water under the refrigerator due to frequent defrosting of the evaporator.
In some cases, a breakdown manifests itself in the form of a spontaneous shutdown. The unit freezes food to the point of stone, and then turns off indefinitely. This indicates that bellows tube has lost sensitivity or has shifted, transmitting incorrect data about the temperature inside the chamber.
The design and principle of operation of the thermostat
To understand why it doesn’t work thermostatyou need to imagine its internal structure. A classic mechanical thermostat is a sealed system filled with gas (freon) that responds to temperature changes. The main element here is a bellows (accordion), which contracts when cooled and expands when heated.
Inside the housing there is a group of contacts that open or close under the influence of gas pressure in the bellows. When you turn the adjustment knob, you change the spring tension, setting the force required to open the contacts. In models Indesit or Atlant this assembly often looks like a plastic block with three or four wires.
How does a bellows tube work?
A bellows tube is a thin copper or aluminum capillary tube sealed at one end. It is filled with an inert gas, which changes its pressure when the temperature changes. This gas is in thermodynamic equilibrium with the refrigerant in the system, which allows you to accurately monitor the evaporator temperature.
It is important to consider that different models of refrigerators use different types of thermostats. For example, in two-chamber models, the sensor can monitor the temperature of the evaporator, and in single-chamber models, the air in the chamber. The design contact group may also differ: in some versions there is a third contact to turn on the fan or defrost indicator.
⚠️ Attention: The bellows tube is very thin and fragile. If handled carelessly during diagnostics, it can easily be damaged, which will lead to gas leakage and final failure of the unit.
Why the thermostat breaks: the main reasons
The most common reason for failure is natural wear and tear of mechanical parts. Over time, the spring loses its elasticity, and the contacts burn from constant sparks when switching. This leads to the fact that contact group stops conducting current or, conversely, sticks. The resource of a high-quality thermostat is usually 5-7 years of active operation.
The second factor is a violation of the tightness of the bellows tube. If a microcrack appears in the system, the gas evaporates and the pressure ceases to depend on temperature. As a result, the bellows does not compress, the contacts do not open, and the refrigerator operates non-stop. This often occurs due to metal corrosion or mechanical damage during defrosting.
The third reason is oxidation of contacts. Under conditions of high humidity inside the refrigerator compartment, especially if the wiring insulation is damaged, an oxide film forms on the terminals. It creates high resistance, which causes the signal to pass through intermittently. In models Beko or LG this often happens if water gets on the connectors when washing.
It is also worth mentioning the effect of power surges in the network. Although a thermostat is a mechanical device, the electric arc that occurs when the contacts open under load can melt the plastic or weld the contacts together. Using a surge protector or stabilizer can extend the life of this unit.
- ⏳ Natural wear of the spring and contacts after 5-7 years of service.
- 💨 Depressurization of the bellows tube and leakage of filler gas.
- ⚡ Burning or welding of contacts due to voltage surges.
- 💧 Moisture on the terminal block and oxidation of the connections.
Diagnostics: how to check a thermostat with a multimeter
For accurate diagnostics you will need multimeterconfigured for continuity testing or resistance measurement mode. The first step is to gain access to the thermostat. In most refrigerators it is located inside the chamber (under the plastic adjustment knob) or outside, above the door. Remove the handle and unscrew the fixing screw.
After removing the assembly, disconnect the wires. Usually there are two or three. If there are three wires, then one goes to the light bulb or fan, and the two main ones go to the compressor. We need to check exactly the main circuit. At room temperature, the contacts should be closed (the multimeter beeps). If there is an immediate break, the thermostat is faulty.
☑️ Checking the thermostat with a multimeter
Next we will check the reaction to cold. Place the thermostat sensing part (bellows tube) in the freezer or apply ice to it. After 10-15 minutes, when the temperature drops below zero, the contacts should open and the multimeter should show infinite resistance. If this does not happen - mechanism jammed.
⚠️ Attention: If you are checking a thermostat with three contacts, make sure that you are calling the exact pair that is responsible for the compressor. The third contact can be normally closed or normally open, depending on the operating logic of a particular model.
Table: Comparison of symptoms and causes
For the convenience of systematizing problems, we present a table that will help compare the observed symptoms with the most likely causes. This will allow you to quickly navigate the situation before the technician arrives or begin your own repairs.
| Symptom | Probable cause | Required action |
|---|---|---|
| The refrigerator does not turn on, there is light | Breakage of thermostat contacts | Replacing the thermostat |
| Works without stopping, there is ice in the chamber | Contacts are "stuck" or gas leak | Diagnostics with a multimeter, replacement |
| Frequent on/off | Incorrect calibration or oxidation | Cleaning contacts, adjustment |
| Temperature is not adjustable with the handle | Broken rod or spring inside | Complete replacement of the unit |
As can be seen from the table, most problems are solved by replacing the element. Repairing the internal mechanics of a thermostat at home is practically impossible due to the need to calibrate and evacuate the bellows.
Instructions for replacing the thermostat with your own hands
If the diagnostics confirm the malfunction, we proceed to the replacement. This process requires accuracy, but is not a complex technical operation. The main thing is to act consistently and not damage new components. First, purchase an analogue that fully matches your refrigerator model refrigerator models.
Remove the old thermostat, remembering or photographing the wiring diagram. Place the new assembly in place, securing it with screws. Pay special attention to the installation of the bellows tube: it should fit tightly to the evaporator in the same place where the old one was. Often a special bracket or clamp is used for fixation.
Sequence of actions:1. Turn off the power.
2. Remove the handle and decorative panel.
3. Unscrew the thermostat mount.
4. Remove the tube from the mounting hole.
5. Disconnect the wires (remember the colors!).
6. Install the new thermostat in the reverse order.
7. Check operation.
After assembly, turn on the refrigerator and let it work for 2-3 hours. Check if it rises to temperature and if the compressor turns off. If the operation cycle (restored), then the replacement was successful. Otherwise, it is worth checking the tightness of the tube.
Frequently asked questions (FAQ)
Is it possible to temporarily short-circuit the thermostat to make the refrigerator work?
Yes, you can connect the two main wires (bypassing the thermostat) to the compressor started working directly. However, in this mode the refrigerator will run continuously until you turn it off manually. This is fraught with freezing of food and icing of the evaporator. Use this method only as a temporary measure for defrosting or shipping.
Why doesn't the new thermostat click when the temperature changes?
If you just installed a new one thermostat and it doesn't make a clicking noise, the temperature range may not have been reached yet. It is also worth checking whether the tube is installed correctly. If there are no clicks at all and the refrigerator does not respond, you may have been sold a defective product or a model with other response parameters.
How often do you need to change the thermostat in the refrigerator?
The service life of the thermostat usually coincides with the service life of the refrigerator itself or is 5-10 years No scheduled replacement required. They change it only when obvious signs of a malfunction appear: a violation of the temperature regime or the compressor refuses to turn on/off.
Can a thermostat affect the operation of the No Frost system?
Yes, in systems No Frost the thermostat (or defrost sensor) controls the operation of the heating element and fan. If it is faulty, the evaporator may become overgrown with ice, blocking airflow, or the heating element will heat constantly, overheating the chamber. The principle of checking is similar, but it is important to take into account the specifics of the electrical circuit of a particular model.