The refrigerator has stopped freezing or, on the contrary, turned the food into ice? In most cases, the culprit of these troubles is the thermostat. This small device controls the operation of the compressor, turning it on and off depending on the temperature inside the chambers. If the mechanism fails, the refrigerator either works continuously, trying to achieve unattainable cold, or remains silent, allowing food to spoil.
Before calling a technician and paying for diagnostics, you should try to figure it out yourself. Checking the thermostat is one of the most accessible procedures in the repair of household appliances, which does not require deep engineering knowledge. All you need is a basic set of tools and attentiveness. In this article we will look in detail at how to identify a malfunction, what tools to use and when replacing a part is inevitable.
Do not rush to write off this unit. Often the problem lies precisely in contact group or a violation of the tightness of the bellows. Understanding the operating principle will allow you to save a significant amount and extend the life of your equipment. Let's start with the theory so that you have a clear idea of what exactly we will be looking for.
Principle of operation and main symptoms of malfunction
The thermostat is a relay that opens or closes an electrical circuit. Inside the device there is a bellows (corrugated tube) filled with a refrigerant that is sensitive to temperature changes. When the air in the chamber heats up, the gas expands, the pressure in the bellows increases, and the contacts close - the compressor starts. When the desired cold is achieved, the process proceeds in the reverse order.
If this mechanism fails, you will notice characteristic changes in the operation of the unit. Most often, users are faced with the fact that the refrigerator hums incessantly, trying to catch up with the temperature, or is silent for days, ignoring defrosting. Also, an alarm bell may be the incorrect operation of the indicators or the complete absence of a click when turning the handle.
Pay attention to the following symptoms that indicate the need for checking:
- 🧊 The compressor works continuously, without turning off even at night, and the food in the freezer is covered with a thick crust of ice.
- 🔌 The refrigerator does not turn on at all, although the light inside is on and the network is working.
- 🌡️ The temperature in the chambers does not correspond to the set values, despite the proper operation of the fan.
- 🔊 You do not hear a characteristic click when turning the regulator knob or when tapping on the case thermostat.
It is important to understand that similar symptoms can also appear if there is a freon leak or a faulty start relay. However, it is thermostat that is the first element that should be checked, since it costs less than other components and more often fails due to changes in temperature and humidity.
Preparation for diagnostics: tools and safety
Before you begin disassembly, you must ensure safe working conditions. Remember that the refrigerator is connected to a 220 Volt electrical network. Any manipulations with wiring and contacts should be carried out only with the device completely de-energized. This is an axiom, ignoring which can lead to electric shock or short circuit.
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be a multimeter (tester), which will allow you to ring the circuit for resistance or an open circuit. If you don’t have a multimeter, you can use a simple “control” - a light bulb with two wires, but a digital device will give a more accurate result.
Also prepare the following items:
- 🔧 Screwdrivers (Phillips and flathead) for removing panels and dismantling the thermostat.
- 🧤 Dielectric gloves for additional hand protection.
- 📸 Smartphone with a camera to take a photo of the wire connection diagram before disconnecting.
- 🧼 Dry rags to clean contacts from oxides and dust.
Pay special attention to access to the thermostat. In different models of refrigerators (Indesit, Bosch, LG, Atlant) it can be located in different places: inside the refrigerator compartment, under the top cover or in the control unit. Study the instructions for your model in advance or find a diagram on the Internet so as not to break the plastic latches.
⚠️ Attention: Never try to check the thermostat while the power cord is plugged into the outlet. Even if you use dielectric tools, the risk of an accidental short to the housing or adjacent wires remains high.
Visual inspection and search for the thermostat
The first stage of diagnosis is the search for the device itself. In older models of mechanically controlled refrigerators, the control knob is usually located inside the refrigerator compartment, on the side wall or on the ceiling. In modern models with a No Frost system, the thermostat is often hidden behind a plastic panel or integrated into the electronic control unit.
If the handle is inside, carefully remove the plastic lever (sometimes it is simply tensioned, sometimes it is held on by a screw). Below it you will see a hole leading to the thermostat housing. To get to the contacts, you may need to remove the top cover of the refrigerator or dismantle the ceiling lamp if the thermostat is located next to it.
During a visual inspection, pay attention to the condition capillary tube. This is a thin copper or aluminum tube that goes deep into the housing or is attached to the evaporator. It should not have creases, cracks or signs of corrosion. Damage to the tube leads to leakage of the filler gas, causing the bellows to stop responding to temperature changes.
Where is the thermostat located in two-compressor refrigerators?
In refrigerators with two compressors (separate for the freezer and refrigerator compartment) There are also two thermostats. Usually one is located in the refrigerator compartment, and the second is in the freezer, often hidden behind the back wall or evaporator cover panel.
Inspect the contacts for carbon deposits. If you see black spots or oxidation on the terminals, this may be the cause of poor contact. Sometimes just cleaning them with fine sandpaper or a file is enough to get the device working again. However, if the plastic has melted, replacement is necessary in any case.
Checking the thermostat with a multimeter
The most reliable way to check is to use a multimeter in resistance (Ohm) or continuity measurement mode. To do this, the thermostat must be removed from its seat, having previously photographed the connection of the wires. Typically, 2, 3 or 4 wires are suitable for the device, depending on the model.
The test process is as follows:
- Set the multimeter to the dialing mode.
- Connect the probes to the input and output contacts of the thermostat.
- At room temperature the contacts should be closed (the device will beep or show 0 Ohm) if it is a regular thermostat.
- Place the sensitive part of the thermostat (bellows) in a container with cold water (about 0...+5°C) or press it against ice.
- After a few minutes the contacts should open (the resistance will go to infinity).
If during cooling there is no click and the instrument readings do not change, it means the mechanism is stuck or the gas in the bellows has evaporated. It is also worth checking the contacts for ground (housing). We place one probe on the contact, the second on the metal body of the thermostat. The device should not show resistance. If the arrow moves, an insulation breakdown has occurred, the device is dangerous for use.
☑️ Algorithm for checking with a multimeter
In some models, thermostats have three contacts: one common, one for the compressor and one for the light bulb or fan In this case, it is important not to confuse the pairs. Usually the markings are on the body, but they can be erased. The correspondence table below will help here.
| Thermostat type | Number of contacts | Heating behavior | Cooling behavior |
|---|---|---|---|
| Single contact (mechanical) | 2 | Open the circuit (stop compressor) | Close the circuit (start compressor) |
| With defrost contact | 3 | Open the compressor, close the defrost | Closes the compressor, opens the defrost |
| Electronic (sensor) | 2 (sometimes 3) | Changes the resistance | Changes the resistance |
Diagnostics without a multimeter: method of elimination
What to do if you don’t have a tester at hand? There is a "short circuit" test method that allows you to determine whether the thermostat is alive without measuring instruments. This method is less accurate, but in an emergency it helps to understand whether it is worth buying a new part.
The essence of the method is to directly connect the wires coming from the network to the compressor, bypassing the thermostat. If after connecting the wires the compressor starts, it means that the motor itself and the start relay are working, and the problem is most likely in the regulator. However, this method requires caution.
Procedure:
- ⚡ Unplug the refrigerator.
- 🔌 Find the wires going to the thermostat (usually they differ in color or marking).
- 🔗 Connect them between themselves using an insulating terminal or twist (after stripping the ends).
- 🔌 Plug in the refrigerator.
If the compressor started working and began to freeze, it means that the thermostat does not really close the circuit. In this case, it must be replaced. If the compressor hums, but does not start, or is silent, the problem may be in the start relay or the motor itself.
⚠️ Attention: Do not leave the refrigerator to work with the wires closed, bypassing the thermostat, for a long time! The compressor will run continuously, which will lead to freezing of the evaporator, overheating of the engine and possible defrosting of food due to violation of cycling.
This method is good for quick diagnostics, but it does not test the ability of the thermostat to open the circuit when the desired temperature is reached. Therefore, after such a check, it is still recommended to install a new part for full operation.
Resistance table and technical parameters
For those who want to conduct more in-depth diagnostics, it is useful to know the typical resistance values for various types of thermostats. Although mechanical relays should read either 0 or infinity, electronic sensors (thermistors) work differently, changing their resistance depending on temperature.
The following is a reference table for common temperature sensor models that are often confused with mechanical thermostats in modern refrigerators:
| Sensor Model | Temperature, °C | Resistance, kOhm | Tolerance |
|---|---|---|---|
| K59 (mechanical) | +20 | 0 (closed) | - |
| K59 (mechanical) | -20 | ∞ (open) | - |
| LG sensor (6kOhm) | +25 | 6.0 | ±5% |
| LG sensor (6kOhm) | 0 | 16.5 | ±10% |
If you are checking an electronic sensor, you will need The resistance table is specific to your refrigerator model, since there are no universal values. A deviation from the norm of more than 10-15% indicates a malfunction of the element.
When replacing a mechanical thermostat with an analogue, it is important to pay attention not only to the mounting dimensions, but also to the length of the capillary tube. If the new tube is shorter, the refrigerator may incorrectly read the temperature, which will lead to frequent switching on or, conversely, to rare operating cycles.
Frequently asked questions and final recommendations
Refrigerator repair is a process that requires accuracy. We have discussed the main inspection methods, from visual inspection to instrumental diagnostics. To summarize, I would like to note that the thermostat is a consumable item. Sooner or later, its contacts burn out and the gas evaporates, so replacement is a normal part of operating the equipment.
Do not try to repair the thermostat housing itself or solder the bellows. This device cannot be repaired at home. Attempts to adjust the screws inside the case without special equipment and knowledge most often lead to complete failure of the unit.
Is it possible to temporarily do without replacing the thermostat?
Technically, you can use the method of shorting the wires to bypass the regulator by connecting the refrigerator via a timer or manually turning it on for several hours a day. However, this is inconvenient and risky: you may forget to turn off the device, and the food will spoil, or the compressor will burn out from overheating. This solution is only for a couple of days before the technician arrives.
Why doesn’t the new thermostat click?
Some modern thermostats operate almost silently. The absence of a loud click does not always mean a defect. Check the operation with a multimeter: if the contacts open and close as the temperature changes, the device is working properly, even if you do not hear a sound.
How often should you change the thermostat?
The service life of the thermostat is on average 5-7 years of active use. Frequent power surges and temperature fluctuations in the chamber (for example, when loading hot products) can shorten this period. Preventive replacement is not required, change only when symptoms of a malfunction appear.
Does the type of freon affect the choice of thermostat?
Yes, indirectly. Thermostats are calibrated for specific temperature ranges, which depend on the type of refrigerant and the design of the refrigerator. When purchasing a new part, be sure to tell the seller the model of your refrigerator or show the markings of the old thermostat.
If the problem does not go away after replacing the thermostat, it may be a freon leak or a compressor malfunction. In this case, you cannot do without professional diagnostics and specialized equipment. But in 80% of cases, it is the replacement of the thermostat that brings the refrigerator back to life.