Sudden defrosting of food or, conversely, the formation of an ice crust on the back wall often indicates a failure in the temperature control system. In most household models, this process is carried out by thermostat a small device that opens the compressor power circuit when the set temperature is reached. If the refrigerator stops turning off or turns on too rarely, the reason may lie in this sensor.
Before calling a technician, it makes sense to carry out initial diagnostics yourself. This will save time waiting for a specialist and, possibly, money if the problem is solved by replacing an inexpensive part. To correctly assess the condition of the unit, you will need a minimum set of tools and an understanding of the operating principle of a mechanical thermostat.
In this article we will analyze in detail the algorithm of actions that will help determine the operability of the device. You will learn how to interpret multimeter readings and what visual signs you should pay attention to first.
Main signs of a malfunctioning thermostat
The first stage of diagnosis is always monitoring the operation of the unit. Thermostat is a mechanical or electronic switch, and its breakdown rarely occurs without a trace. There are a number of characteristic symptoms that most likely indicate a problem in the temperature control circuit.
If the compressor runs continuously without turning off for hours, and the temperature inside the chambers drops below normal (food freezes), this is a classic sign of contacts sticking in the “on” position. In the opposite situation, when the engine does not start at all, but it becomes warm inside, you can suspect an open circuit or loss of sensitivity of the bellows tube.
- 🧊 The compressor hums constantly, without going into standby mode, even with the minimum settings of the regulator knob.
- 🔌 The refrigerator does not turn on at all, although the light inside is on and there is voltage in the network.
- ❄️ A “fur coat” or ice forms on the back wall of the main chamber, although this has not been observed before.
It is also important to listen to the characteristic clicks. A working device makes a distinct sound when the contacts open. If you turn the adjustment knob and there is no characteristic click, this may indicate mechanical destruction of the internal components.
⚠️ Attention: If the compressor operates continuously for more than 12 hours, this may lead to overheating of the motor and its failure. If such a symptom is detected, it is recommended to temporarily disconnect the device from the network until diagnostics are carried out.
Preparation for diagnostics: tools and safety
To carry out a quality test, you will need a basic home repair kit. The main tool will be multimeter (tester), which allows you to measure the resistance of the circuit. Without it, the diagnosis will be only approximate, based on indirect signs.
Before starting any work, you must completely turn off the power to the refrigerator. Unplug the plug from the socket. Even if you plan to check only the mechanical part, accidental phase contact with the housing or tools can lead to unpleasant consequences. Also prepare a screwdriver for removing the protective covers.
☑️ Preparing to check the thermostat
In some models, access to the thermostat may be difficult. In old Soviet refrigerators it is often located inside the chamber, in new ones it is behind a plastic panel or in the engine compartment. Assess in advance whether you need to defrost the unit to access the unit. Note: The design and location of thermostats may vary depending on the brand and year of manufacture of the model. Always check the technical documentation for your specific model before disassembling.
ℹ️ Note: Thermostat design and location may vary depending on brand and model year Indesit, Atlant or Bosch. Always check the technical documentation for your specific model before disassembling.
Removing the thermostat for inspection
To check thermostat directly, it must be removed from the housing. In refrigerators with a weeping defrost system, the regulator is usually located inside the refrigerator compartment. It is hidden under a plastic cover or located in the corner of the top.
Carefully remove the temperature control knob. There may be a mounting screw underneath. Unscrew it and remove the decorative panel. You will see a metal flask with a long capillary tube that goes deep into the body or is attached to the evaporator.
It is important not to damage the capillary tube when removing it. There is a refrigerant inside it that reacts to changes in temperature. If the tube bursts or becomes deformed, the thermostat will have to be thrown away as it cannot be repaired. Carefully disconnect the wires, first remembering or photographing their connection diagram.
- 📸 Take a photo of connecting the wires before disconnecting, so as not to confuse the contacts during assembly.
- 🔧 Use insulated tools to work with electrical contacts.
- 🧤 Handle with care capillary tube, avoiding sharp bends.
After removing the device, inspect its body. There should be no cracks, traces of burning or melting of the plastic. The presence of black carbon deposits on the contacts indicates that sparking has occurred in the device, which is a sure sign of a malfunction.
Checking the thermostat with a multimeter
The most accurate diagnostic method is checking the electrical resistance using multimeter. Switch the device to resistance (Ohm) or continuity measurement mode. This will allow you to determine whether the circuit closes when the temperature changes.
Connect the tester probes to the thermostat contacts. In the initial state (at room temperature), the contacts should be closed, and the device will show zero or a value close to it. If a unit or an infinity symbol is lit on the screen, the circuit is broken and the thermostat is faulty.
Nuances of checking three-contact thermostats
Modern models often use thermostats with three contacts. The third contact is usually responsible for indicating the emergency temperature or operating the fan. When testing the main pair of contacts (usually 3 and 4), the behavior should be similar to two-contact models. The third contact may not ring at room temperature - this is normal; it closes only with strong heating or cooling, depending on the operating logic.
For a complete check, you need to cool the sensitive part of the device. Place the capillary tube (about 5 cm from the end) in a container of water and ice or simply apply it to the frozen product for 2-3 minutes. After cooling, the resistance should change (open) and the multimeter will indicate an open circuit. If this does not happen, it means bellows mechanism does not respond to cold.
Restore the device to room temperature. The contacts should close again with a characteristic click. Lack of response to heating also indicates a breakdown.
Comparative table of multimeter readings
For ease of interpretation of measurement results, use the table below. It will help to quickly classify the state of the element being tested.
| Contact state | Multimeter readings | Cooling action | Verdict |
|---|---|---|---|
| Closed (room t°) | 0 - 5 Ohm | Open (infinity) | Good |
| Open (room t°) | 1 (infinity) | No change | Faulty (break) |
| Closed (room t°) | 0 - 5 Ohm | Remain closed | Faulty (stuck) |
| Short/Open | Unstable numbers | Chaotic changes | Bad contact/Oxide |
Please note that in some electronic models, instead of a classic thermostat, thermal sensor (thermistor). It is checked differently: it is not just a short circuit that is measured, but a change in resistance depending on the temperature, which should change smoothly and not jump.
Is it possible to repair the thermostat or just change it?
The question of repair thermostat often arises due to the desire to save money. However, the design of this device is such that it is a sealed unit. Inside there is a sealed capsule with gas or liquid that controls the mechanics of the contacts.
If the malfunction is caused by oxidation of the contacts, theoretically you can try to disassemble the case, clean the contacts with fine sandpaper and put it back together. But this is a temporary measure. The tightness will be broken, and after a short time the problem will return, possibly with more serious consequences.
In 95% of cases, especially when the bellows tube loses its tightness or the spring mechanism breaks, the device only needs to be replaced. The cost of a new thermostat is, as a rule, low, and the risk of repeated breakdown after a “makeshift” repair is too high.
- 🛑 Do not try to solder the thermostat body - the gas inside may ignite or evaporate.
- 🔍 When purchasing a new part, pay attention to the length of the capillary tube and markings.
- 🏭 Original spare parts last longer, but high-quality analogues are also acceptable.
Replacement takes a little time if you have access to the unit. The main thing is to correctly install and secure the capillary tube in its normal place, otherwise the new thermostat will not work correctly.
Does the type of refrigerant affect the choice of thermostat?
Yes, it does indirectly. Thermostats are selected for the operating temperature range of a specific refrigerant (freon). For example, R134a and R600a may require different trigger points. When purchasing an analogue, it is important to check not only the fitting dimensions, but also the temperature characteristics indicated in the marking.
Why did the refrigerator begin to work longer after replacing the thermostat?
This may be due to incorrect installation of the capillary tube. If it does not fit tightly enough to the evaporator or is installed in the wrong hole, the sensor will “see” the temperature incorrectly. It is also possible that the new thermostat has a slightly different adjustment range.
Can dirt on the contacts cause a malfunction?
Yes, oxidation or carbon deposits on the contacts inside the thermostat will increase the contact resistance. This leads to heating, burning of contacts and eventual sticking or complete break of the circuit. However, it is impossible to clean them without disassembling the sealed housing.
How often should you change the thermostat?
The service life of the thermostat is usually 5-10 years or more. It does not require scheduled replacement. They change it only when signs of a malfunction appear: constant operation of the compressor or a complete refusal of the refrigerator to turn on.