A sudden breakdown of refrigeration equipment always becomes an unpleasant surprise, especially when large stocks of food are stored inside. One of the key elements responsible for maintaining a stable temperature is thermostat (thermostat). It is this small device that controls the operation of the compressor, starting it when the temperature rises and turning it off when the set values are reached. If you notice that the chamber does not freeze or, on the contrary, the food turns into ice, the first thing you should suspect is this particular unit.
Diagnostics of the thermostat is a process that can be performed at home, without immediately resorting to the services of expensive technicians. However, to successfully carry out the work you will need a minimum set of tools and a basic understanding of the principles of electrical circuits. In this article, we will look in detail at how to identify the malfunction, what tools will be needed, and whether it is possible to extend the life of the old sensor or whether its replacement is inevitable.
Before you begin disassembling, it is important to understand that a thermostat is a mechanical or electronic switch that responds to changes in temperature conditions. Its failure often simulates a breakdown of the compressor or start relay, which can confuse an inexperienced technician. Modern models Refrigerators may have complex electronic control boards, but classic mechanical sensors are still widespread and can be repaired.
Main symptoms of a malfunction thermostat
You can determine that the problem lies in the thermostat by the characteristic symptoms that appear in the operation of the unit. Most often, users are faced with a situation where the compressor either does not turn on at all or works without interruption, causing excessive freezing of the evaporator. Understanding these signs will help you save time on initial diagnostics.
If the refrigerator is silent and warm inside, this may indicate that the contacts inside the sensor have oxidized or broken, and the signal to start the motor is simply not received. In the opposite situation, when the unit hums around the clock and does not turn off, the thermostat is “stuck” in a closed state, constantly requiring cooling. It is also worth paying attention to the following symptoms:
- 🧊 The chamber does not cool the food to the required temperature even with the maximum setting of the regulator.
- ❄️ A thick “coat” of ice forms on the back wall of the refrigerator compartment, and the food in the main chamber freezes.
- 🔌 The compressor beeps clicks when trying to start, but immediately stops, followed by a long pause.
⚠️ Attention: If your refrigerator makes strange noises or you smell a burning smell, immediately unplug it. Continuing to operate faulty equipment may result in a wiring fire or complete failure of the compressor.
It is important to note that similar symptoms can be observed with a refrigerant leak or a faulty start relay. Therefore, visual inspection and subsequent instrumental testing are mandatory steps. Do not rush to buy a new part until you are convinced of its inoperability using measuring instruments.
Sometimes the problem lies not in the sensor itself, but in the violation of the tightness of the bellows tube, which transmits temperature fluctuations. If a microcrack has formed in the freon circulation system, the pressure inside the tube drops and the contacts do not close. It is difficult to determine this visually, but an indirect sign may be the absence of a characteristic click when the tube cools, which we will talk about in the section on testing without instruments.
Necessary tools for diagnostics
To properly check the thermostat, you will need to prepare a workplace and a certain set of tools. Without them, it will be impossible to make an accurate diagnosis, since relying only on a visual inspection in this case does not make sense. The main device will be a multimeter, but you may also need auxiliary tools.
The list of necessary equipment includes both professional tools and items that are found in everyone’s home. It is important that the multimeter is in working order and has charged batteries, otherwise the readings may be incorrect. For work, prepare:
- 🔧 A set of screwdrivers (phillips and flat) for dismantling panels and removing the thermostat casing.
- 📏 Multimeter (tester) for continuity testing of the electrical circuit and checking resistance.
- 🧊 A container of cold water or ice to check the response of the bellows tube (with the sensor removed).
A multimeter is a universal device that allows you to measure voltage, current and resistance. To check the thermostat, we need a resistance measurement mode (Ohm) or a “continuity” mode, which signals with sound that the circuit is closed. If you do not have a multimeter, you can use a simple test (a light bulb with two wires), but this method is less accurate and requires caution when working with 220V mains voltage.
Also do not forget about personal protective equipment. Although the voltage in the thermostat circuit is usually low (as far as the control circuit is concerned), there is still a risk of accidental contact with other live parts of the refrigerator. Work in dry shoes and on a dry floor to prevent electric shock.
Removing the thermostat: step-by-step instructions
To check the thermostat, it must be removed from the refrigerator. The dismantling process may differ depending on the model and manufacturer of the equipment, but the general algorithm of actions remains similar. The main rule is to act carefully so as not to damage the plastic latches or break the capillary tube.
First you need to turn off the power to the refrigerator by removing the plug from the socket. This is a mandatory safety requirement. Next, find the location of the thermostat: in older models it is often located inside the refrigerator compartment on the side wall under a plastic casing, while in newer models it may be hidden behind a control panel on the door or at the top of the compartment. The removal process usually looks like this:
- Remove the temperature control knob (if it protrudes outward) by gently pulling it towards you.
- Unscrew the screws securing the protective casing or decorative trim.
- Carefully remove the thermostat housing, trying not to pull the capillary tube.
- Disconnect the terminals with wires, first remembering their location.
Particular care should be taken with the capillary tube. This is a thin copper tube containing gas or liquid inside. If you accidentally bend or damage it, the thermostat will stop responding to changes in temperature and will have to be replaced. In some models, the tube is fixed in a special hole in the wall of the chamber - you do not need to pull it out with force, just carefully unscrew the mount.
☑️ Preparation for dismantling
After removing the sensor, inspect it visually. There should be no cracks on the body, and the contacts should not have any traces of soot or melting. If you find obvious mechanical damage, further inspection may not be necessary - the part definitely requires replacement. However, if there are no visual defects, we proceed to instrumental diagnostics.
Checking the thermostat with a multimeter
The most accurate diagnostic method is to check the electrical circuit of the thermostat using a multimeter. This method allows you to say with 100% certainty whether the contacts close when the temperature changes. To carry out the test, switch the multimeter to resistance measurement mode (usually indicated by the Ω symbol) or to continuity mode.
First, connect the multimeter probes to the thermostat contacts. If your sensor has three contacts, then you need to call those that go from the network and to the compressor (usually these are two main contacts, the third can go to a light bulb or be grounding, the diagram is in the instructions for your model). At room temperature, the contacts should be closed, and the device will show zero or a resistance value close to it.
Next it is necessary to cool the sensitive element (bellows tube). To do this, place the tube in a container of ice water or simply apply ice to it. After a few minutes, when the sensor cools down, the contacts should open and the resistance on the multimeter will go to infinity (one on the left on the digital display). If this does not happen, then the thermostat is faulty.
| Condition | Multimeter readings | Contact action | Output |
|---|---|---|---|
| At room temperature | 0 Ohm (or close to 0) | Closed | Normal |
| When cooling | ∞ (Infinity) | Open | Normal |
| In any state | ∞ (Infinity) | Always open | Open circuit (Defect) |
| In any condition | 0 Ohm | Always closed | Sticking (Defect) |
It is important to consider that some thermostats have normally open contacts, which close only when the temperature drops. However, in household refrigerators, sensors that are normally closed at room temperature are most often used. If you are in doubt about the type of device you have, refer to the technical documentation for the specific model Indesit, Atlant or Beko.
Diagnostics without instruments: freezing method
What to do if you don’t have a multimeter at hand, but you need to check the refrigerator urgently? There is a popular method that allows you to indirectly assess the performance of the thermostat. It is based on the physical principle of operation of a bellows tube and does not require measuring instruments, but gives only an approximate result.
The essence of the method is forced cooling of the sensor. Remove the thermostat from the refrigerator, leaving the wires connected (observing safety precautions!). Gently immerse the bellows tube in a bowl of ice water or apply an ice pack to it. After 2-3 minutes, listen to see if there is a characteristic click of the contacts opening.
If there is no click, try closing the contacts manually (for example, with a paper clip, being careful). If the refrigerator compressor starts after the short circuit, then the problem is really in the thermostat, which does not open the circuit when cooling or does not close when heating. This method is good for an initial assessment, but does not guarantee accuracy.
⚠️ Attention: Never immerse the thermostat housing itself with electrical contacts in water! Only a metal capillary tube can be cooled. Moisture getting inside the case will lead to a short circuit and the impossibility of further use of the part.
You can also check the operation of the thermostat by assembling a simple circuit with a 220V light bulb. Connect the thermostat in series with the light bulb to the network. At room temperature the lamp should burn. When the tube cools, it goes out. This is a more reliable method than listening to clicks, but it requires skills in working with high voltage.
Replacing and setting up a new thermostat
If diagnostics confirm a malfunction, the thermostat must be replaced. There is no point in repairing it yourself: the tightness of the bellows system cannot be restored at home, and calibrating the contacts requires special equipment. You need to buy a part with exactly the same markings as the old sensor.
The process of installing a new part is done in the reverse order. Carefully insert the capillary tube into the mounting hole without bending it. Connect the wires according to the photo you took earlier. After assembling the refrigerator and connecting it to the network, you may need to adjust the temperature mode.
The thermostat housing often has adjusting screws hidden under a seal or plastic plug. They allow you to adjust the temperature at which the compressor turns on and off. Turning the screw clockwise usually increases the temperature difference (hysteresis), and counterclockwise - decreases it. However, it is not recommended to go there without a special thermometer, since you can reset the factory settings.
After replacing, let the refrigerator run for a few minutes hours without loading products. This will allow the system to return to operating mode and ensure that the new thermostat controls the on and off cycles correctly. If the temperature stabilizes within normal limits (usually +2...+5°C in the main chamber), the repair can be considered successful.
Can a universal thermostat be used?
Universal thermostats (for example, TAM-133) are often suitable instead of the original ones, but may differ in the length of the capillary tube or temperature range. Before purchasing, be sure to compare the parameters: operating temperature range, tube length and contact type. In some cases, the tube has to be carefully rolled into a ring so that it fits in the housing.
Frequently asked questions (FAQ)
Is it possible to drive with a faulty thermostat if I turn off the refrigerator myself?
Theoretically, it is possible, but this is extremely inconvenient and risky. You will have to constantly monitor the temperature and manually turn the equipment on/off. In addition, frequent manual cycles can negatively affect the life of the compressor, since it takes time to equalize the pressure in the system before starting.
Why does the new thermostat click, but the refrigerator does not turn on?
If there is a click, then the mechanics are working. The problem may be poor terminal contact (oxidation), a broken wire, or a malfunction of the compressor/start relay itself. Check the voltage at the output of the thermostat when the contacts are closed.
How much does it cost to replace a thermostat in the service?
The cost consists of the price of the part itself and the work of the technician. On average, replacement costs from 1,500 to 3,000 rubles, depending on the region and model of the refrigerator. Self-replacement will save the cost of work, which often amounts to 50% of the total amount.
What is the difference between a thermostat and a thermostat?
In the context of household refrigerators, these terms are often used as synonyms. However, technically, a thermostat is a device with an adjustable set point (knob), and a thermostat is a sensor with fixed values. In modern refrigerators, adjustable thermostats are more common.