Sudden increase in temperature in refrigerator compartment or, conversely, the formation of an ice crust on the walls often indicates a malfunction of the temperature control system. If the compressor works continuously without turning off, or, on the contrary, remains silent for hours, causing the food to melt, then it is highly likely to fail. This small device is the “brain” that sends a command to turn the motor on and off depending on the sensor readings. thermostat. This small device is the “brain” that commands the motor to turn on and off depending on the sensor readings.
Before calling a technician or buying a new refrigerator, it makes sense to conduct independent diagnostics. Replacing the thermostat is one of the most common procedures in household repairthat can be performed at home with a minimum set of tools. Understanding the principle of operation of the device will help you save a significant amount and quickly return the equipment to life.
In this article we will analyze all stages of the process: from identifying symptoms to installing a new part. You will learn how to properly check the contacts with a multimeter, where to look for the unit in different models and what nuances to pay special attention to during installation.
Signs of a malfunctioning thermostat
The first step in restoring the functionality of the equipment is correct diagnosis. A thermostat, or thermostat, is a mechanical or electronic relay that opens and closes an electrical circuit. When it breaks, the refrigerator stops responding correctly to changes in temperature inside the chambers. The most striking symptom is continuous operation of the compressor. You hear the hum of the motor, it is hot to the touch, but the stop cycle never occurs.
The second scenario is exactly the opposite: the refrigerator is silent. The compressor does not start at all, the light in the chamber is on, but there is no cold. This indicates that the contacts inside the thermostat have oxidized or burned out, and the signal to start the engine simply does not pass through. In some cases, you can observe periodic failureswhen the equipment operates jerkily, which also indicates instability of the sensor.
⚠️ Attention: If the refrigerator stops freezing, do not rush to blame the thermostat. Similar symptoms can occur if there is a freon leak or a faulty start relay. Before disassembling, make sure that the condenser (grid at the back) is not cold and there are no obvious signs of mechanical damage to the tubes.
It is also worth paying attention to the condition of the food and ice. If a “coat” of ice appears in the chamber even with minimal settings, or the ice cream has become soft and the milk has turned sour, these are direct indications that it has been lost. In electronic models, an error may light up on the display, indicating a problem with the sensors, although mechanical thermostats do not give such signals. temperature control lost. In electronic models, an error may light up on the display, indicating a problem with the sensors, although mechanical thermostats do not give such signals.
The design and principle of operation of the thermostat
To carry out a quality repair, you need to understand what exactly you are dealing with. Classic mechanically controlled refrigerators use a capillary thermostat. Its design is quite simple, but reliable. The main element is bellows tubefilled with a temperature-sensitive gas (freon). This tube is attached to the evaporator or inserted inside the chamber.
When the temperature changes, the gas inside the tube expands or contracts, changing the pressure on the bellows. This mechanical movement is transmitted to a group of contacts, closing or opening the compressor power circuit. At the control handle, you set the spring force, which determines at what pressure (i.e. temperature) the switch will occur. In modern models, they are increasingly found Electronic thermostats, where the role of the sensitive element is played by a thermistor.
Electronic sensors transmit data to the main control board, which already makes the decision to start the motor. They are considered more accurate, but are more difficult to diagnose without special equipment. Mechanical devices, such as popular models Tam-133 or K-59are checked with a conventional tester. Differences in design also dictate different approaches to replacement: mechanics can often be changed “on the spot,” while electronics require deeper intervention in the control system.
What is the difference between a single-contact and two-contact thermostat?
Single-contact thermostats simply turn the compressor on and off. Two-pin (with three pins) have an additional contact for an indication lamp or for controlling a fan. When replacing, it is important not to mix up the wires, otherwise the compressor indicator may be on constantly or not at all.
Understanding the type of device you have is critical to purchasing the correct spare part. If you try to set a thermostat with different temperature response characteristics, the refrigerator will not work correctly: it will either underfreeze food or overfreeze it. Therefore, when looking for an analogue, always look at marking the old part.
Necessary tools for repair
To successfully carry out work on replacing the thermostat, you will need to prepare a workplace and a set of tools. Do not begin disassembly if you do not have the basic equipment at hand, as this may damage fragile plastic elements or wire insulation. The main tool is a set of screwdrivers (phillips and flat), since mounting screws can be of different types.
The second most important tool is multimeter (tester). Without it, it is impossible to accurately determine whether the old thermostat is working or the problem lies deeper. You will need to “ring” the contacts for the passage of electric current. A wire stripper is also useful if you need to increase the length of the capillary tube or replace the terminals, and electrical tape or heat shrink to insulate the connections.
- 🔧 A set of screwdrivers of various sizes for dismantling panels.
- 🔌 Multimeter for checking integrity of the electrical circuit.
- ✂️ Pliers or side cutters for working with wires and clamps.
- 🧤 Work gloves to protect hands from sharp edges and cold.
Sometimes a hair dryer may be needed to gently soften frozen plastic or remove icy elements, but it must be used with extreme caution so as not to melt the parts. Also prepare a container for defrosting if the work requires complete defrosting of the unit. Take care in advance of good lighting of the work area, since it is often dark inside the refrigerator, and it can be difficult to see small markings on the wires.
☑️ Preparation for repair
Removing the old thermostat
The process of removing the faulty part depends on the design of your refrigerator. In most top-freezer models, the thermostat is located inside the refrigerator compartment, often hidden behind a plastic panel or built into the temperature control knob. The first step is to de-energize the unit by removing the plug from the socket. This is a mandatory safety rule.
Remove the temperature control knob by gently pulling it towards you. There may be a locking screw underneath that needs to be unscrewed. Next, remove the decorative trim or lampshade if the thermostat is combined with them. In some models, for example, from the brand Indesit or Ariston, access to the unit opens after removing the top cover of the refrigerator, which is held on by several screws.
After gaining access, you will see the thermostat itself with a long thin tube coming out of it - a capillary. It can be fixed to the evaporator using a special clamp or simply pressed against the wall. Carefully disconnect the wire terminals from the thermostat contacts. It is highly advisable to take a photograph of the wire connection diagram before disconnecting, so as to avoid mistakes when installing a new element.
⚠️ Attention: The capillary tube is very thin and easily breaks or gets pinched. When removing the old thermostat, proceed slowly, without sudden jerks. If the tube is attached to the evaporator, be careful not to damage the heat exchanger.
Remove the old thermostat by carefully pulling the capillary tube out of its seat. If it is frozen, let the refrigerator sit at room temperature for a while or carefully use a hair dryer on low power. After removal, inspect the installation site for corrosion or damage to the insulation.
Diagnostics and testing with a multimeter
Before throwing away the removed part or buying a new one, it makes sense to finally make sure of the diagnosis. To do this, use a multimeter switched to continuity mode (usually indicated by a speaker or diode symbol). If you have a mechanical thermostat, it has two or three contacts. The multimeter probes must be applied to the main contacts (usually contacts 3 and 4, or 3 and 6, depending on the marking).
At room temperature, the contacts must be closed (the device beeps), since the temperature in the chamber is above the shutdown threshold. If you place the thermostat sensing tube in the freezer or press it against ice for a few minutes, the contacts should open (the beeping stops). If the circuit does not ring either in a cold or warm state, or vice versa - it rings constantly regardless of temperature, it means the thermostat is faulty and requires replacement.
For electronic thermostats (thermistors), the check consists of measuring the resistance. It should change smoothly as the sensor temperature changes. Sudden jumps in resistance or an open circuit indicate a breakdown. The exact resistance values for a specific model can be found in technical reference books or service manuals.
| Contact status | Multimeter reading | Diagnosis | Action |
|---|---|---|---|
| Heat (room temp.) | 0 Ohm (There is sound) | Normal | Cool the sensor |
| Cold (after freezer) | ∞ Ohm (Sound no) | Normal | Replacement not needed |
| In any condition | ∞ Ohm (No sound) | Open circuit | Replacement thermostat |
| In any condition | 0 Ohm (There is sound) | Sticking | Replacing the thermostat |
Installation of a new thermostat and configuration
Installation of a new part is carried out in the reverse order of dismantling. Insert the capillary tube of the new thermostat into the same hole where the old one was, being careful not to bend it. The immersion depth of the sensitive element must correspond to the original, otherwise the temperature readings will be incorrect. Secure the tube with a standard clamp or clip on the evaporator.
Connect the wires to the contacts of the new thermostat strictly according to the photograph or diagram you made earlier. Make sure the connections are secure and not loose. If the terminals are old and oxidized, it is better to replace them with new ones to ensure good contact. After assembling the plastic panels and installing the regulator knob, you can turn on the refrigerator.
The first start-up may take some time. Let the refrigerator run for several hours without loading food to allow it to return to normal. Check if the compressor turns off after reaching temperature. If the refrigerator operates normally, turning on and off cyclically, it means the repair was completed successfully.
⚠️ Attention: The characteristics of thermostats from different manufacturers may differ. If after replacement the refrigerator starts to turn on frequently or, conversely, does not freeze well, perhaps the installed thermostat has a different temperature range. In this case, replacement with a model with a similar marking is required.
During operation, monitor the operation of the unit on the first day. Make sure that no excess ice forms in the chamber and that the food is cooled evenly. A correctly selected and installed thermostat will ensure long and stable operation of your refrigerator.
Frequently asked questions (FAQ)
Is it possible repair the thermostat rather than change it?
In most cases, repairing a mechanical thermostat at home is impossible and impractical. The device is a sealed unit, and damage to its integrity will result in loss of sensitive gas. Electronic sensors also cannot be repaired, only replaced. Attempts at disassembly usually end in the final breakdown of the part.
Why does the new thermostat click, but the refrigerator does not turn on?
The click means that the mechanics of the thermostat are working and the contacts are trying to close. If the compressor is silent, the problem may be with the compressor itself, the start relay, or the wiring. It is also possible that the new thermostat is faulty out of the box or is not wired correctly. It is necessary to ring the circuit from the thermostat to the compressor.
How often do you need to change the thermostat?
The service life of the thermostat is on average 5-10 years, but depends on the intensity of use of the refrigerator and the quality of the electrical network. Voltage surges can damage contacts ahead of time. Planned replacement is not required, repairs are made only after a breakdown.
Does the length of the capillary tube affect the operation?
Yes, the length and method of laying the capillary tube affect the reaction speed of the thermostat. If the tube is too long, it cannot be twisted or cut too much (unless this is provided for by the design), as this will change the volume of the sensitive element and the temperature response characteristics.