Sudden defrosting of food, the appearance of puddles on the kitchen floor, or, conversely, the transformation of the freezer into an icy monolith - all these are sure signs that thermostat your refrigerator is out of order. This small but critical unit is responsible for maintaining the set temperature by turning the compressor on and off based on a sensor signal. If it starts to “lie” or simply stops closing the circuit, the refrigerator either works endlessly, trying to catch up with a non-existent cold, or stands silently, allowing food to spoil.
Before calling a technician or buying new equipment, it is worth conducting independent diagnostics. In most cases, verification thermostat does not require complex equipment and is available to any home craftsman with a basic set of tools. However, it is important to understand that we are talking about an electrical device, therefore compliance with safety measures and sequence of actions here is an absolutely mandatory condition for successful and safe repair.
In this article we will analyze not only the theoretical aspects of the operation of the thermostat, but also practical steps by testing it with a multimeter. You will learn how to distinguish a broken thermostat from other malfunctions, which models require a special approach, and whether it is even worth taking on the replacement yourself. Competent diagnostics will save you money and time, allowing you to accurately determine the culprit of the problem.
The operating principle and design of the thermostat
The thermostat, or thermostat, is an electromechanical device that responds to changes in the temperature of the refrigerant or air in the chamber. Inside the case there is bellows tubefilled with gas or liquid that is sensitive to thermal fluctuations. When the temperature in the chamber rises, the gas expands, the pressure in the tube increases, and the membrane closes the electrical contacts, starting the compressor.
As soon as the set cold threshold is reached, the pressure drops, the spring opens the contacts, and the engine stops. Modern models, such as Indesit or Atlant, may use electronic thermostats based on thermistors, but the principle remains the same: control of the compressor operating cycle. Understanding this mechanism is necessary for correct interpretation of test results.
Structurally, the device consists of a housing, a control knob, a bellows tube (capillary) and a group of contacts. It is the contacts that are most often subject to wear or burning, which leads to loss of conductivity. The tightness of the bellows may also be broken, causing gas to escape and the relay to stop responding to heat.
⚠️ Attention: The capillary tube of the thermostat is very thin and fragile. If you carelessly remove or install a new relay, it can easily be damaged, which will instantly damage the part. Work with it extremely carefully, avoiding kinks.
There are two main types of relays: mechanical (with a bellows) and electronic. Mechanical ones are more common in budget and older models; they are repairable in theory, but in practice they must be replaced. Electronic ones require checking the thermistor resistance, which is also done with a multimeter, but taking into account temperature coefficients.
Main signs of a thermostat malfunction
You can determine that the problem lies in the thermostat by the characteristic symptoms that appear in the operation of the refrigeration unit. The most obvious sign is that the compressor either does not turn on at all, or runs continuously without turning off for hours. In the first case, the products deteriorate, in the second, a “fur coat” grows on the walls of the chamber, and the engine overheats.
Another alarming signal is the incorrect operation of the indicators or the absence of a click when turning the regulator knob. If you turn the knob from minimum to maximum, and there is no characteristic sound of opening/closing contacts, this is a direct indication of mechanical jamming or broken elements.
- 🧊 No cold: The compressor is silent, the chambers are warm, the light is on, but the engine does not start even when the regulator is set to maximum.
- 🔊 Constant hum: The refrigerator hums continuously, the walls freeze, but automatic shutdown does not occur for a long time.
- 💡 Temperature jumps: Food either freezes into ice or begins to thaw, although you have not changed the regulator settings.
It is also worth paying attention to the state of the regulator itself. If the handle turns too easily, without the characteristic spring force, or, conversely, sticks, this indicates an internal breakdown of the mechanism. In models with electronic control, the symptom may be an error on the display indicating a malfunction of the temperature sensor.
⚠️ Attention: Do not confuse a thermostat breakdown with a malfunction of the compressor start-up relay or the motor itself. If you hear a click when you turn it on, the hum lasts 5-10 seconds, then there is a click and silence - the problem is most likely in the compressor or start relay, and not in the thermostat.
Sometimes the cause of an “imaginary” thermostat breakdown is the displacement of the capillary tube. If it does not fit tightly to the evaporator or has jumped out of its seat, the sensor reads the wrong temperature and the refrigerator operates in emergency mode. Therefore, before replacing a part, always check that it is installed correctly.
Preparation for diagnostics and necessary tools
To properly check the thermal relay, you will need a minimum set of tools that most home craftsmen can find. The main device will be multimeter (tester), capable of measuring resistance (Ohm) and ringing the circuit. Without it, diagnostics will only be a challenge, since it is impossible to visually determine the integrity of the contacts inside the sealed case.
In addition to the multimeter, prepare a flat-head and Phillips screwdriver for dismantling the panels, as well as pliers with thin jaws. A flashlight may be required for ease of use, as thermostats are often located in hard-to-reach, dark places. If you are planning a replacement, find out the model of your refrigerator in advance to find a compatible spare part.
The most important preparation rule is to completely disconnect the appliance from the power supply. Any manipulations with the electrical components of the refrigerator should be carried out only after removing the plug from the socket. Neglecting this rule may result in electric shock or short circuit.
☑️ Preparing to check the thermostat
Before starting disassembly, it is recommended to photograph the location of the wires and their connection to the thermostat contacts. Color coding may vary between models, and mixed up wires will cause the compressor to malfunction or break down. The photo will become your insurance during reassembly.
Step-by-step instructions: how to get to the thermostat
The location of the thermostat depends on the design of the refrigerator. In most single-compressor models (for example, Biryusa, old Zanussi) it is located inside the refrigeration chamber. To get to it, you need to remove the plastic cover that hides the regulator knob and the light bulb.
In some models, such as Stinol or Indesit, the thermostat can be hidden behind the top panel ("roof") of the refrigerator or in a niche above the door. In dual-chamber No Frost systems, sensors are often located in the air ducts or behind the rear wall of the chamber, requiring more complex disassembly. Always refer to the instructions for the specific model.
The dismantling process usually looks like this:
- Remove the temperature control knob (sometimes you need to pry it off with a knife or thin screwdriver).
- Unscrew the screws securing the plastic panel or casing.
- Carefully remove the panel so as not to damage the wires.
- Disconnect the wire terminals from the thermostat contacts, remembering their location.
- Remove the bellows tube from the hole in the chamber (be careful not to pull sharply).
After removing the device, inspect it for visible damage: melting, cracks, signs of corrosion. Pay special attention to the entry point of the capillary tube into the body - there should be no traces of oil or rust, which may indicate depressurization.
⚠️ Attention: When removing the bellows tube from the refrigerator body, act as delicately as possible. If the tube is stuck, do not use force - it is better to carefully clear the passage so as not to damage the fragile capillary and not to break the tightness of the system.
If the thermostat is electronic, the procedure is similar, but instead of a long tube you will see a small sensor on the wire. Such devices are often attached to the evaporator with clips or special clamps. They are checked in the same way, but the resistance of the sensor itself is tested.
Checking a thermostat with a multimeter: algorithm of actions
The most reliable way to check the functionality of a thermostat is to ring its contacts with a multimeter. To do this, switch the device to resistance measurement mode (Ohm) or continuity mode. If the contacts are closed, the multimeter will show zero or a value close to it, and a beep will sound in the dialing mode.
First, check the main working contacts. In standard thermostats there are usually three of them: one general and two working (for the compressor and for the signal lamp). At room temperature, the contacts responsible for turning on the compressor must be closed. If the multimeter shows infinity (open), then the relay is faulty and is not supplying voltage to the motor.
Then perform an open circuit test. To do this, place the sensitive bellows tube in a container of hot water (about 50-60°C) for a few minutes. The heat will expand the gas inside and the contacts should open. If, after heating, the multimeter still shows a short circuit, it means that the thermostat is “stuck” and does not turn off the compressor.
Features of testing three-pin thermostats
In three-pin models, one contact goes to the compressor, the other to the light bulb in the chamber. When calling, it is important not to confuse the pairs. Typically, pins 3 and 4 (or 3 and 6) will close when cool, and pin 4 may be associated with a warning light. Call all pairs to understand the logic of operation of a particular instance.
For electronic thermostats, the technique is different: you need to measure the resistance of the thermistor at different temperatures. The resistance should change smoothly as the sensor heats up or cools down. A sharp jump or lack of response indicates failure of the element.
Compare the data obtained with the reference values for your model. The table below will help you navigate the main types of faults:
| Symptom | Multimeter readings | Diagnosis |
|---|---|---|
| The refrigerator does not turn on | Open circuit (infinity) at room temperature | The thermostat is faulty (does not close the contacts) |
| The refrigerator does not turn off | Circuit closure (0 Ohm) after heating the tube | The thermostat is faulty (does not opens the contacts) |
| Unstable operation | Floating readings, sparking | Burning of contacts or loss of tightness |
| Lamp does not light, there is cold | Breakage on lamp contact | The signal lamp circuit is faulty (rarely) |
If after all the checks you come to the conclusion that the thermal relay is faulty, it must be replaced with a similar one. Repair of internal mechanical parts is practically impractical due to the complexity and low reliability of the restored unit.
Diagnostic nuances for different brands
Different refrigerator manufacturers use different types of thermostats, which makes its own adjustments to the diagnostic process. For example, in refrigerators Atlant thermostats TAM-112 or TAM-133, which have a specific capillary tube length, are often used. When replacing, it is important to choose an analogue with the same or greater length, otherwise the refrigerator will not work correctly.
In technology Liebherr and Bosch there are often complex electronic control systems, where the thermostat is only one of the sensors. Here a simple test may not give a complete picture, since the control board may be responsible for the operation. In such cases, diagnostics require checking the signals on the board.
Refrigerators Indesit and Ariston are often equipped with thermostats mounted on the “roof” of the chamber. Their peculiarity is a short capillary tube, which is easily damaged if installed carelessly. Also, in these models, oxidation of contacts is often found due to high humidity in the mounting niche.
It is important to consider that in two-chamber refrigerators with a No Frost system, the thermostat can control not only the compressor, but also the defrost system. Its malfunction can lead to freezing of the evaporator and stopping the circulation of cold air, even if the compressor is working properly.
When buying a new thermostat, pay attention not only to the model, but also to the temperature range. There are relays for refrigerators, freezers and combined ones. Installing a relay that is not suitable for the range will either lead to constant frost or spoilage of food.
Frequently asked questions (FAQ)
Is it possible to temporarily short-circuit the thermostat to make the refrigerator work?
Technically, this is possible: connecting the wires bypassing the relay will start the compressor. However, this can only be done briefly to check the motor. Constant operation without a thermostat will lead to continuous frost, freezing of food and eventual breakdown of the compressor due to the lack of rest cycles. Use this method only as an emergency measure for a few hours.
Why doesn't the new thermostat click?
New thermostats may have a tighter spring or a different temperature response range. If there is no click when turning the knob, try cooling the bellows tube (for example, by applying an ice pack). If even after cooling there are no contacts, you may have been sold a defective part or a model with other parameters.
How can you understand that the problem is in the thermostat and not in the compressor?
If when you turn on the refrigerator into the network, the compressor is silent, but when you close the thermostat contacts directly (bypassing) it starts, it means that the motor is working, and the thermostat does not supply signal. If, with a direct connection, the motor hums, but does not start, or does not respond at all, the problem is in the compressor or start relay.
How much does it cost to replace a thermostat?
The cost of the thermostat itself varies from 500 to 2000 rubles, depending on the model and brand. The services of a replacement technician will cost an additional 1,500–3,000 rubles. Replacing it yourself saves the budget, but requires accuracy and basic skills.
Is it possible to adjust the thermostat without tools?
The temperature is adjusted using the knob on the body of the refrigerator. However, internal calibration (differential adjustment screw) requires a screwdriver and special knowledge. Without experience, it is not recommended to turn the internal screws - you can reset the factory settings, and the refrigerator will no longer maintain the temperature.
Diagnostics of the thermostat is a skill that can save your budget and products. Follow the instructions carefully, use quality tools and do not ignore safety precautions. If after checking the thermostat the problem is not solved, it may be worth paying attention to other components of the refrigeration unit.