Sudden cessation of operation of the refrigeration chamber or, conversely, the formation of an ice crust on food often indicates a malfunction in the temperature control system. The main element responsible for maintaining the set mode is the thermostat (thermostat). It is he who closes and opens the electrical circuit of the compressor depending on the sensor readings. If this mechanism fails, the refrigerator stops cooling or works without stopping, which threatens food spoilage and motor overheating.
Before calling a technician, many owners of household appliances try to diagnose the problem themselves. Understanding how to check a thermostatallows you to save time and money, and also quickly determine whether a complete replacement of the unit is required or a simple adjustment is sufficient. In this article, we will analyze in detail diagnostic methods, necessary tools and nuances of working with various types of thermostats.
Modern models of refrigerators, such as Bosch, Indesit or LG, can be equipped with both mechanical and electronic regulators. The principle of checking them has its own characteristics, but the basic logic of troubleshooting remains similar.
Main signs of a thermostat malfunction
The first step in diagnosis is to monitor the behavior of the refrigerator. Thermoregulator is the “brain” of the cooling system, and its breakdown manifests itself in characteristic symptoms. If you notice that the compressor turns on too rarely or, on the contrary, hums incessantly, this is the first cause for concern. In normal operation, on and off cycles should be periodic.
There are a number of obvious signs indicating the failure of this unit. Pay attention to the following points:
- 🧊 In the refrigerator compartment, the food has begun to deteriorate, and there is no frost on the walls, although the compressor is working.
- ❄️ A thick “coat” of ice has formed in the freezer, and the food is frozen.
- 🔇 Compressor does not turn on at all, and there is complete silence in the refrigerator (provided the socket is working properly).
- 🔥 The body of the refrigerator gets very hot, and the motor runs without interruption, trying to reach an unattainable temperature.
It is also worth listening to the sounds when turning the temperature control knob. In a working mechanical thermostat, a characteristic click should be heard at the moment of switching. If you turn the knob and there is no click, the contacts inside may be oxidized or stuck. This is especially true for models with a capillary tube, where mechanical wear occurs faster.
⚠️ Attention: If the refrigerator makes loud clicking noises but does not start, do not try to change the thermostat right away. Check the compressor start relay, as the symptoms may be similar.
Visual inspection and preparation for diagnosis
Before you start using measuring instruments, you must gain access to the thermostat. The location of this element depends on the design of the refrigerator. In most older models and some modern ones, such as Atlant or Stinol, it is located inside the refrigerator compartment. In other cases, for example, in Samsung or Haier, the thermostat can be hidden behind the top cover or in a niche above the door.
The preparation process requires care. First, completely unplug your refrigerator. Then release the top shelf and remove the lamp shade if it is in the way of access. Often the thermostat is mounted on a plastic box, to which an adjustment knob fits. By removing the decorative trim and unscrewing the screws, you will see the block itself with the wires suitable for it.
During a visual inspection, pay attention to the condition capillary tube. This is a thin copper or aluminum wire that goes deep into the housing or is attached to the evaporator. If the tube shows signs of corrosion, kinks, or is disconnected from its mounting location, the thermostat will not read the temperature correctly. Also check the integrity of the insulation of the wires going to the contact group.
In some models, for example, in refrigerators with a system No Frost, the thermostat can be built into the electronic control module. In this case, visual diagnostics are limited to checking the connectors for oxidation. If you see traces of plastic melting on the terminals, this indicates poor contact or overload, which requires replacing not only the thermostat, but also the connectors.
Diagnostics of a mechanical thermostat with a multimeter
The most accurate way check the refrigerator thermostat is to use a multimeter in dial mode. This method allows you to determine the integrity of the electrical circuit. To carry out the test, you will need to remove the thermostat from the refrigerator, disconnecting all the wires (after photographing their location).
The algorithm of actions is as follows:
- Set the multimeter to the resistance (Ohm) or continuity measurement mode.
- On the thermostat knob, select the minimum temperature value (usually this is maximum cooling).
- Touch the probes of the multimeter to the contacts of the thermostat.
- If the device makes a beep or shows zero, the circuit is closed and the thermostat is working.
If there is no bell at the minimum temperature, Turn the knob to the "Off" or maximum heat position. In this position, the circuit should open and the multimeter should be silent (show one or infinity). If the circuit does not break even in the “Off” position, then the contacts are stuck and the thermostat must be replaced.
☑️ Check with a multimeter
Particular attention should be paid to the contacts marked as “30” and “33” (or similar markings on the case). It is through them that the current passes to the compressor. The normal resistance of a working thermostat with the contacts closed should be close to 0 Ohm. Any jumps in the value or an intermittent signal indicate burning of the contacts inside the case.
Checking the thermostat with a capillary tube
The key element of a mechanical thermostat is capillary tube, filled with refrigerant (freon). It reacts to changes in temperature: it contracts when cooled and expands when heated, affecting the membrane and opening the contacts. It is more difficult to check the integrity of this system, since it requires simulating temperature conditions.
For the test you will need a container of cold water (about 0°C) and access to heat. Lower the end of the capillary tube (if it is removable) or the entire thermostat (if the design allows and there are no live electrical contacts, which is dangerous) into the cold. However, it is safer to check the reaction of the contacts to changes in temperature without immersing the electrical unit itself in water.
You can use a hair dryer to gently heat the sensitive element. If, when the tube is heated with a hairdryer, the contacts open (the signal on the multimeter disappears), and when it cools down, they close again, it means that the gas in the tube has not evaporated and the membrane is working. If there is no response to heating and cooling, it means that the system has depressurized and the freon has evaporated.
| Condition | Multimeter readings | Action |
|---|---|---|
| Normal (Cold) | 0 Ohm (There is a bell) | Good |
| Normal (Warm/Off) | ∞ (No bell) | Good |
| Open circuit | ∞ in any position | Replacement |
| Sticking | 0 Ohm in the "Off" position | Replacement |
⚠️ Attention: Do not heat the capillary tube with an open fire or a hair dryer at maximum power. This can lead to rupture of the thin-walled tube and complete failure of the unit.
Why does freon evaporate from the thermostat?
The freon in the capillary tube of the thermostat is under pressure. Over time, due to compressor vibrations and natural aging of the metal, microcracks may form in the tube. Corrosion is also often the cause of depressurization, especially in conditions of high humidity inside the chamber. freon comes out, the pressure stops changing, and the membrane stops moving, regardless of the actual temperature in the chamber.
Diagnostics of the electronic thermostat and sensors
In modern refrigerators, such as Liebherr or top models Beko, mechanical regulators replaced by electronic temperature sensors (thermistors). Checking them is different from diagnosing mechanics. There are no moving parts or capillary tubes, and the resistance changes depending on the temperature of the semiconductor element.
To check the electronic thermal sensor you also need a multimeter, but you need to evaluate specific resistance values that change smoothly. Typically at room temperature (20-25°C) the resistance is several kiloohms (for example, 5-10 kohms). When cooling, the resistance should increase (for NTC thermistors) or fall (for PTC).
If the multimeter shows an open circuit (one) or a short circuit (zero) regardless of temperature, the sensor is faulty. It is also worth checking the wires going from the sensor to the control board. Often, a break does not occur in the sensor itself, but at the point where the wire exits the housing or near the connector.
Electronic systems often have a self-diagnosis function. If the temperature sensor is faulty, error codes may appear on the refrigerator display. For example, it may be a flashing temperature indicator, and it may be an alphanumeric code on the screen. The decoding of the codes should be found in the instructions for the specific model. Indesit this may be a flashing temperature indicator, and Electrolux — alphanumeric code on the screen. The decoding of the codes must be found in the instructions for the specific model.
Replacing and adjusting a new thermostat
If the check confirms a malfunction, the only solution is replacement. Choose an analogue with exactly the same markings. Even visually similar thermostats may have different capillary tube lengths or different temperature response ranges. Installing an unsuitable part will lead to incorrect operation of the refrigerator.
The replacement process includes dismantling the old unit, installing a new thermostat in the seat and connecting the wires according to the previously made diagram. Pay special attention to securing the capillary tube. It must be tightly fixed on the evaporator or in a special channel, otherwise the sensor will indicate the air temperature and not the temperature of the cooling element.
After installation, adjustment may be required. Many thermostat housings have screws under a seal or hidden by a plug. Turning one screw changes the switching temperature, the other - the temperature difference (differential). They should be twisted very carefully, making no more than half a turn at a time, and waiting for the temperature in the chamber to stabilize.
Common mistakes when checking independently
Home craftsmen often make mistakes that lead to false conclusions. One of the most common is checking the thermostat, which has not been removed from the refrigerator, without taking into account the temperature. If the chamber is warm and you check the contacts, expecting a break, but the circuit is closed, this is normal. You need to cool the sensor.
Another mistake is ignoring the wiring condition. You can replace a working thermostat because the problem was an oxidized connector or a frayed wire. Always check the integrity of the circuit from the refrigerator plug to the thermostat entrance.
Also, do not forget about the defrost button, which is often built into the thermostat housing (especially in models ZIL or old ones Biryusha). If this button is stuck pressed, the refrigerator will not turn on. Check its mechanical movement and contacts.
When you need to call a specialist
Despite the availability of diagnostics, there are situations when self-repair is impractical. If your refrigerator is under warranty, any tampering with the design, including removing seals from the thermostat, will void the warranty. In this case, it is better to immediately contact an authorized service.
Also, professional help is needed if replacement requires complex disassembly of the housing, foaming of thermal insulation, or working with refrigerant (if a freon leak is suspected from the system, and not from the thermostat). The craftsmen have specialized tools for vacuuming the system and filling with freon.
⚠️ Attention: If you are not confident in your abilities or do not have basic skills in working with electrical appliances, do not take risks. Incorrect assembly can lead to a short circuit or fire.
In conclusion, correct diagnosis of the thermostat is the key to the long service life of your refrigerator. Timely replacement of this inexpensive component will save the compressor from overload and your products from spoilage. Regularly monitor the temperature conditions and listen to the operation of your unit.
Is it possible to check the thermostat without a multimeter?
It is impossible to accurately check without instruments. However, you can use the elimination method: if there is no click when you turn the knob and the refrigerator does not respond, most likely the problem is in the thermostat. You can also temporarily short-circuit the wires (bypassing the thermostat) - if the refrigerator starts working, then the thermostat is faulty. But this method is dangerous and requires caution.
Why does the new thermostat not fit the length of the tube?
Capillary tubes come in different lengths (from 0.5 to 3 meters). If the tube is too long, it can be carefully twisted into rings and secured inside the housing without bending it. If it is too short, replace it with a model with a suitable length, since it cannot be extended.
How often should the thermostat be changed?
The service life of the thermostat is on average 10-15 years. However, frequent power surges or mechanical damage can shorten this period. Scheduled replacement is not required; change only when signs of malfunction appear.
Does the type of freon in the refrigerator affect the choice of thermostat?
Yes, it does indirectly. Thermostats are selected for the temperature range and pressure in the system. Refrigerators using R600a (isobutane) often require thermostats with different response characteristics than R134a. Always look at the markings.