A sudden stop in the operation of a refrigeration unit or, conversely, its endless cooling cycle often confronts the owner with a difficult choice: call a technician or try to find the cause on his own. One of the key elements responsible for maintaining a given temperature is thermostat. It is this small device that commands the compressor when to turn on and when to stop, keeping the food fresh.
If you notice that the chamber has become too cold and the food is freezing, or the temperature has risen to room temperature, the first thing you should suspect is this particular unit. However, blindly replacing a part may not solve the problem if the diagnosis is carried out incorrectly. In this article we will look at how check the refrigerator thermostat in various ways, from simple observations to the use of measuring instruments.
Understanding the operating principle of this device will help you save time and money by eliminating false diagnoses. We will look at the symptoms characteristic of a malfunction thermostatand step-by-step describe the process of testing it.
The principle of operation and the role of the thermostat in the system
The thermostat, or thermostat, is an electromechanical device that responds to changes in temperature inside refrigeration chamber. Inside the housing there is a sealed tube (bellows) filled with gas or liquid, which expands when heated and contracts when cooled. When the temperature reaches a predetermined threshold, the pressure in the bellows changes, opening or closing electrical contacts.
Modern models such as Liebherr or Boschmay use electronic sensors, but most domestic refrigerators, including older models Atlant i Indesit, there are mechanical regulators. Their task is to maintain temperature balance, preventing food from defrosting or deep freezing in the refrigerator compartment.
If the mechanism sticks or the contacts oxidize, the compressor stops receiving the correct signals. This leads to two main scenarios: either the refrigerator works without interruption, trying to achieve unattainable cold, or is silent, allowing the temperature to rise. Diagnostics it begins with an analysis of the behavior of the compressor and temperature indicators.
⚠️ Attention: Before starting any work on dismantling or checking electrical circuits, be sure to disconnect the refrigerator from the power supply. Working with 220V voltage without proper qualifications is life-threatening.
It is also worth noting that in some models with the system No Frost the thermostat can control not only the operation of the compressor, but also defrost cycles. Therefore, its malfunction can lead to ice fouling on the evaporator and cessation of air circulation.
Main signs of a malfunctioning thermostat
You can determine that the problem lies in the thermostat by a number of indirect signs. Users often confuse a regulator breakdown with a freon leak or a compressor malfunction, which leads to unnecessary costs. Let's highlight the key symptoms indicating a defective thermostat.
- 🧊 The refrigerator does not turn off: The compressor works continuously, the humming does not stop for days, and a “snowdrift” or ice crust forms inside the chamber.
- 🌡️ No cold: The motor is silent, the chamber is warm, but when the thermostat contacts are forced to close, the compressor starts and cools normally.
- 💡 Spontaneous turning on of the light: In some circuits, the light in the chamber comes on only when the compressor stops; if the light is on constantly, the thermostat contacts may be open.
- 🔌 Short circuit: When you turn the control knob, you hear a sparkling crackle or knock out plugs in the apartment.
Important distinguish between situations when the refrigerator simply does not turn on for a long time due to a small amount of freon, and when it does not turn on due to an open circuit. If, when you turn the thermostat knob, you don’t hear a characteristic click at all, this is an alarming signal. In good condition, when scrolling the regulator from minimum to maximum, you should hear a clear click opening or closing of contacts.
Another sign is incorrect operation depending on the position of the knob. For example, a refrigerator cools only at maximum mode, but at minimum the compressor does not start. This indicates that the adjustment range thermostat is knocked down or the seal of the bellows is broken.
Visual inspection and initial check
Before picking up the multimeter, you need to conduct a visual assessment of the condition of the device. The thermostat is usually located inside the refrigerator compartment (on the wall or under a lamp shade) or outside, depending on the model. In refrigerators Stinol or Biryusa it is often hidden behind a plastic panel.
First of all, assess the condition of the capillary tube. This is a thin copper or steel tube that extends from the thermostat housing and is attached to the evaporator. If traces of corrosion, creases, cracks are visible on it, or it is completely disconnected from the evaporator, then tightness it is broken. The gas has evaporated and the device no longer responds to temperature.
Also pay attention to the contacts. If it is possible to remove the protective cover, inspect the terminals. The presence of oxides, carbon deposits or melted insulation indicates poor contact, which could lead to failure of the unit. Sometimes it is enough to simply clean the contacts to restore operation, but more often it is necessary to replacement the entire node.
| Symptom | Probable cause | Action |
|---|---|---|
| Does not click when turning | Mechanism jammed or broken | Replacing the thermostat |
| The tube is disconnected | Mechanical damage | Attempt fastenings or replacement |
| Crackling sparks are heard | Contacts burning | Urgent replacement to avoid fire |
| The refrigerator does not turn off | Contacts sticking in position "On" | Diagnostics with a multimeter |
If there are no visual defects, we move on to more accurate testing methods. You should not ignore the burning smell - it may indicate that a short circuit has occurred inside the thermostat housing, and further operation is impossible.
Diagnostics of the thermostat with a multimeter
The most accurate way to check the serviceability thermostat is to use a multimeter in continuity mode (ohmmeter). This method allows you to determine whether the electrical circuit closes and opens when the temperature of the sensing element changes.
To carry out the test, you will need to remove the thermostat from the refrigerator. Disconnect the wires, remembering or photographing their location. Connect the multimeter probes to the thermostat contacts. At room temperature, the contacts of most thermostats for the refrigeration chamber should be closed (the device will show 0 Ohm or emit a beep).
Now you need to cool the sensitive element. Place the capillary tube (or the body itself, if the tube is not removable, which happens in some models Electrolux) in a container with water and ice, or simply apply it to a very cool metal for a few minutes. When the temperature drops below the response threshold (usually about +5..+7°C), a click should be heard and the multimeter will show an open circuit (infinite resistance).
☑️ Checking with a multimeter
If the chain does not break even after strong cooling, then the mechanism is faulty and requires replacement. Likewise, if the circuit is open at room temperature and does not close when the case is heated in the hands, the thermostat is also considered defective. It is important to check all pairs of contacts, if there are several of them, since some models also control a fan or lamp.
⚠️ Attention: Do not test a thermostat connected to the network using a multimeter in resistance mode. This is guaranteed to lead to the tester fuse burning out and possible electric shock.
Testing method without instruments (imitation)
What to do if you don’t have a multimeter at hand and the refrigerator doesn’t work? There is a popular, but quite effective test method based on excluding the thermostat from the circuit. The essence of the method is to directly short-circuit the wires that went to the thermostat.
To do this, disconnect the wires from the thermostat and connect them directly to each other using twisting or insulating tape (after making sure that the refrigerator is unplugged!). After connecting, plug the refrigerator into the outlet. If the compressor starts up and begins to freeze, then the problem is 99% in the thermostat. However, this method requires extreme caution. By leaving the wires shorted, you force the compressor to start, which will run indefinitely until you disconnect the circuit. thermostat.
However, this method requires extreme caution. By leaving the wires shorted, you force the compressor to run, which will run indefinitely until you open the circuit. Never leave a refrigerator with shorted thermostat wires unattended for an extended period of time timeas this can lead to defrosting of food in the refrigerator compartment or failure of the compressor due to overheating.
This method is good for quick diagnostics in the field, when you need to understand whether the motor-compressor is alive. If the compressor is silent when the wires are closed, the problem may be deeper: the starting relay is faulty, the compressor itself is faulty, or the electrical wiring is broken.
What to do if the compressor hums but does not start?
This may indicate a jammed compressor or a faulty starting relay. In this case, directly connecting the thermostat will not help, and a more in-depth diagnosis of the motor will be required.
Specifics of testing in electronically controlled refrigerators
In modern models, such as Samsung or LG with a system No Frost and electronic control, a mechanical thermostat may be absent. Its role is performed by electronic temperature sensors (thermistors). Checking such elements differs from mechanical analogues.
Electronic sensors change their resistance depending on the temperature, but they do not click. To check them you also need a multimeter. You need to measure the resistance of the sensor at room temperature and compare it with the tabulated values for a specific model. Then the sensor is cooled and the resistance is measured again - it should change.
Often in such refrigerators, when the sensor breaks down, an error code lights up on the display. For example, this may be a series of blinking indicators, and this may be an alphanumeric designation on the screen. In this case, Bosch this may be a series of blinking indicators, and Whirlpool — alphanumeric designation on the screen. In this case diagnostics reduces to reading the error code and checking the corresponding sensor.
It is worth considering that in complex systems, control may depend on the software module. If replacing the sensor does not help, the control unit itself may be faulty and is not processing the signals correctly. In such cases, independent repair is difficult and requires special equipment.
Replacing and setting up a new thermostat
If diagnostics have confirmed a malfunction, the thermostat must be replaced. When purchasing a new part, pay attention not only to the appearance, but also to the technical characteristics: temperature range, capillary tube length and number of contacts. There are no universal solutions here; each refrigerator model requires a specific thermostat. The installation process is usually the reverse of the dismantling process. Carefully attach the capillary tube to the evaporator in the same place where the old one was. Insufficient contact of the tube with the surface of the evaporator will result in incorrect temperature readings. Use standard clamps or aluminum tape to secure. thermostat.
The installation process is usually the reverse of the dismantling process. Carefully attach the capillary tube to the evaporator in the same place where the old one was. Insufficient contact of the tube with the surface of the evaporator will result in incorrect temperature readings. Use standard clamps or aluminum tape to secure.
Adjustment may be required after installation. The body of a new thermostat often has three adjusting screws under a seal. It is not recommended to touch them without special equipment and knowledge, as you can throw off the factory calibrations. Usually, it is enough to simply set the control knob to the middle position and let the refrigerator return to mode for 5-8 hours.
If after replacement the refrigerator begins to behave strangely (for example, it turns on too often or does not get cold), check again that the tube is installed correctly and the connections are tight. Sometimes the problem lies not in the part itself, but in the installation.
Is it possible to use a thermostat from another refrigerator model?
In rare cases, this is possible if the temperature ranges and physical dimensions match. However, using a non-standard thermostat can lead to improper operation of the refrigerator, freezing of food or frequent on-off cycles, which will shorten the life of the compressor.
Why does the new thermostat not click?
Some new thermostats may not click at room temperature if their response range is shifted to the minus zone (for freezers cameras). It is also possible that the part is defective. In this case, checking with a multimeter is mandatory.
How often should you change the thermostat?
The service life of a high-quality thermostat is 10-15 years or more. Scheduled replacement is not required; it is changed only when signs of malfunction appear. Frequent breakdowns may indicate power surges in the network.
Does the type of refrigerant affect the choice of thermostat?
Directly - no, the thermostat reacts to temperature, and not to the type of freon. However, it has an indirect effect: different refrigerants may have slightly different temperature schedules of the system, so it is important to install the part with the range recommended by the manufacturer.