Has the refrigerator stopped maintaining the set temperature and food has started to spoil? Often the culprit is not the compressor, but a small but critical element - the thermostat. It is he who is responsible for turning the motor on and off at the right moment, maintaining the necessary microclimate inside the chambers.
Independent diagnostics of this part allows you to save time on calling a technician or even avoid unnecessary expenses if the problem is solved by simply replacing a cheap spare part. In this article, we will analyze all stages of the test: from visual inspection to testing with a multimeter, so that you can accurately determine the malfunction.
Before proceeding with disassembly, it is important to understand the principle of operation of the device. Thermoregulator reacts to changes in temperature in the evaporator and opens or closes the electrical circuit. If this mechanism jams, the refrigerator either freezes endlessly, turning into a freezer, or is silent, allowing the food to defrost.
Main signs of a malfunctioning thermostat
Diagnostics should begin long before you pick up a screwdriver. The behavior of your refrigerator will tell you where the problem lies. There are several characteristic symptoms that indicate a failure of the temperature sensor, and not a freon leak or a compressor breakdown. One of the most obvious signs is a motor-compressor without rest breaks. In normal mode, the equipment should turn off when the set temperature is reached. If the compressor hums for hours, and an ice coat forms inside the chamber, most likely, the thermostat contacts are stuck in the closed position.
One of the most obvious signs is continuous operation motor-compressor without rest breaks. In normal mode, the equipment should turn off when the set temperature is reached. If the compressor hums for hours and an ice coat forms inside the chamber, most likely the thermostat contacts are stuck in the closed position.
- 🔊 The compressor works without interruptions or does not turn on at all, remaining cold.
- ❄️ B a “snow coat” is formed in the refrigerator compartment or, conversely, the food is warm.
- 🔌 Abrupt shutdown of the appliance immediately after an attempt to start the motor.
⚠️ Attention: If the refrigerator hums, but does not cool, and the compressor is hot and the condenser (grid at the back) is cold, this may indicate a freon leak, not a thermostat failure. In this case, replacing the sensor will not help.
It is also worth paying attention to the nature of the shutdown. If the unit turns off, but after 2-3 minutes it starts sharply again, making a clicking sound, this is a sign that the circuit is not opening correctly. Mechanical wear The bimetallic plate inside the sensor causes it to stop responding to the heating of the evaporator.
In some models, especially modern ones, the malfunction may be accompanied by blinking indicators on the control panel. However, in older mechanical models, the only signal is an incorrect temperature regime. It is important not to confuse a thermostat failure with a malfunction of the start-up relay, the symptoms of which are sometimes similar.
Preparation for diagnostics: tools and safety
Any work related to the electrical components of household appliances requires compliance with safety rules. Before you start checking the thermostat, you must completely turn off the power to the refrigerator. Unplug the power cord from the outlet - this is a mandatory condition, ignoring which may result in electric shock.
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be multimeter (tester), which allows you to measure the resistance of the circuit. Without it, the check will be only approximate and will not give a 100% guarantee of the serviceability of the part.
- 🛠️ Screwdrivers (phillips and flat) for removing casings and fastenings.
- 🔌 Multimeter with continuity or resistance measurement mode (Ohm).
- 🧤 Gloves to protect hands from sharp edges and cold.
You may also need a container to collect water if condensation or ice has accumulated inside the chamber. Some thermostat models, especially capillary ones, have a long tube that must be carefully removed. Be prepared for the fact that access to the sensor may be difficult due to the design features of a particular model Indesit or Atlant.
It is important to prepare the workplace in advance. You will need a good light source as the thermostat is often located in hard to reach areas hidden by plastic panels. Do not use open sources of fire to defrost ice if it interferes with access - this will damage the plastic elements.
Removing the thermostat: step-by-step instructions
The process of removing the thermostat may differ depending on where it is located: inside the refrigerator compartment or outside, on the back wall. In most modern models, such as Bosch or LG, the temperature regulator is combined with the control knob inside the chamber.
First, remove the temperature regulator knob. It is usually simply pulled together by hand or secured with a small screw under a decorative plug. After removing the handle, you will have access to the fastening elements of the thermostat itself. Carefully unscrew them, trying not to lose small parts.
☑️ Checklist before dismantling
If the thermostat is located outside (often found in models Atlant and some old Soviet refrigerators), you will need to remove the top cover or back panel. Unscrew the fastening screws, carefully bend the clamps and gain access to the back of the evaporator, where the sensor bulb is fixed.
The most crucial moment is disconnecting the wires. Before removing the terminals, it is strongly recommended to take a photo of the wiring diagram. The colors of the wires may not comply with the standards, and it is very easy to confuse them during assembly. Contact markings will help to avoid mistakes.
⚠️ Attention: The capillary tube of the thermostat is very thin and fragile. When removing the sensor from the mounting socket, do not use excessive force so as not to damage the tube or break the tightness of the system if you plan to reuse the part (although this is rare).
After disconnecting the wires, carefully pull the sensitive element (capillary) out of the evaporator. It can be fixed in a special channel or pressed with a bar. Inspect the installation site for corrosion or signs of oxidation that could cause poor contact.
Checking the thermostat with a multimeter
The most accurate diagnostic method is to check the resistance with a multimeter. This method allows you to determine whether the circuit closes when the temperature changes. To begin, put the device in resistance measurement mode (usually indicated as 200 Ohms) or in dial mode.
Connect the multimeter probes to the thermostat contacts. At room temperature (about 20-25°C), most thermostat contacts should be closed and the device will show resistance close to zero or make an audible signal. If the device shows one or infinity, the circuit is broken and the thermostat is faulty.
However, simply checking at room temperature is not enough. It is necessary to ensure that the contacts open when cooled. To do this, immerse the sensitive part of the thermostat (capillary with flask) in a container with cold water and ice. The water temperature should be about 0...+5°C.
Why is it important to check in cold water?
The bimetallic plate inside the thermostat reacts to gas compression in the capillary. At room temperature, the gas expands and closes the contacts. When cooled, the gas contracts and the mechanism must break the chain. If this does not happen, the regulator will not turn off the compressor.
Soak the thermostat in cold water for several minutes so that it has time to cool down. Then take measurements again with a multimeter. If the thermostat is working, the resistance should increase to infinity (open circuit), signaling that at this temperature the compressor should be turned off.
The table below shows approximate values for different states of the thermostat:
| State | Environment temperature | Multimeter readings | Action |
|---|---|---|---|
| Normal (heat) | +20°C | 0 Ohm (Sound) | Contacts closed |
| Normal (cold) | +5°C | Infinity | Contacts open |
| Fault | Any | Always 0 Ohm | Stuck contacts |
| Fault | Any | Always infinity | Open circuit |
If you are using an electronic thermostat (thermistor), the technique changes. Here, it is not the closure that is checked, but the change in resistance depending on temperature. The values should change smoothly as the sensor heats up or cools down. Sharp jumps or lack of response indicate failure of the semiconductor element.
Visual inspection and search for hidden defects
Even if the multimeter shows normal values, not visual inspection should be ignored. Mechanical damage may not appear immediately. Carefully inspect the thermostat housing for cracks, melting or traces of burning. The presence of a black coating on the contacts indicates a spark has jumped and burnt.
Pay special attention to the capillary tube. It should not have creases, kinks or signs of corrosion. If the tube is deformed, the gas pressure inside the system does not change correctly, resulting in false temperature readings. In such cases replacing the thermostat is the only solution.
Check the condition of the wire insulation. Often, as a result of vibration of the compressor or natural aging, the insulation cracks, which can lead to a short circuit to the refrigerator body. This not only disables the equipment, but also creates the risk of electric shock when touching metal parts.
Also inspect the thermostat seat in the evaporator. There should be no ice or debris that could interfere with heat transfer. If the sensor does not fit tightly to the surface of the evaporator, it will read the air temperature, and not the actual temperature of the cooling element, which will lead to incorrect operation.
Replacing and setting up a new thermostat
If diagnostics confirm a malfunction, it is necessary to replace it. You should strictly buy the model that is indicated in the technical documentation of your refrigerator, for example TAM-133 for Atlant or K-59 for Indesit. Universal analogues may not be suitable for the capillary length or temperature range.
Installation is carried out in the reverse order of removal. Insert the capillary tube into the hole until it stops, carefully secure the housing with screws. When connecting wires, be guided by the photo or color marking you took earlier. Make sure the terminals are tight and not loose.
After assembly, do not rush to load products. Turn on the empty refrigerator and let it run for 2-3 hours. This will allow the system to get up to speed and test how the new thermostat controls the on and off cycles. The compressor should turn off when the temperature inside reaches normal.
If the refrigerator is equipped with a mechanical regulator with graduation (numbers 1-7), initially set the average value. After a day, check the temperature in the chamber using an external thermometer. If it differs from the required one (+3...+5°C), make an adjustment by turning the knob one notch.
What to do if the new thermostat does not fit the length of the capillary?
If the capillary tube of the new thermostat is longer, it can be carefully rolled into a ring and secured in the free space behind the panel, being careful not to bend it. If the tube is shorter, this is a problem, since the sensor may not reach the control zone. In this case, it is better to look for another model or use heat-conducting paste to improve contact if the gap is minimal.
Is it possible to temporarily close the thermostat?
Theoretically, by closing the contacts, you will force the compressor to work constantly. This will allow you to resuscitate food in an emergency, but you cannot leave the refrigerator in this mode for a long time. The compressor will burn out from overheating, and the food in the chamber will freeze. This is a temporary measure for a maximum of several hours.
Why does the thermostat click, but the refrigerator does not turn on?
The click means that the thermostat is properly sending a signal to turn on. The problem in this case lies deeper: most likely, the compressor starting relay has failed or the motor itself cannot start. Diagnostics of the compressor compartment is required.
How often should the thermostat be changed?
The service life of the thermostat usually coincides with the service life of the refrigerator (10-15 years). No scheduled replacement required. They change it only when signs of a malfunction appear: a violation of the temperature regime or a refusal to turn on.
Does the brand of the refrigerator affect the difficulty of replacement?
Yes. In refrigerators LG or Samsung with the No Frost system, access to the thermostat often requires complete disassembly of the internal panel, which is more difficult than in simple models Biryusa or Saratov, where the sensor is located outside or under the lampshade.