A modern refrigerator is a complex engineering system, where each element performs a strictly defined function. The central link in the chain of maintaining cold is thermostat, which is often called the “brain” of the temperature regime. It is this small device that determines when the compressor needs to start the cooling cycle, and when it needs to stop to save energy.
If you notice that the food in the chamber has begun to freeze or, conversely, quickly deteriorate due to insufficient cold, the reason often lies in the incorrect operation of the sensor. Understanding how this unit works will help you carry out initial diagnostics yourself and avoid calling a technician for basic problems.
In this article we will analyze in detail the physical principle of operation of the device, consider its location in various models of equipment and compile a list of symptoms indicating the need for replacement. Attention: before any manipulations with electrical components, be sure to disconnect the device from network.
The principle of operation and design of the thermostat
The main task of the thermostat is to automatically open and close the electrical circuit that powers the compressor, depending on the temperature inside the refrigeration chamber. Inside the device there is a sensitive element - a bellows tube filled with refrigerant (freon, methyl chloride or other gas with a low boiling point). This gas reacts to the slightest changes in the thermal background.
When the temperature in the chamber rises above the value you set, the gas inside the tube expands. This expansion creates pressure on the bellows membrane, which mechanically closes the electrical contacts. At this moment, voltage is applied to the motor and the cooling process begins. As soon as the air reaches the desired level, the gas is compressed, the contacts open, and the compressor stops.
There are two main types of structures that can be installed in your equipment:
- 🔹 Mechanical thermostats - the classic version, where adjustment is carried out by a rotary knob that changes the spring tension.
- 🔹 Electronic sensors - more modern solutions that transmit data to the main control module, which already makes the decision to start the motor.
- 🔹 Combined systems - found in two-chamber models, where one sensor can control the operation of the dampers or evaporator.
It is important to understand that mechanical thermostat does not measure temperature accurately degrees, it reacts to the physical state of the gas. That is why turning the knob does not always mean an instant change in the climate inside - the system needs time to stabilize the pressure in the tube.
Location and signs of malfunction
The installation location of the thermostat directly depends on the design of the refrigerator. In single-chamber models, such as the old Atlant or Saratovs, the sensor is usually located inside the refrigerator compartment. It can be seen as a plastic handle with divisions or hidden under the lampshade.
In two-chamber units with one compressor the situation is different. Here the thermostat is most often located in the refrigerator compartment, but its capillary tube runs through the entire system and ends in the freezer or at the evaporator. In models with the system No Frost sensors may be built into the air ducts or located behind the rear wall.
⚠️ Attention: If you plan to remove the thermostat, be sure to photograph the wiring diagram. Mixed-up contacts can lead to a short circuit or failure of the compressor.
How to understand that the device has failed? There are several obvious symptoms that cannot be ignored:
- 🔹 The compressor works non-stop, creating a constant hum, and a “fur coat” of ice forms in the chamber.
- 🔹 The refrigerator is silent: the motor does not turn on at all, although the light inside is on.
- 🔹 Temperature jumps: food either freezes into ice, then thaws, even if you did not touch the regulator.
- 🔹 Clicks: frequent cyclic turning on and off of the motor with an interval of 2-3 minutes.
Why does the compressor not stop?
If the thermostat is “stuck” in the closed contacts position, it will constantly signal to start the engine, ignoring the actual temperature. This leads to excessive energy consumption and freezing of products.
Diagnostics begins with a visual inspection and listening to the operation of the unit. If when you turn the control knob you do not hear a characteristic click, this may indicate mechanical damage to the internal parts of the device.
Table of symptoms and causes
For ease of diagnosis, we have compiled a summary table that will help compare the observed behavior of the equipment with the probable cause of the breakdown. This will allow you to more accurately formulate the problem when ordering spare parts or communicating with a specialist.
| Symptom | Probable cause | Difficulty of repair |
|---|---|---|
| The motor does not turn on, there are no clicks | Breakage of contacts thermostat or lack of power | Low |
| Continuous operation of the compressor | Sticking contacts or gas leakage from the bellows | Medium |
| Short operating cycles (start-stop) | Incorrect calibration or tube displacement | Medium |
| Ice only at the back wall | Temperature setting too low (not broken) | Minimum |
Please note that the symptoms may overlap with malfunctions of the start relay or the compressor itself. Therefore, before replacing the thermostat, it is recommended to carry out an electrical test.
Instructions for testing with a multimeter
The most reliable way to make sure that the device is working is to ring its contacts with a multimeter. To do this, you will need to remove the device, having first disconnected the refrigerator from the power supply. Depending on the model, access to the thermostat may be through removing the lamp shade or dismantling the top panel.
The diagnostic process is as follows:
- 🔹 Remove the regulator handle and unscrew the fastening screw (if any).
- 🔹 Carefully remove the housing thermostat, being careful not to damage the capillary tube.
- 🔹 Disconnect the wires, first remembering their location.
- 🔹 Set the multimeter to resistance measurement mode (Ohm).
⚠️ Attention: The capillary tube is very thin and fragile. If you pinch or puncture it, gas will escape and the thermostat will become unusable.
Attach the multimeter probes to the contacts. At room temperature, the circuit should be closed (the device will show zero or a value close to it). If you put the sensor in the freezer (after packing it in a moisture-proof bag), after a while the contacts should open and the device will show infinity.
☑️ Diagnostic checklist
If the sensor does not open when cooling, it means bellows system lost sealing or gas inside degraded. In this case, the unit cannot be repaired; a complete replacement is required.
Replacing the thermostat with your own hands
If diagnostics confirm a malfunction, you must install a new element. When purchasing, pay attention to the markings - they must match the original. Different manufacturers (for example Tam, K59, Ranco) may have different capillary tube lengths and temperature switching points.
Installation of a new device is carried out in the reverse order of dismantling. Pay special attention to fixing the sensing tube. It should fit snugly against the evaporator or chamber wall in the same place where the original part was attached. Special clamps or adhesive tapes are often used for fixation.
After assembling and connecting all the wires, turn on the refrigerator. Do not load products right away - let the system return to mode within 2-3 hours. If during this time the compressor turns off on its own, it means that the replacement was successful.
The influence of external factors on operation
Sometimes the thermostat is working, but the refrigerator does not work correctly due to external conditions. For example, if the unit is located too close to the battery or in direct sunlight, the sensor may “think” that the chamber is warmer than it actually is and cause the motor to work harder.
It is also worth considering that in models with a single evaporator and system No Frost, the thermostat often controls the temperature of the evaporator, not the air in camera. If the evaporator becomes coated with ice due to defrosting problems, the sensor will receive incorrect data.
Regular defrosting and cleaning of the drain holes helps maintain the correct operation of the entire system. Do not allow the formation of a thick ice crust on the back wall, as this distorts heat transfer and disrupts the thermostat settings.
Frequently asked questions (FAQ)
Is it possible to temporarily short-circuit the thermostat to make the refrigerator work?
Technically, you can connect the wires directly and the compressor will work. However, in this mode the refrigerator will freeze indefinitely until you turn it off manually. This will lead to deep freezing of food, icing of the chamber and possible failure of the compressor due to overheating. Use this method only for a short-term check of the motor's performance.
Why did the refrigerator begin to freeze less slowly after replacing the thermostat?
Perhaps the sensitive tube of the new sensor does not fit tightly to the surface of the evaporator or is installed in the wrong place. The reason may also be an incorrect setting of the temperature range of the new element. Check the tightness of the tube and try to adjust the screw under the seal (if there is one and you have the appropriate skills).
How often should the thermostat be changed?
This element does not have a strict expiration date. Under normal operating conditions, mechanical thermostats last 5-10 years or more. Replacement is required only when signs of malfunction appear: failure to turn on, constant operation or temperature incontinence.
What is the difference between the K59 and K50 thermostats?
These are popular models of Danfoss thermostats. The main difference is the temperature range and the length of the capillary tube. K59 is typically used for cold rooms (range -24 to +10°C) and K50 for freezers or single-compartment refrigerators. Installing an unsuitable model will lead to incorrect operation.
Can a thermostat affect the formation of ice?
Yes, if the thermostat contacts are “stuck” or it is set to too low a temperature, the compressor will run longer than necessary. This causes excessive freezing of moisture from the air, which settles on the walls in the form of a dense layer of ice or frost.