A sudden stop of the compressor or, conversely, its endless hum often indicates a failure in the temperature control system. It is thermostat (the thermostat) that is responsible for turning the motor on and off depending on the heating of the evaporator. If this sensor fails, the refrigerator stops maintaining the set mode, which can lead to spoilage of food or defrosting of the entire chamber.
Diagnostics of this unit does not always require calling a technician, since in many cases the check can be performed independently using a minimal set of tools. Understanding the operating principle of mechanical and electronic regulators will allow you to quickly identify the cause of the malfunction. In this article, we will analyze the main symptoms of a breakdown and a step-by-step algorithm of actions.
Before starting disassembly, you need to make sure that the problem lies precisely in the electrical control circuit, and not in a freon leak or a malfunction of the start relay. Often users confuse the symptoms, attributing compressor failure to the thermostat. Competent diagnostics will save time and money, allowing you to replace only the defective part, and not the entire unit.
Operating principle and types of thermostats
The main task of the thermostat is to open and close the electrical circuit of the compressor when certain temperature thresholds are reached. Classic models use mechanical principlebased on the expansion and compression of gas or liquid inside a bellows tube. When the temperature inside the chamber drops, the pressure in the tube decreases and the contacts open.
In more modern units, such as LG No Frost or Samsung Digital Inverterelectronic sensors (thermistors) can be used. Their work is based on changes in electrical resistance depending on the ambient temperature. Such devices transmit a signal to the main control unit, which already makes a decision to start the motor.
⚠️ Attention: Mechanical thermostats often have specific markings (for example, K59, TAM-133), which indicate the temperature range of operation. Installing an unsuitable model will result in the refrigerator not operating correctly.
Understanding the type of device you have is critical to choosing a test method. If for mechanics it is enough to ring contacts, then electronic components require measuring resistance and comparing readings with reference values. Incorrect diagnosis can lead to the purchase of unnecessary spare parts.
What is the difference between a capillary tube and an electronic sensor?
The capillary tube of a mechanical thermostat is filled with refrigerant and physically reacts to changes in gas volume. An electronic sensor is a semiconductor element that changes its electrical properties. The mechanics are more reliable in conditions of power surges, the electronics maintain the temperature more accurately.
Visual and audio signs of malfunction
The first signal of problems with the thermostat is the uncharacteristic behavior of the compressor. If the refrigerator motor runs continuously without turning off for hours, or, conversely, does not start at all when plugged in, this is a direct indication of a failure in the control circuit. In the first case, the contacts could “stick” in a closed state, in the second, they could open forever.
Pay attention to the temperature conditions inside the chambers. If the food in the freezer begins to melt, and in the refrigerator compartment, on the contrary, the water in the glasses freezes, then temperature adjustment it is broken. This often happens when the bellows tube has lost its tightness or has moved out of its place.
- 🔊 The compressor hums, but does not start, or clicks and immediately stalls.
- 🌡️ The temperature in the chambers does not correspond to the set temperature the value of the regulator knob.
- 💧 Excessive ice forms on the back wall of the refrigerator compartment, which was not there before.
- 🔌 When turning the regulator knob, there is no characteristic click (in mechanical models).
It is also worth inspecting the adjustment knob itself and the rod. If the handle rotates freely without resistance or, conversely, is jammed, the problem may be mechanical damage to the internals of the unit. In some cases, oxidation of contacts leads to sparking, which can be noticed when the back panel is removed.
Preparation for diagnostics and safety measures
Before starting any work on repairing household appliances, you must strictly follow the electrical safety rules. De-energizing device - this is the first and mandatory action. Do not attempt to remove covers or touch electrical contacts while the power cord is connected to the outlet.
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be a multimeter (tester), which allows you to measure resistance and check the integrity of the circuit. You may also need screwdrivers (Phillips and flathead), pliers and, possibly, a knife for stripping contacts.
☑️ Preparing to check the thermostat
It is important to ensure good lighting of the work area. The thermostat is often hidden inside plastic cases or behind decorative panels. Be careful not to damage the plastic latches, which become brittle over time. If the refrigerator model is complex, like Bosch or Siemens, it is better to photograph the wire connections in advance.
⚠️ Attention: In some models, access to the thermostat requires partial defrosting of the refrigerator if it is located inside the chamber behind the evaporator. Make sure there is no ice inside that interferes with access.
Removing the thermostat: step-by-step instructions
The location of the thermostat depends on the design of the refrigerator. In classic models (Atlant, Indesit) it is often located inside the refrigerator compartment, under a lampshade or in a separate plastic box. In modern systems No Frost sensors can be moved outside the chamber, closer to the compressor.
The removal process begins with dismantling the adjustment knob. Usually it is simply removed by hand or secured with a locking screw that needs to be unscrewed. After this, access to the rod and fastening elements of the thermostat housing opens. Carefully remove the housing, being careful not to sharply pull the capillary tube.
If the thermostat is mechanical, pay attention to the length and condition capillary tube. It should not have any creases or signs of damage. Electronic sensors are attached with clips or screws to the evaporator or air duct. Disconnect the terminal block, having first remembered or photographed the color marking of the wires.
In some cases, to completely remove the sensor, it is necessary to remove the back wall inside the chamber or even dismantle the entire evaporator. If you feel that you cannot cope with the amount of disassembly, it is better to stop at this stage and call a specialist so as not to break the tightness of the system.
Checking with a multimeter: measurements and analysis
The most reliable way to determine serviceability is to check the electrical resistance. Switch the multimeter to resistance (Ohm) or continuity measurement mode. If you have a mechanical thermostat, find the two main contacts going from the mains to the compressor.
At room temperature, the mechanical thermostat contacts are usually closed, and the device should show zero or close to it. If the screen shows one (infinite resistance), then the circuit is open and the thermostat is faulty. To check the opening, you can cool the sensitive element (place it in the freezer for 15-20 minutes) - the contacts should open.
For electronic thermistors, the technique is different. It is necessary to measure the resistance at different temperatures and compare it with a table of values for a specific model. A discrepancy between real readings and tabular data by more than 10-15% indicates the need for replacement.
The following is an indicative table of resistances for common types of thermistors used in refrigerators:
| Temperature (°C) | Resistance (kOhm) - Type 1 | Resistance (kOhm) - Type 2 | Status |
|---|---|---|---|
| +25°C | 5.0 - 6.0 | 10.0 - 11.0 | Normal |
| +10°C | 8.5 - 9.5 | 16.0 - 18.0 | Normal |
| 0°C | 12.0 - 13.0 | 22.0 - 24.0 | Normal |
| -10°C | 19.0 - 21.0 | 35.0 - 38.0 | Normal |
It is important to understand that the values in the table may vary depending on the sensor manufacturer (Nidec, Danfoss, Ariston). A critical sign of a breakdown is a complete absence of resistance (break) or zero resistance (short circuit) at any temperature.
Replacing and setting up a new thermostat
If diagnostics confirm a malfunction, you need to purchase a similar part. When choosing, pay attention not only to the appearance, but also to the markings. The numbers at the end of the marking (for example, L, R, S) indicate the length of the capillary tube and the temperature range of operation. Installing an unsuitable thermostat will result in the refrigerator freezing too little or too much.
The installation process is performed in reverse order. Carefully insert the capillary tube into the mounting hole, being careful not to bend it at an acute angle. Secure the thermostat housing and connect the wires according to the photographs taken earlier. Make sure that the terminals are tight and not loose.
After assembling and connecting the refrigerator to the network, adjustment may be required. For mechanical models, this is done by rotating the adjusting screw hidden under a seal or plastic plug. Turning clockwise usually increases the shutdown temperature (the refrigerator will turn off earlier), turning it clockwise lowers it.
⚠️ Attention: Do not immediately set the minimum temperature. Let the refrigerator operate in normal mode for 4-6 hours to stabilize the temperature background, and only then fine-tune.
If after replacement the problem does not disappear, the compressor itself, the start relay may be faulty, or there is a refrigerant leak. In such cases, a more in-depth professional diagnosis is required using a pressure manifold.
Frequently asked questions (FAQ)
Is it possible to temporarily close the thermostat contacts to make the refrigerator work?
Technically, it is possible to check the compressor for a short time, but leave the refrigerator with shorted thermostat absolutely not. The compressor will run continuously, which will lead to freezing of the evaporator, overload of the motor and eventual breakdown. Use this method only for diagnostics for 1-2 minutes.
Why does the new thermostat not click?
The absence of a click may mean that the temperature inside the chamber has not yet reached the threshold for the new sensor to operate. It is also possible that you purchased a model with a different temperature range. If there is no click after 40 minutes of operation and obvious cooling, check the correct connection and serviceability of the part itself.
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 (shocks during transportation) can shorten this period. Scheduled replacement is not required, change only when signs of malfunction appear.
Does contamination of the contacts affect the operation of the thermostat?
Yes, oxidation or carbon deposits on the contacts (contacts) increase resistance, which can cause sparking, heating and sticking. When replacing a thermostat, always check the condition of the terminal block and, if necessary, clean them.