The situation when in the refrigerator the compressor suddenly stops turning on or, conversely, it works without stopping, is familiar to many owners of household appliances. Often the root of the problem lies not in the engine itself, but in the control system, namely thermostat or its electronic analogue. Understanding how to check a refrigerator thermostat allows you to save significant money on calling a technician if the breakdown really lies in this unit. Diagnostics does not require complex equipment, but it requires care and compliance with safety precautions.
The thermostat is a sensor that reads the temperature in the chamber and commands the compressor to turn on or off. If this mechanism fails, the refrigerator becomes either a non-functional drawer or a freezer that freezes food to the point of stone. In this article we will analyze all stages of diagnostics: from initial signs of a malfunction to professional testing of contacts with a multimeter. You will learn to distinguish a thermostat failure from problems with the start relay or freon leak.
Main signs of a thermostat failure
The first step in diagnosis is to observe the behavior of the unit. Symptoms may be obvious or indirect, but they always indicate a violation of the cooling cycle. If you notice that the equipment behaves uncharacteristically, you should take a closer look at the operation of the motor and the temperature inside the chambers.
One of the most obvious symptoms is that the compressor does not start at all, although the light is on and you can hear the buzzing of the network. In this case, thermostat may simply not close the circuit, considering that the temperature is normal, even if it is warm in the chamber. The opposite situation, when the motor hums continuously, trying to catch up with non-existent cold, also indicates sticking of the contacts in the “on” position.
There are a number of specific signs that help localize the problem in the temperature sensor:
- 🧊 In the refrigerator compartment, food begins to deteriorate or, conversely, freeze, although previously the operating mode was stable.
- 🔌 The compressor turns on extremely rarely, and the duration of its operation has been significantly reduced compared to the norm.
- ❄️ A “snow coat” or ice appears on the back wall of the main chamber, which indicates constant hypothermia.
- 🔊 The relay clicks when you try to start, but the engine is silent (although this may indicate other components).
⚠️ Attention: If the compressor hums, clicks, but does not start and turns off after a few seconds, the problem may be not only in the thermostat, but also in the starting relay or the motor windings. Do not change parts at random without first checking.
It is important to consider that in modern models with a system No Frost and electronic control, instead of a mechanical thermostat, a thermal sensor (thermistor) is often used. Checking it requires a slightly different approach, which we will discuss in the appropriate section. Mechanical regulators, equipped with a long capillary tube, are more often found in classic models.
Preparation for diagnostics and safety precautions
Before proceeding with disassembly and testing, it is necessary to prepare the workplace and tools. Safety is the number one priority as work will be carried out on an electrical appliance. Any carelessness can lead to electric shock or damage to the wiring.
First of all, the unit must be completely de-energized. Simply turning off the button is not enough - you need to unplug the plug from the socket. After this, you should defrost the chambers if ice has accumulated in them, and move the equipment away from the wall to provide access to the back panel. You will need a minimum set of tools: screwdrivers (Phillips and flat-head), pliers and, of course, multimeter to measure resistance.
The preparation process includes several mandatory steps:
- 🔌 Complete disconnection from the power supply and waiting 10-15 minutes to discharge the capacitors.
- 🧹 Freeing the internal space from products and shelves for ease of access.
- 🛠️ Preparing a bright flashlight, since it may be dark in the compressor niche or inside the chamber.
- 📸 Taking photographs of the wiring diagram in front of them disconnection so as not to mix up the contacts during assembly.
Pay special attention to the condition of the wire insulation. If you see melted insulation or burn marks on the terminals, this may indicate a short circuit, which led to the failure of the thermostat. In such cases, simply replacing the sensor may not solve the problem completely.
☑️ Safety check
Removing the thermostat in different models
The location of the thermostat depends on the design of the refrigerator. In older Samsung or Indesit models, it is often located inside the refrigerator compartment, and its adjustment knob protrudes onto the panel. In more modern versions, such as LG or Bosch, the sensor can be hidden behind the lampshade or built into the housing.
If the adjustment knob is inside, carefully remove the plastic lever and unscrew the screw holding the thermostat housing. Sometimes access requires removing the entire top panel of the camera. Be careful with the capillary tube - this is a thin copper or aluminum tube filled with freon. Damage to the tube will lead to refrigerant leakage and failure of the entire system.
In models with electronic control, temperature sensors are usually located:
- 📍 Behind the rear wall of the refrigerator compartment (in a plastic casing).
- 📍 In the evaporator area of the freezer (requires disassembling the No Frost system).
- 📍 In the cold air supply channel.
⚠️ Attention: The capillary tube of a mechanical thermostat is very fragile. Do not bend it or jerk it sharply. If the tube bursts, it will be impossible to restore the functionality of the refrigerator on your own without a vacuum pump and freon.
To remove the sensor, in some cases it is necessary to remove the decorative trim on the ceiling of the chamber. Fastenings can be with latches or screws. Act smoothly so as not to break the plastic fasteners, which become especially brittle in the cold.
Visual inspection and initial check
After removing the unit from the refrigerator body, first carry out a visual inspection. Look for traces of contact oxidation, soot, or mechanical damage to the housing. If plaque is visible on the terminals, it can be carefully cleaned, but most often this is only a symptom and not the cause.
Pay attention to the bellows (corrugated part) and the capillary tube. They should not have dents, cracks or signs of corrosion. If the tube is deformed, the pressure inside it has changed, and thermostat can no longer respond correctly to climatic temperature changes. In this case, the part must be unconditionally replaced.
The simplest test can be carried out without instruments, but it only works for mechanical models. Immerse the sensing part (capillary tube) in a container of water at room temperature and then in a container of ice. During sudden cooling, a characteristic click of the contacts opening should be heard. The absence of sound is a sure sign of a malfunction.
Is it possible to restore an old thermostat?
Inside the thermostat there is a sealed system with gas or liquid. If the seal is broken or the physical properties of the filler have changed, it cannot be restored. Repair is only possible if the contacts are oxidized, but this is a temporary measure. It is more reliable and safer to install a new part.
Checking with a multimeter: step-by-step instructions
The most accurate diagnostic method is to use a tester (multimeter). This device allows you to measure the resistance of a circuit and determine whether the contacts close when the temperature changes. To work, switch the multimeter to resistance measurement (Ohm) or continuity mode.
First, determine which contacts are responsible for the operation of the compressor. Usually there are two or three. If there are three contacts, then the third often goes to a light bulb or fan. Find a pair of contacts that should close at room temperature. Connect the multimeter probes to these contacts.
The test algorithm is as follows:
- Connect the multimeter probes to the thermostat contacts.
- At room temperature, the device should show a resistance close to zero (or emit a sound signal).
- Place the sensitive part of the sensor in the freezer or apply ice to it.
- After a few minutes, the resistance should go to infinity (open circuit), which means the contacts open.
If the circuit does not break during cooling (the arrow does not move or the numbers do not change), then contacts are stuck or the mechanism has failed. If the circuit does not close even in warm conditions, it means that the contacts are oxidized or broken. In both cases, replacement is required.
| Condition | Multimeter readings (heat) | Multimeter readings (cold) | Verdict |
|---|---|---|---|
| Good | 0 Ohm (Sound) | ∞ Ohm (No sound) | Works fine |
| Sticking | 0 Ohm (Sound) | 0 Ohm (Sound) | Faulty (replacement) |
| Broken contacts | ∞ Ohm (No sound) | ∞ Ohm (No sound) | Faulty (replacement) |
| Unstable contact | Jumping values | Jumping values | Faulty (replacement) |
Electronic sensors and thermistors
In modern refrigerators, mechanics have given way to electronics. Here, instead of a thermostat, thermistorsare used. Their operating principle is based on a change in electrical resistance depending on temperature, and not on mechanical opening of contacts. Checking such parts requires knowledge of their nominal values.
For diagnostics, it is necessary to know the resistance of the sensor at a certain temperature (usually at +25°C). This data can be found in the technical documentation for a specific model or in the correspondence tables for brands. A deviation from the nominal value of more than 10-15% indicates a malfunction.
The process of checking the electronic sensor:
- 🔍 Find the markings on the sensor body (for example, 5 kOhm, 10 kOhm).
- 🌡️ Measure the resistance at room temperature temperature and compare with the table.
- ❄️ Cool the sensor and watch for a smooth change in resistance.
- 📉 A sharp jump or lack of reaction indicates a breakdown.
⚠️ Attention: The characteristics of thermistors may differ even within the same model refrigerator. Always check the official data of the manufacturer or use a donor sensor from a working similar device.
A common problem with electronic sensors is oxidation of the contacts in the connector, and not the breakdown of the element itself. Therefore, before purchasing a new part, carefully clean the contacts and check the integrity of the wiring going to the control unit.
Replacing and setting up a new regulator
If the diagnostics confirm a malfunction, proceed with replacement. When purchasing a new part, pay attention not only to compatibility with the brand, but also to the length of the capillary tube and the type of fastening. Universal thermostats require adjustment to the location.
Install the new thermostat in the reverse order, being careful with the tube. Secure it in the same position as the old one using standard clips. Incorrect position of the sensitive element will lead to incorrect operation of the refrigerator.
After assembly and connection to the network, it may be required adjustment. Rotate the thermostat knob to achieve the desired temperature inside the chamber. Ideally, the operating cycle should be: 10-15 minutes of compressor operation and 20-30 minutes of rest. If the refrigerator operates in this mode, then you have completed the task successfully.
How often should the thermostat be changed?
Thermoregulator is a resource part, but not eternal. The average service life of a mechanical thermostat is 7-10 years. Electronic sensors may last longer, but they are more sensitive to power surges. Scheduled replacement is not required; they are changed only when signs of malfunction appear.
Why doesn’t the new thermostat click?
Some modern thermostats operate silently or have very quiet contact movements. If the refrigerator gains temperature and turns off, and then turns on again when it warms up, then the regulator is working, even if you don’t hear a click. The main criterion is maintaining the temperature.
Is it possible to temporarily bypass the thermostat?
Theoretically, you can close the contacts directly to start the compressor, but doing this is strictly not recommended for permanent operation. The refrigerator will freeze endlessly, which will lead to food spoilage, icing and rapid wear of the compressor. This is only an emergency measure to check.