The situation when the refrigerator stops freezing or, conversely, turns food into an ice block often indicates a malfunction of the temperature control system. The central element of this system is a thermostat (thermostat), which is responsible for turning the compressor on and off depending on the temperature inside the chambers. If this sensor fails, the compressor either works continuously, trying to achieve non-existent cold, or does not start at all, leaving the food warm.
Before calling a technician or buying new equipment, it makes sense to do it yourself. Understanding how this unit works and what signs indicate its failure will save you a significant amount. In this article we will look at how primary diagnostics on your own. Understanding how this unit works and what signs indicate its failure will save you a significant amount. In this article we will look at how check the thermostat using a multimeter and other available methods, and also look at typical mistakes that inexperienced technicians make during repairs.
It is important to understand that the thermostat is an electromechanical device, and its resource is not endless. Over time, the contacts oxidize, the bellows tube loses its tightness, and the internal spring weakens. A critical sign of a malfunction is the absence of a characteristic click when turning the regulator knob, when the compressor is silent, although there is voltage in the network yes. If you notice such symptoms, further operation of the equipment without checking can lead to overheating of the motor or spoilage of products.
The principle of operation of the thermostat and signs of malfunction
The thermostat is a device that responds to changes in ambient temperature. Inside the housing is a sealed bellows tube filled with gas or liquid, which expands when heated and contracts when cooled. These pressure fluctuations are transmitted to the electrical contact switching mechanism. When the temperature in the chamber rises above the set point, the contacts close, starting the compressor. When the required cold is reached, the circuit opens.
It is possible to determine what checking the refrigerator thermostat is really necessary by a number of indirect signs. Users often confuse sensor failure with a freon leak or a faulty start relay. However, if the compressor hums, but does not start, or works without stopping, in 70% of cases the problem lies precisely in the temperature control circuit.
- ❄️ The compressor runs continuously, without turning off for hours, even if the chamber is already very cold.
- 🔇 The refrigerator motor is silent, although the light is on and you can hear the refrigerant flowing (no click on the switch).
- 🌡️ The temperature in the main chamber or freezer does not correspond to the set value on the regulator.
- 💧 The appearance of "snow" fur coats" on the back wall or, conversely, the complete absence of frost when the engine is running.
It is worth noting that in modern models with electronic control, the role of a mechanical thermostat is played by thermal sensor (thermistor). It is checked differently, but the symptoms of failure are similar. If you have an old refrigerator with a mechanical adjustment knob, then the methods described above will be most relevant. In the case of electronics, resistance testing will be required, rather than contact closure.
⚠️ Attention: If the compressor operates without stopping for more than 24 hours, this can lead to its thermal burnout. If such a symptom is detected, immediately disconnect the device from the network and carry out diagnostics.
Diagnostics should begin with a visual inspection and analysis of the behavior of the equipment. If the refrigerator turns on, runs for a while, turns off, but the temperature does not drop, the problem may not be with the thermostat, but with a refrigerant leak. But if the on-off cycle is fundamentally disrupted (either eternal work or complete rest), then checking the thermostat becomes a priority.
Preparation for diagnostics: tools and safety
Before start check the thermostat, it is necessary to ensure safe working conditions. Electricity and moisture are a dangerous combination, so all manipulations with the electrical part should be carried out only with the device disconnected from the network. You will need a minimum set of tools that any home craftsman can find in his home.
For high-quality diagnostics you will need:
- 🔧 Screwdriver (Phillips and flat) for removing panels and dismantling the unit.
- 🔌 A multimeter (tester) to check the continuity of the circuit and resistance.
- 🧊 A container with water and a thermometer (to check operation in different temperature conditions).
- 🔦 A flashlight for illuminating the interior of the chamber.
The preparation process also includes defrosting the refrigerator if a lot has accumulated in the chambers ice. This will not only make it easier to access the nodes, but will also allow you to more accurately evaluate the operation of the system after switching on. If you plan to remove the thermostat, make sure that you have free space to work near the refrigerator.
☑️ Preparing for diagnostics
It is important to determine the type of your thermostat in advance. Mechanical models have a long capillary tube that is inserted into the evaporator. Electronic sensors look like small plastic elements with wires. The method depends on the type of device, as Check the serviceability of the thermostat. For mechanical devices, a simple test is often sufficient, while electronic devices require resistance measurements at different temperatures.
Visual inspection and search for external defects
The first stage of diagnosis is a careful visual inspection. Often the cause of the malfunction lies not in the internal electronics, but in mechanical damage. Refrigerator thermostat - the device is sensitive, and any external influences can disrupt its operation.
First of all, inspect the capillary tube (if there is one). It should not have creases, cracks or signs of corrosion. If the tube is damaged, the fill gas evaporates and the device stops responding to temperature changes. Also check the condition of the adjustment knob: it should rotate with effort, but without jamming. If the handle rotates freely or, conversely, is jammed, this is a sure sign of internal failure.
Pay attention to where the thermostat is attached to the housing or evaporator. The fastening must be tight. If the assembly is loose or misaligned, it may not correctly read the air temperature in the chamber. In some models, the end of the capillary tube is attached with a special clothespin to the fins of the evaporator - check that it is in place.
⚠️ Attention: Never try to straighten a broken capillary tube by force. This is guaranteed to lead to its depressurization and the final failure of the unit.
If no visual defects are found, we proceed to a deeper check. Remember that oxidized contacts inside the thermostat itself are not visually visible, so the absence of external damage does not guarantee the serviceability of the device. Next, you will need to use measuring instruments.
Checking the thermostat with a multimeter: step-by-step instructions
The most accurate way check the refrigerator thermostat is to use a multimeter in continuity or resistance measurement mode. This method allows you to determine with a high degree of probability the integrity of the electrical circuit inside the device.
First you need to get to the thermostat contacts. Depending on the model of the refrigerator, it may be located:
- 📍 Inside the refrigerator compartment (usually under the lampshade or on the side wall).
- 📍 Outside, on the top of the case (in older models).
- 📍 In the niche above the refrigerator door cameras.
Remove the protective panel and carefully disconnect the wires from the thermostat terminals. Before doing this, it is advisable to photograph the connection diagram so as not to mix up the wires during assembly. Switch the multimeter to resistance (Ohm) or continuity measurement mode. Touch the probes to the thermostat contacts. If the device is working properly and is at room temperature, the circuit should be closed (resistance is close to zero, a beep sounds).
Now the most important test. Place the sensitive part of the thermostat (capillary tube or sensor) in a container of water at a temperature of about +5...+10°C (refrigerator temperature). After a few minutes, the contacts should open and the multimeter will show infinite resistance (open). If you put the sensor in ice water (around 0°C and below), the contacts of the mechanical thermostat may close again (depending on the type), but the electronic sensor will change resistance smoothly.
| Contact status | Multimeter readings | Diagnosis |
|---|---|---|
| Closed at any temperature | 0 Ohm (constant) | Contacts sticking (compressor does not turn off) |
| Open at any temperature | ∞ (infinity) | Open circuit (compressor does not turn on) |
| Changes during cooling/heating | 0 Ohm ↔ ∞ | Thermostat is working |
| Resistance jumps | Chaotic numbers | Unstable contact, requires replacement |
Nuances of checking electronic temperature sensors
Electronic thermostats (thermistors) do not click. Their serviceability is checked by measuring resistance at different temperatures and comparing them with a table of values for a specific model. Usually, as the temperature decreases, the resistance increases (NTC type) or falls (PTC type).
If the multimeter shows that the circuit does not break when cooling or does not close when heating, it means The thermostat is faulty it requires replacement. It is not economically feasible to repair this unit; it is easier and more reliable to install a new original or compatible analogue.
Elimination method: checking without instruments
What to do if you don’t have a multimeter at hand, but check the thermostat need it urgently? There is a method of elimination that allows you to indirectly diagnose the problem. It is based on temporarily closing the circuit bypassing the thermostat.
The essence of the method is as follows: you need to connect the wires going to the thermostat directly (using a jumper), excluding the regulator itself from the circuit. If after this the refrigerator compressor starts and starts (working normally), then the problem was in the thermostat. If the motor is silent even when directly connected to the network, you need to look for a fault in the starting relay, the compressor itself or the wiring.
It is important to be careful when using this method:
- ⚡ All work must be carried out only when the power is turned off.
- ⏱ Do not leave the refrigerator turned on with a jumper for a long time time (no more than 15-20 minutes), as it will work non-stop and may overheat.
- 🧤 Use an insulated tool to avoid electric shock.
This method is good for quick preliminary diagnostics, but it does not provide a 100% guarantee, especially if the thermostat is “buggy” and opens the circuit at the wrong temperature. Therefore, if possible, it is better to use a multimeter.
Replacing the thermostat: main steps
If the check confirms a malfunction, the only solution is replacement. The replacement process refrigerator thermostat requires care, especially when working with a capillary tube. The new unit should be as similar as possible to the old one (match the length of the tube, type of fastening and temperature range).
Sequence of actions for replacement:
- Disconnect the refrigerator from the power supply.
- Remove the old thermostat, having previously photographed the connection of the wires.
- Carefully remove the capillary tube from the evaporator (do not damage the walls of the tube!).
- Install the new thermostat by inserting the tube to the same depth as the old one.
- Connect the wires as done earlier diagram.
- Secure the case and turn on the refrigerator.
After replacement, you need to adjust the thermostat. Usually the handle is set to the middle position and the refrigerator is allowed to operate for several hours, monitoring the temperature in the chambers with a thermometer. If the temperature does not correspond to the norm, the adjustment is repeated.
⚠️ Attention: When installing a new thermostat, make sure that the capillary tube does not touch moving parts or sharp metal edges, otherwise it may fray over time.
Frequently asked questions and answers (FAQ)
Is it possible to repair the thermostat yourself?
At home, repairing the thermostat is practically impossible and impractical. The device is sealed, and damage to its integrity will result in loss of gas filler. In addition, calibration of springs and contacts requires special equipment. It’s easier and cheaper to buy a new part.
Why doesn’t the new thermostat click?
Some modern electronic thermostats operate silently. If you have a mechanical device, the absence of a click when turning the knob may indicate a defect or incorrect installation. Also, there may not be a click if the temperature inside the chamber has not yet reached the response threshold.
How often should you change the thermostat?
The service life of the thermostat is usually 5-10 years, but it can fail even earlier due to power surges or mechanical damage. No scheduled replacement is required, they are replaced only when signs of malfunction appear.
Does the temperature in the room affect the operation of the thermostat?
Yes, if the refrigerator is in a very cold room (below +10°C) or very hot, the thermostat may not work correctly. Most household models are designed to operate in climate class SN-T (from +10 to +43°C).