Sudden defrosting of food or, conversely, the formation of an ice crust on the walls of the chamber often indicates There is a malfunction in the temperature control system. The central element of this system is thermostat, which controls the cycles of switching on and off the compressor. If this unit fails, the refrigerator ceases to maintain the set mode, which can lead to spoilage of supplies or engine failure.
Diagnostics of this component does not always require calling a technician, since a basic check can be performed independently using a minimal set of tools. However, before disassembling the unit, it is necessary to clearly understand the principle of operation of the device and distinguish its failure from other faults, such as freon leaks or problems with the start relay.
In this article we will examine in detail methods for checking the integrity of the contacts, assessing the operation of the capillary tube and deciding whether replacement is necessary. Correct identification of the problem will save you time and money, allowing you to avoid purchasing unnecessary spare parts or, conversely, prevent a more serious breakdown due to ignoring symptoms.
Main signs of a malfunctioning thermostat
The first step in diagnosis is monitoring the behavior of the refrigeration unit. Thermostat (second The name of the thermostat) is responsible for opening the circuit when the desired temperature is reached and closing when it rises. If this mechanism jams, the compressor either works continuously, trying to cool the chamber to impossible values, or does not turn on at all.
The most striking symptom is the absence of characteristic pauses in the operation of the motor. In normal mode, the refrigerator turns on and off cyclically. If you hear that the engine is humming non-stop for hours, and a “snow coat” is forming inside the chamber even with minimal settings, this is a direct signal that the contacts are stuck in a closed state.
The opposite situation is also possible: the unit is silent, the products are flowing, and it is warm inside. This indicates that the thermostat contacts have oxidized or burnt out and the circuit is not closing to start the compressor. Sometimes you can hear a quiet click, but the engine does not start.
⚠️ Attention: If the refrigerator makes a loud crackling or humming sound immediately after trying to turn on, but quickly goes silent, the problem may not be in the thermostat, but in the start relay or the compressor itself. Don't rush to change the sensor until you rule out these options.
It is also important to pay attention to the temperature in different areas of the camera. If food freezes in the main compartment and the vegetable compartment is too warm, this may indicate incorrect calibration or displacement of the sensing element, although more often this is a sign of problems with the system No Frost or air flow distribution.
Preparation for diagnosis and safety precautions
Before proceeding with the physical test thermostat, it is necessary to ensure safe working conditions. Any manipulations with the electrical components of the refrigerator require completely disconnecting the device from the network. The residual voltage in the capacitors may be small, but the risk of electric shock or short circuit due to careless handling of the wires is real.
To carry out high-quality diagnostics, you will need a basic set of tools. First of all, you need screwdriver (often a cross or flat, depending on the refrigerator model) to remove the casings. The main testing tool will be multimeter, which allows you to measure resistance and check the integrity of the circuit.
You may also need a small container with warm water if you decide to test the sensitivity of the capillary tube “hot”. Don't forget to prepare a dry rag for wiping the contacts and insulating tape in case you need to temporarily insulate the wires.
☑️ Preparing to check the thermostat
Remember that working with refrigerant is prohibited without a license, but check the electrical part The thermostat is safe as long as the capillary tube itself is not damaged. If you see that the tube is pinched or has signs of corrosion, further operation cannot be carried out.
Visual inspection and access to the thermostat
The location of the thermostat depends on the model of the refrigerator. In most older and medium-sized models, it is located inside the refrigerator compartment, often built into the lampshade or located on the side wall. In modern units, the sensor can be hidden behind the control panel or moved outside.
To access the device, you usually need to remove the temperature control knob (if it is mechanical) and unscrew the screws securing the casing. Be careful with plastic latches - they can be fragile, especially on equipment that has been in use for many years. Plastic becomes brittle at low temperatures.
After removing the protective panel, you will see the thermostat itself. This is a box with wires suitable for it and a thin copper tube going deep into the housing or evaporator - capillary. Carefully inspect the device for external damage: melting, traces of burning, corrosion on the terminals or a violation of the tube seal.
| Visual sign | Possible cause | Actions |
|---|---|---|
| Fused contacts | Overcurrent, poor contact | Replacing the thermostat |
| Rust on the terminals | High humidity, condensation | Cleaning or replacement |
| Deformation of the capillary | Mechanical damage during installation | Replacement of the unit |
| Traces of oil on the tube | Depressurization of the system | Urgent repair at the master |
If there are no visual defects, we proceed to an instrumental check. Often the problem lies inside the mechanism, and from the outside the device looks absolutely fine.
Checking contacts with a multimeter (continuity test)
The most reliable way to check thermostat is to use a multimeter in the mode of measuring resistance (Ohm) or checking circuit integrity (audible signal). To do this, you need to disconnect the wires from the thermostat terminals. It is recommended to first take a photograph of the connection diagram so as not to confuse the contacts during assembly.
Take the multimeter probes and touch them to the input and output contacts of the thermostat. At room temperature, the contacts of most thermostats should be closed, and the device will show zero (or a value close to zero) and make a squeaking sound. If the resistance is infinitely high, then the contacts are open, which at room temperature is a sign of a malfunction.
Next, you need to check the circuit opens. To do this, place the sensitive element (capillary with a cone) in a container with warm water (about 30-40 degrees) for several minutes. After heating, the contacts should separate, and the multimeter should show one (open). If this does not happen, the thermostat is “stuck.”
Some models of thermostats have a third contact for connecting a lamp indicating the operation of the compressor. It's also worth checking out. Typically it opens when the compressor is running and closes when the motor stops. The logic of operation depends on the specific circuit, but lack of response to temperature is a sure sign of a defect.
⚠️ Attention: When taking measurements, make sure that your hands and multimeter probes are dry. Moisture on the contacts can distort the readings of the device or lead to a false conclusion about the serviceability of the part.
Analysis of the operation of the capillary tube
The key element of the thermostat is capillary tube, filled with refrigerant (freon). It is the expansion and compression of the gas inside this tube under the influence of temperature that moves the membrane that opens the contacts. If the tube has lost its tightness, the gas has evaporated, and the thermostat stops responding to temperature changes.
Checking the tightness visually is difficult, but you can indirectly assess the operation of the system. If, when placing the cone in warm water, a click does not open the contacts within 5-10 minutes, most likely the freon has left the capillary. Also, the copper tube should not show any traces of oil or black deposits, which often indicate a leak.
It is important not to kink the capillary tube when dismantling or checking. Mechanical damage to thin copper will lead to instant depressurization. If you notice that the tube is loose and not secured in its normal place on the evaporator, this may lead to incorrect temperature readings.
Why can’t you heat the thermostat with an open fire?
Using a lighter or torch to check the thermostat is strictly prohibited. Sudden and uneven heating can lead to an explosion of the gas flask or irreversible deformation of the membrane, which will permanently damage the part. Use only warm water.
In some cases, the capillary may simply be displaced from its place. If it does not fit tightly to the evaporator, the sensor will “think” that the chamber is warmer than it actually is, and will often turn off the compressor, not allowing the products to cool properly.
Specifics of checking electronic thermostats
In modern refrigerators with a system No Frost and digital control, the mechanical thermostat is replaced by an electronic sensor (thermistor). The principle of testing them is different: they do not make clicks, but change their electrical resistance depending on the temperature.
To check such an element, the multimeter is also set to resistance measurement mode. When the temperature of the sensor changes (for example, if you hold it in your fingers or lower it into water), the readings on the device screen should change smoothly. If the resistance remains unchanged or shows an open/short circuit, the sensor is faulty.
Electronic control modules are more sensitive to voltage surges. Often a thermistor failure is accompanied by an error on the refrigerator display. Error codes vary from manufacturer to manufacturer, so for accurate diagnosis you should refer to the technical documentation of the specific model.
It is worth noting that electronic sensors are less likely to fail spontaneously; more often the problem lies in oxidation of the contacts in the connector or a break in the wiring going to the sensor. Carefully inspect the wiring harness along its entire length.
Replacing the thermostat: when repair is impossible
If the check shows that the contacts do not close/open and the capillary tube is intact, or if a freon leak is detected from the thermostat bulb, the part must only be replaced. Repairing the internal mechanical parts of a thermostat at home is not possible due to the need for precise calibration and tightness.
When purchasing a new spare part, it is critical to know the exact markings of the old thermostat. Even outwardly similar models may have different capillary tube lengths, on/off temperatures, and contact types. Installing an unsuitable analogue will lead to incorrect operation of the refrigerator.
The replacement process involves disconnecting the wires, dismantling the old unit, installing a new thermostat in the seat and connecting the wires according to a previously made diagram or photograph. Pay special attention to the installation of the capillary tube - it must be fixed in the same position as the old one in order to correctly read the temperature.
After assembling and connecting the refrigerator to the network, it is recommended not to load it with food immediately. Allow the unit to return to operating mode for several hours to ensure that the new on and off cycles are normal.
Frequently asked questions (FAQ)
Is it possible to temporarily close the thermostat contacts to make the refrigerator work?
Yes, this can be done to briefly check the operation of the compressor or defrosting the system if the compressor does not turn on. However, leave the refrigerator with a shorted thermostat for a long time absolutely not. This will lead to continuous operation of the motor, freezing of the evaporator and possible failure of the compressor due to overheating.
Why does the new thermostat not click?
Some modern thermostats operate silently or make a very quiet click that hard to hear. If the multimeter shows a change in resistance or an open circuit with a change in temperature, then the part is working, even if there is no sound. Also, the absence of a click may be due to the fact that the ambient temperature has not yet reached the response threshold.
Where can I find the thermostat markings?
The markings are usually applied to the metal or plastic body of the device. To see it, you often need to remove the protective cover or lampshade. Look for a set of numbers and letters (for example, K59, TAM133), which will need to be reported to the spare parts seller.
Does the length of the capillary tube affect the operation?
Yes, the length matters. If the tube is too short, the sensing element will not reach the desired zone of the evaporator, and the refrigerator will not cool the food. If it is too long, the tube will have to be rolled up, which may disrupt heat transfer. It is best to use the original length or a universal one with a margin, carefully storing the excess.
How often should you change the thermostat?
The service life of the thermostat is usually 10 years or more. No scheduled replacement required. It should be changed only if obvious signs of a malfunction appear: refusal to turn on/off or incorrect temperature maintenance.