A sudden stop of the compressor or, conversely, its continuous operation without shutting down often indicates a failure thermostat. It is this small device that is responsible for maintaining a given temperature inside the chambers, opening and closing the electrical circuit at the right time. If the refrigerator has stopped freezing or has begun to turn food into a block of ice, this is the unit that should be suspected first.
Before calling a technician or buying a new part, it makes sense to conduct independent diagnostics. To do this, you will only need a basic set of tools and multimeter. A correctly performed check will save a significant amount of money and time, since replacing a thermostat is one of the simplest procedures in repairing household appliances. In this article we will analyze the algorithm of actions in detail.
You should not ignore signs of malfunction, since prolonged operation of the compressor idling or its frequent starts can lead to more serious damage, including burning out of the motor windings. Timely diagnostics will help preserve the resource of the unit. Let's figure out how this mechanism works and what exactly needs to be measured.
Design and principle of operation of the thermostat
The thermostat is an electromechanical device in which the sensitive element is a sealed flask (bellows) filled with refrigerant. This bulb is connected to the contact group through a bellows tube and a lever mechanism. When the temperature changes, the gas in the flask expands or contracts, creating pressure that physically opens or closes contacts.
The design can be made in the form of a separate block with an adjustment handle or integrated into the electronic control board in modern models. In classic mechanical thermostats, such as Tam 133 or K 59, the key role is played by the freon pressure inside the bellows. It is transmitted to a moving contact, which, when a certain temperature is reached, opens the compressor power circuit.
It is important to understand that the thermostat does not respond directly to the temperature of the air in the chamber, but to the temperature of the evaporator or a special sensitive element that is attached to it. That is why the correct location capillary tube is critical for the correct operation of the entire refrigeration circuit.
⚠️ Attention: In some refrigerator models, the thermostat is combined with a defrost button. When diagnosing such devices, it is necessary to take into account the presence of an additional contact, which closes only when the button is pressed.
There are single-contact and two-contact relays. In the first case, when the circuit opens, the voltage supply to the compressor simply stops. In the second, the opening of the main circuit is accompanied by the closure of the control lamp circuit, signaling an increase in temperature. This is an important nuance when using a multimeter, since the presence of an extra contact can confuse an inexperienced technician. dialing multimeter, since the presence of an extra contact can confuse an inexperienced technician.
External signs of a thermostat malfunction
It is possible to determine that the thermostat has failed even before disassembly begins housing, paying attention to the behavior of the refrigerator. The symptoms may be diametrically opposed, but they all indicate a violation of the logic of work contact group. Below are the main signs that require immediate inspection.
- ❄️ The compressor operates continuously, without turning off for hours, while a “fur coat” forms in the refrigerator compartment or all the products are frozen - this indicates that the contacts are “stuck” in a closed state.
- 🔇 The refrigerator is silent and does not make any sounds of the engine operating, although the light is on and the temperature inside has clearly increased - most likely, the contacts have oxidized or broken and do not conduct current.
- 🔄 The unit turns on for a short time, runs for 1-2 minutes and turns off again, after which the pause lasts an unreasonably long time - this is a sign of loss of sensitivity of the bellows or gas leakage from capillary tube.
You should also pay attention to the adjustment handle. If it scrolls with unusual ease or, on the contrary, is jammed, this may indicate mechanical damage to the internal elements. In rare cases, sparking is observed inside the thermal relay housing, which can be heard as a quiet crackling sound at the moment of the intended switching switching.
⚠️ Attention: If the compressor hums, but does not start, and after a while there is a click and the humming stops, the problem may not be in the thermal relay, but in the starting relay or the engine itself. Do not rush to change the thermostat without a comprehensive check.
Sometimes users are faced with a situation where the refrigerator seems to be working, but the temperature in the chambers does not correspond to the one set on the regulator. For example, at minimum it freezes just as much as at maximum. This is a direct signal that adjustment mechanism has lost its functionality and requires replacement or repair.
Preparation for diagnostics and dismantling
Before picking up a multimeter, it is necessary to ensure the safety of the work. Any manipulations with the electrical components of the refrigerator require completely disconnecting the device from the network. Even briefly touching live parts can lead to serious consequences. First, unplug the power cord from socket.
Next you need to gain access to the thermostat. In most refrigerator models, such as Indesit, Atlant or Beko, it is located inside the refrigerator compartment. Often, to gain access, you need to remove the plastic cover that covers the ceiling light or the temperature control knob. In some cases, partial disassembly of the internal panel is required.
☑️ Preparation for checking the thermostat
After removing the decorative elements, you will see the thermostat itself with the wires suitable for it. Before disconnecting the wires, it is strongly recommended to take a photo or sketch the connection diagram. The colors of the wires may differ in different models, and an error during assembly can lead to a short circuit or incorrect operation of the control lamp. To dismantle the relay itself, you may need to unscrew the mounting screws or carefully remove it from the latches. Be careful with the capillary tube: it is very thin and easily damaged. If the tube bursts, the gas will escape and the thermostat will become unusable. Carefully remove the sensitive element from the mounting hole in the evaporator or warning lamp.
To dismantle the relay itself, you may need to unscrew the mounting screws or carefully remove it from the latches. Be careful with the capillary tube: it is very thin and easily damaged. If the tube bursts, the gas will escape and the thermostat will become unusable. Carefully remove the sensor element from the mounting hole in the evaporator or air duct.
Method of testing with a multimeter
The main tool for testing is a multimeter switched to the resistance (Ohm) or continuity measurement mode. Before starting measurements, make sure that the probes are working properly by connecting them to each other: the device should emit a sound signal or show zero. This guarantees the reliability of the results obtained when diagnosing the electrical circuit.
The verification process consists of measuring the resistance between the contacts of the thermal relay in its different states. Mechanical thermostats usually have two or three contacts. If there are three contacts, then one of them, as a rule, goes to the light bulb. We need to find a pair of contacts responsible for powering the compressor. Under normal conditions (at room temperature), these contacts should be open or closed depending on the type of relay, but most often at room temperature the circuit is open unless the sensor is artificially cooled.
However, a more accurate method is to test the response to temperature. Apply something cold to the sensitive element (bulb), for example, an ice pack, or, conversely, warm it in your hands. Ideally, you should hear a characteristic click, and the multimmeter reading should change from one (infinity) to zero or vice versa. This indicates that contact group is mobile and responds to changes.
Nuances of checking three-pin relays
If your thermal relay has three terminals, then two of them (usually the outer ones) are the compressor circuit, and middle - lamp circuit. Call extreme contacts. If there is a connection between the middle and extreme contacts under certain conditions, then the lamp will light up when the main circuit is opened.
If the multimeter shows “1” (open) regardless of the temperature and the position of the adjustment knob, it means the contacts are oxidized or burned out. If the device shows “0” (short circuit) constantly, even after strong heating or cooling, it means that the contacts are “stuck” to each other. In both cases thermostat is considered faulty and must be replaced.
Table of diagnostic results
It is convenient to use a table to systematize the data obtained. It will help you quickly compare the device readings with the condition of the part. Please note that the values may vary slightly depending on the specific model of the refrigerator and the type of installed relay.
| Thermal relay status | Multimeter readings | Reaction to temperature changes | Diagnosis |
|---|---|---|---|
| Cold (below threshold) | 0 Ohm (Sound) | Click, transition to 1 | Good |
| Warm (above threshold) | 1 (Open) | Click, go to 0 | Okay |
| Any | 1 (Break) | No reaction | Breakage of contacts |
| Any | 0 Ohm (Sound) | No reaction | Sticking contacts |
It is important to consider that some thermal relays have specific characteristics, for example, forced closure of contacts under certain conditions. Therefore, if the measurement results seem strange to you, you should check the technical documentation for the specific model refrigerator. Sometimes, to be completely sure, a dynamic check is required, with a gradual change in the temperature of the sensor.
It is also worth remembering about the error of the device. If the resistance does not show exactly zero, but, say, 2-5 ohms, this may indicate burnt contacts. Such a relay may still work, but its resource is already running out, and soon it will require replacement. It’s better not to risk it and install a new part.
Replacement and setting up a new thermostat
If diagnostics confirm a malfunction, the thermostat must be replaced. The new device must have similar markings or be completely identical in parameters. Installation is carried out in the reverse order of dismantling. Carefully insert the capillary tube into the seat, being careful not to damage it, and fix housing the relay.
Connect the wires according to the diagram or photograph made earlier. Make sure the contacts fit snugly into their sockets and do not move loose. After assembling the case and connecting the refrigerator to the network, let it work. The initial startup may take some time, as the system needs to get into operating mode.
After replacement, it is recommended to conduct a test operation cycle. Load the chambers with food or containers of water and monitor the temperature throughout the day. If the refrigerator turns off and on at normal intervals, and the temperature corresponds to the set one, it means repair it was successful.
⚠️ Attention: Do not immediately set the thermostat knob to the maximum value (maximum cold). This can lead to continuous operation of the compressor and overheating, especially if the chambers are still warm. Start with average values.
In rare cases, after replacement, additional adjustment is required with a screw on the thermostat housing, which is hidden under a seal. However, for domestic purposes, the factory settings of analogues are usually sufficient. If you are not confident in your abilities, it is better to entrust the final adjustment to a specialist.
Frequently asked questions (FAQ)
Is it possible to temporarily close the contacts of the thermal relay so that the refrigerator starts working?
Technically, you can close the wires and the compressor will start working. However, in this case, it will run continuously until you manually turn it off. This is permissible only as a short-term measure to defrost or save food, but constant operation in this mode will quickly damage the compressor due to overheating and lack of rest cycles rest.
Why does the multimeter show resistance, but the refrigerator does not turn on?
If the circuit rings, but there is no start, the problem may be in other components: the start relay, the compressor itself or wiring. It is also possible that the thermal relay closes the circuit, but does not open it when heated, which is why the operating cycle is disrupted. A deeper electrical circuit is required. diagnosis electrical circuit.
How to distinguish an electronic thermostat from a mechanical one?
A mechanical thermostat has a capillary tube with a bulb and a handle with numbers. Electronic is a board with a sensor (thermistor), which is connected through a connector. Electronic sensors are checked not by continuity, but by measuring resistance depending on temperature, which should change smoothly, according to calibration table.
Is it necessary to defrost the refrigerator before replacing the thermostat?
Full defrosting is not always necessary if access to the thermostat is at the top chamber and does not require removal of the rear wall of the evaporator. However, if for access you need to bend the plastic or work near ice, it is better to defrost the unit so that water does not get on electrical contacts.