The situation when the refrigerator suddenly stops freezing often takes you by surprise, and the sound of a compressor running without stopping or, on the contrary, deathly silence can frighten any owner. One of the first steps in troubleshooting a technician is often called checking the thermostat, which requires temporarily excluding it from the electrical circuit. Bypassing the thermostat is a technical technique that allows you to apply voltage directly to the engine starting relay, bypassing the temperature sensor, in order to understand whether the compressor itself is alive and whether the wiring is working properly.
It is important to immediately indicate that this method is exclusively diagnostic and temporary. It is strictly forbidden to leave the refrigerator operating with a bypassed thermostat, as this will lead to uncontrolled cooling, freezing of food and possible failure of the compressor itself due to operation in abnormal mode. In this article we will analyze in detail why they do this, what tools are required and how to safely carry out the procedure without harming the equipment and yourself.
Before climbing inside the case, you need to clearly understand the design of the control system. Thermostat (or thermostat) is a switch that opens the circuit when the temperature inside the chamber is reached set temperature. If it is faulty and does not “see” heat, the circuit does not close and the engine does not start. It is to test this hypothesis that the method of artificial closure of contacts is used.
Principle of operation and symptoms of thermostat malfunction
A standard mechanical thermostat is a sealed system filled with a temperature-sensitive gas or liquid. As the temperature inside the refrigerator compartment changes, the pressure in the capillary tube changes, affecting a membrane that physically opens or closes electrical contacts. When this mechanism breaks down, the refrigerator is either silent or hums without interruption. It is critically important to distinguish a thermostat breakdown from a malfunction of the start relay or the compressor motor itself.
The main signs that it has failed include a lack of response to turning the temperature control knob. If you turn the knob from minimum to maximum, but you cannot hear a characteristic click, and the compressor is silent, this is the first bell. It is also worth paying attention to the condition of the products: if they began to melt, although the motor seems to be running jerkily, or, conversely, everything has turned into an ice block due to continuous operation. thermal sensor has failed, include no response to turning the temperature control knob. If you turn the knob from minimum to maximum, but you cannot hear a characteristic click, and the compressor is silent, this is the first bell. It is also worth paying attention to the condition of the products: if they have begun to melt, although the motor seems to be running jerkily, or, conversely, everything has turned into a block of ice due to continuous operation.
Electronic control systems use thermistors that change their resistance depending on the temperature. Checking them using the bridging method is impossible in the classical sense, since the control unit expects a certain resistance. An attempt to close the contacts on the electronic board may lead to a short circuit and burning of the control module.
⚠️ Attention: Do not attempt diagnostics if you are not confident in your abilities. Incorrect handling of electrical components can lead to electric shock or permanent breakdown of expensive equipment.
Necessary tools and safety measures
To carry out high-quality diagnostics, you do not need the arsenal of a professional electrician, but a basic set of tools is required. First of all, you need an indicator screwdriver or a multimeter to check the presence of voltage. Without these devices, you are acting blindly, which is unacceptable when repairing household appliances. You will also need pliers, side cutters and, possibly, electrical tape to insulate the connections.
Pay special attention to preparing the workplace. The refrigerator must be moved away from the wall, allowing access to the rear and, if necessary, to the interior panels. The floor must be dry and the lighting must be sufficient to distinguish wire colors and contact markings. A wet floor or poor light significantly increases the risk of accidents.
☑️ Preparation for diagnostics
When working, use only tools with insulated handles. If you plan to test a live circuit (which is highly inadvisable to do without experience), make sure your hands are dry and your shoes have non-conductive soles. Safety is priority number one, no diagnosis is worth the risk to your health.
Which wires should not be touched?
Never short the ground wires (usually yellow-green color) with phase or neutral. This will cause a short circuit and may result in fire or electric shock. Also be careful with the wires going to the light bulb if they are in close proximity.
Finding and accessing the thermostat
The location of the thermostat depends on the model and year of manufacture of your refrigerator. In older models, such as Atlant or Biryusa, it is often located inside the refrigeration chamber, in a plastic case where the capillary tube goes. To get to the contacts, you will have to remove the regulator handle and unscrew the fastening screws, then carefully remove the entire assembly.
In more modern models, the thermostat can be hidden behind the top panel (shade) inside the chamber or even placed outside, in a niche above the door or on the back wall of the case. In two-chamber refrigerators with a No Frost system, the thermostat is often responsible only for the refrigerator compartment, and in the freezer there is a separate defrost sensor. It is important not to confuse them when diagnosing.
After dismantling the plastic covers, the electrical part of the device will appear in front of you. This is usually a box with several wires going into it. The number of wires can vary from two to four, depending on the functionality (presence of a lamp, alarm, etc.).
| Refrigerator type | Thermostat location | Difficulty of access | Features |
|---|---|---|---|
| Single chamber (old) | Inside the chamber, left or top | Low | Simple design, 2-3 wires |
| Double chamber (Atlant) | Inside the refrigerator compartment | Medium | You need to remove the ceiling |
| Modern (Indesit, LG) | Behind the top panel or outside | High | Many fasteners, fragile plastic |
| Built-in | Often outside, in the base or on top | High | Required dismantling the facade |
⚠️ Attention: The plastic fastening elements inside the chamber become very fragile in the cold. Act carefully so as not to break the latches when dismantling the panels.
Technology for bridging contacts for testing
The bridging process itself consists of creating an artificial contact between the input wire (phase) and the output wire going to the compressor. A classic mechanical thermostat usually has three contacts: one for phase, one for compressor and one for lamp (or ground). We need to connect the phase to the compressor contact.
To do this, you can use a small piece of insulated wire with stripped ends or just a reliable metal object if you are confident in insulating your hands. Insert one end of the jumper into the terminal where the power comes in, and the other end into the terminal that goes to the compressor relay. If the thermostat is working, but simply does not work due to the cold, a clicking sound is heard. If it burns out, there is silence.
After installing the jumper, turn on the refrigerator. If the compressor starts and hums, it means that the circuit to the motor is intact, the starting relay and the motor itself are most likely in good order, and the problem is precisely in thermostat. If the relay clicks, the motor jerks and turns off, or there is silence, the problem is deeper (starting relay, motor windings or wiring).
The compressor will work until you unplug the plug from the socket or remove the jumper. Therefore, the duration of such a test should not exceed 2-3 minutes, so as not to overheat the motor and freeze the food.
Analysis of results and diagnostics of other components
If, after bridging the thermostat the compressor does not start, this does not always mean the death of the motor. The starting relay, which is located in a black or gray box on the compressor itself, may be faulty. It could stick or burn. It is also worth checking the integrity of the wires going from the thermostat to the relay for breaks or oxidation of the contacts.
If the motor hums but does not start, and after a few seconds the shutdown click is heard, there is likely a problem with the starting winding or mechanical jamming of the compressor. Attempts to “reanimate” it with a hammer or additional capacitors at home often lead to the final failure of the unit.
If the motor starts and runs smoothly, but the refrigerator does not freeze, the problem may be a freon leak or a clogged capillary system. In this case, the thermostat jumper helped eliminate the electrical part, but pointed to the refrigeration circuit, the repair of which requires a specialist with a vacuum pump and a charging station.
Why is it humming, but not freezing?
If the compressor is working, but there is no cold, check the condenser (grid on the back). If it is cold, and the tubes of the compressor also do not heat up/cool, most likely all the freon has escaped through a microcrack.
Replacement of the thermostat and final assembly
After confirming that the thermostat is faulty, it must be replaced. When purchasing a new part, pay attention to the markings: it must match the original or be a universal analogue with suitable temperature ranges. For example, different types of sensors are used for single-chamber and double-chamber refrigerators.
The installation process is the reverse of dismantling. Carefully insert the capillary tube of the new thermostat into the seat, without bending it sharply (this may break the tightness of the system). Connect the wires according to the color code or diagram, which is best photographed before disassembling. Securely fasten the device body.
After assembly, turn on the refrigerator and set the control knob to the middle position. After 20-30 minutes, check whether the compressor cycles on and off. If there is a cycle and cold appears, the repair was successful. If not, more in-depth diagnostics will be required.
Is it possible to leave the jumper instead of the thermostat?
Absolutely not. The jumper causes the compressor to run continuously. This will lead to freezing of the evaporator, food spoilage, compressor overload and eventual motor combustion or fire. The jumper is only for a test for 1-2 minutes.
How to check the thermostat with a multimeter without a jumper?
You need to remove the thermostat, immerse its sensitive part in warm water (about 30-40°C) for a couple of minutes. Then test the contacts with a multimeter in resistance measurement mode. There should be a “squeak” (short circuit). If you put it in the cold, it opens. If there is no reaction, the part is faulty.
Why doesn’t the new thermostat click?
Some modern thermostats operate silently or have a very quiet click. It is also possible that the new sensor has not yet reached the temperature to trigger. Let the refrigerator run for 30-40 minutes before checking.
Where to buy an original thermostat?
It is better to look for original spare parts in specialized stores for repairing household appliances, indicating the exact model of the refrigerator. Universal analogues (for example, TAM, K59) are often suitable, but require selection according to the length of the capillary tube and temperature conditions.