Sudden defrosting of food in the main chamber or, conversely, turning vegetables into ice blocks often indicates a failure of the temperature control system. The central element of this system is thermostat (thermostat), which is responsible for turning the compressor on and off depending on the sensor readings. If the refrigerator stops turning off or operates with short cycles, most likely the problem lies in this particular unit.
Independent replacement of the part is possible, but requires care and compliance with safety precautions, since the work involves electrical components and refrigerant. Incorrect installation may damage the evaporator tubes or cause a short circuit. In this article, we will analyze in detail the stages of diagnostics, selection of a suitable spare part and the process of its correct installation in various types of refrigeration units.
Before starting work, it is necessary to completely de-energize the equipment. Important: a mechanical thermostat cannot be repaired, it can only be replaced with a similar one in parameters. We will look at the nuances of working with capillary tubes, electrical contacts and fastening methods so that you can perform a quality replacement and extend the life of household appliances.
Principle of operation and types of thermostats
A thermostat is a device that closes or opens the electrical circuit of the compressor depending on the temperature inside the chamber. Classic mechanical models use gas-filled system: the sensitive element (thermal cylinder) contains freon or an inert gas, which, when heated, expands and presses on the membrane, opening the contacts. Electronic analogs use thermistors that transmit data to the control board.
The main difference lies in the method of fastening and the length of the capillary tube. For two-chamber refrigerators, the length of the tube can vary from 0.7 to 2.5 meters, and for single-chamber refrigerators it can be shorter. They are also divided into models with and without a defrost signal. Incorrect selection of the length of the tube will lead to the fact that it will not reach the desired point or, on the contrary, will bend into a spiral, which will distort the readings.
- 🧊 Mechanical: reliable, repairable (partially), have an adjusting screw under the seal.
- 💻 Electronic: more accurate, controlled board, often have a built-in display or indicators.
- 📏 Difference in length: a critical parameter that determines whether the part will fit your evaporator.
It is important to understand that electronic thermostats are more difficult to diagnose without special equipment. If you have a modern refrigerator with a display, the failure may lie not in the sensor itself, but in the control module. In such cases, simply replacing the hardware may not solve the problem, and flashing or replacing the board will be required.
Fault diagnosis before replacement
Before buying a new part, you need to make sure that the problem is in the thermostat, and not in a freon leak or a compressor malfunction. The simplest way to check is the "method of elimination". If the compressor does not start at all, try closing the thermostat contacts directly (after turning off the power!). If, after turning on, the motor started working and the cold began to set in, it means that the thermostat “died.”
The second symptom is that the refrigerator does not turn off for days, freezing over with a huge “fur coat” on the back wall. This indicates that the contacts inside the regulator are stuck in the "on" position, and the system does not receive a signal that the desired temperature has been reached. In mechanical models, gently tapping the case sometimes helps, but this is a temporary measure.
⚠️ Attention: When checking the contacts with a multimeter, make sure that the probes do not touch each other or other metal parts to avoid a short circuit.
To accurately diagnose an electronic thermostat, testing the thermistor is often required. Its resistance should change with temperature changes. If the resistance remains unchanged or shows a break, the part requires replacement. Remember that systems No Frost sensors may have several sensors, and the failure of one of them blocks the operation of the entire system.
Necessary tools and preparation
For successful replacement, you will need a minimum set of tools that most home craftsmen will have. Care is key as space inside the refrigerator is limited and the capillary tube is very thin and fragile. Damage to the tube will lead to a refrigerant leak, which will require an expensive refill from a specialist.
You will need pliers, screwdrivers (Phillips and flathead), side cutters for cutting through plastic clamps and, possibly, electrical tape to insulate the connections. If you are replacing the thermostat on a model with an open capillary tube, have a soft rag ready to wipe where the tube enters the chamber.
☑️ Tools for replacement
Be sure to prepare the workplace. Make room in front of the refrigerator and provide good lighting. Defrost the unit in advance if there is food or ice left in it, since working with wet, live components is dangerous.
Removing the old thermostat
The removal process begins by disconnecting the device from the power supply. Never ignore this rule, even if you are only replacing plastic parts, since the thermostat is part of the compressor's electrical circuit. Remove the temperature control knob by pulling it towards you (sometimes it is held on a screw under a decorative plug).
Next you need to gain access to the mounting location. In most refrigerators (Indesit, Ariston, Stinol), the thermostat is located inside the chamber, under the light bulb or behind the decorative panel. In models Atlant or old ZIL it can be located outside, at the top of the case. Carefully unscrew the fastening screws and remove the protective cover.
The most crucial moment is removing the sensitive capillary tube from the evaporator. It can be secured with plastic latches or simply inserted into the technological hole. Do not pull the handset with force! It needs to be released smoothly, millimeter by millimeter, trying not to bend or break it. If the tube is taped to the evaporator, cut off the fastenings with side cutters.
- 🔌 Take a photo of the wire connection diagram before disconnecting so as not to mix up the contacts during installation.
- 🧊 Be careful with plastic at low temperatures - it becomes brittle and breaks easily.
- 📏 Measure the length of the old capillary tube to make sure it matches the new part.
After removing the tube, disconnect the wires from the contact group. Usually there are three or four of them, depending on the presence of a defrost warning lamp. Remember or write down which wire is connected where. Now the old thermostat can be completely removed from the refrigerator.
Installation and connection of a new device
Installation of the new thermostat is carried out in the reverse order of dismantling. Insert the capillary tube into the hole in the chamber to the same depth as the old model. If the new tube is longer, its remainder must be carefully rolled into a spiral inside the chamber or behind the back panel, without bending at an acute angle.
Connecting electrical wires requires special attention. Use a photo or diagram you took earlier. Wires are usually color coded, but don't rely on color alone as manufacturers may change standards. Securely fix the wires in the terminals or twist them and then heat-shrink them.
⚠️ Attention: Make sure that the capillary tube does not touch moving parts (if any) or sharp metal edges that could damage it when the compressor vibrates.
Fix the thermostat housing in its original place. Make sure the adjustment screw (if available) is in the middle position. Install decorative panels and control knob. Only after complete assembly can you plug in the refrigerator.
What to do if the new tube is too long?
If the capillary tube of the new thermostat is significantly longer than the old one, do not cut it under any circumstances! The excess length should be carefully placed in rings inside the refrigerator compartment, securing them with soft wire or adhesive tape in a safe place where they will not interfere with food or shelves. Trimming will break the tightness of the system and make the thermostat inoperative.
Setting up and checking the operation of the system
After turning on the refrigerator, let it run for several hours to reach normal operating conditions. Do not load the chamber with products at once, so as not to create unnecessary heat load. Check if the compressor switches off after reaching the set temperature. The normal operating cycle includes 10-20 minutes of work and 30-40 minutes of rest (depending on the load and ambient temperature).
If the refrigerator runs without interruption, the thermostat may not “feel” the cold. In mechanical models there is often an adjusting screw under the seal. Turning clockwise (usually) increases spring tension, causing the compressor to shut down at lower temperatures. You need to turn the screw literally a quarter turn, waiting for the cycle after each change.
Complies with the model
Short (not enough) or long (crumpled)
Changes with temperature
Break or constant value
| Parameter | Normal value | Symptom of malfunction |
|---|---|---|
| Temperature in the chamber | +2...+5 °C | Food freezes or spoils |
| Compressor operating time | 30-40% of the cycle | Works constantly or too rarely |
| Capillary tube length | ||
| Resistance (electronic) |
Check the tightness of the tube inlet. If warm air enters the chamber through the hole, ice will form on the evaporator in the wrong places. If necessary, seal the hole with sealant or plasticine (temporary solution).
Common mistakes when replacing yourself
One of the most common mistakes is ignoring the length of the capillary tube. Installing a shorter tube will result in the sensing element not being in the evaporator area and the refrigerator will not turn off. A tube that is too long, if laid incorrectly, can be pinched by a door or shelf.
Another mistake is poor contact of electrical connections. Oxidized or loose terminals lead to heating, sparking and eventual burnout of contacts. Always strip the ends of the wires before connecting and use reliable connection methods (soldering or quality terminals).
⚠️ Attention: It is strictly prohibited to use thermostats that are not intended for use with food products or at low temperatures, as the housing materials may become toxic or brittle.
Also Users often forget about grounding. If the thermostat body is metal, make sure that it does not come into contact with live parts without insulation, or that the grounding wire is connected correctly, if so provided by the design.
FAQ: Frequently Asked Questions
Is it possible to install a thermostat with a different marking?
Yes, if the basic parameters match: the length of the capillary tube, the temperature range, the type of fastening and the location of the contacts. The markings may differ between manufacturers (for example, TAM instead of K59), but they may be functionally identical. Always check the table of analogues.
Why does the refrigerator click but does not turn on after replacement?
This may indicate a malfunction of the compressor start relay or the motor itself. It is also possible that the new thermostat is defective or not connected correctly. Check the presence of voltage at the input to the thermostat and at the output from it at the moment when the compressor should operate.
Is it necessary to recharge the freon after replacing the thermostat?
No, if you did not damage the capillary tube and cooling system during dismantling. The thermostat is an electrical/mechanical regulator, it is not part of the refrigerant circuit (unless you pierced the tube with a tool).
How can you tell if the thermostat is lying?
Use an external thermometer, placing it in a glass of water in the center of the chamber. If the thermometer readings differ significantly (more than 3-4 degrees) from the installed regulator knob, and adjusting the screw does not help, then the sensor is not working correctly.
How long does a new thermostat last?
The average service life of a high-quality thermostat is 5-10 years. Electronic sensors may fail earlier due to power surges in the network, so it is recommended to use a stabilizer for expensive equipment.