A sudden breakdown of refrigeration equipment often takes you by surprise, turning into a real household disaster. If the compressor stops starting or, on the contrary, works non-stop, the first one to come under suspicion thermostat. It is this small unit that is responsible for maintaining the specified temperature inside the chambers.
Before calling a technician or rushing to the store for a new part, it makes sense to conduct independent diagnostics. Checking the thermostat is a procedure that is accessible even to a person with minimal technical skills, if precautions are taken and the algorithm of actions is strictly followed.
In this article we will analyze the device of the element, typical symptoms of its failure and describe in detail the testing process using various methods. Thermal relay (or thermostat) is an electrical switch that opens or closes the compressor power circuit depending on the temperature of the evaporator or air in the chamber.
Signs of a malfunctioning thermostat
Understanding the symptoms allows you to localize the problem before opening the unit case. Thermostat can behave differently: sometimes it simply stops sending a signal to start motor, and in other cases “sticks” in a closed state, forcing the equipment to work for wear.
The most obvious sign is the complete absence of cold when the lighting is working and the socket is working. If you hear a click, but the compressor is silent, or the motor hums but does not start, the problem may lie in the lack of contact at the regulator terminals.
There is also the opposite situation, when the refrigerator freezes too much. The products in the main chamber are covered with an ice crust, and a fur coat grows on the back wall. This indicates that contacts the thermostats do not open, and the compressor operates continuously, ignoring the achievement of the desired temperature.
⚠️ Attention: If the refrigerator turns on and off too often (every 2-3 minutes), this may indicate not only a broken thermostat, but also for problems with the start relay or compressor. Do not rush to change parts at random.
It is also worth paying attention to the condition of the capillary tube if it goes directly into the chamber. There should be no traces of corrosion or mechanical damage on it, since leakage of freon from the bellows will make thermostat completely inoperable.
Preparation for diagnostics and safety measures
Any work related to the electrical components of the refrigerator requires strict adherence to safety precautions. The first and most important step is to completely disconnect the unit from the power supply. You cannot rely only on temperature regulators - you need to unplug the cord from the outlet.
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be multimeter (tester), configured for continuity testing or resistance measurement mode. Without this device, it will not be possible to carry out an accurate check, since a visual inspection often does not give results.
Additionally, prepare screwdrivers (Phillips and flathead) for removing the panels, as well as a container to collect melt water if defrosting is required. It is better to work in good lighting so as not to damage fragile plastic latches and wire insulation.
- 🔌 Multimeter with working probes and battery.
- 🔧 Set of screwdrivers of different sizes.
- 🧤 Dielectric gloves to protect hands.
- 🧊 A container and a rag to remove moisture.
Before getting to the thermostat itself, you often need to defrost the refrigerator. If there is a lot of ice inside the chambers, access to the units will be difficult, and moisture may get on the contacts, distorting the instrument readings. Leave the doors open for at least 2-3 hours.
☑️ Preparing for the test
Removal and visual inspection of the thermostat
The location of the thermostat depends on the model of the refrigerator. In modern units, it is often located inside the main chamber, hidden behind a plastic cover along with the lighting lamp. In older models, access may be from the outside, at the rear of the unit.
Carefully remove the decorative trim or casing. They are usually secured with snaps or a few screws. Your goal is to get to the place where the thermostat connects to the electrical wiring. You will see a plastic case with suitable wires and, possibly, a capillary tube coming out of it.
Carefully inspect the case for cracks, melting or signs of oxidation. If you find blackened plastic or melted terminals, this is a sure sign that a breakdown or overheating has occurred inside. In this case, repair is impossible - only replacement is required.
⚠️ Attention: The capillary tube of the thermostat is very thin and fragile. When dismantling, try not to bend it sharply or apply excessive force, so as not to break the tightness of the bellows.
Disconnect the wires from the thermal relay terminals. Before doing this, it is recommended to photograph the connection diagram or sketch out the color markings so as not to confuse the contacts during assembly. In different refrigerator models Indesit, Atlant or Stinol the color of the wires may differ.
Methods of checking with a multimeter
The most reliable diagnostic method is to use a tester. Switch the device to the resistance measurement mode (Ohm) or to the dialing mode with a sound signal. This will determine whether electric current is passing through the thermostat contacts.
At room temperature, the contacts of most thermostats should be closed. Touch the multimeter probes to the two main terminals (usually they are labeled 3 and 4, or are simply the main contacts). If the device beeps or shows zero (or a value close to zero), then the circuit is intact.
However, just a closed circuit is not enough. It is necessary to check the thermostat's response to temperature changes. To do this, you can immerse the sensitive part (bellows) in cold water with ice or, conversely, slightly heat it (if the design allows safe heating). When cooling, the contacts should open and the resistance should become infinite.
| Contact state | Multimeter readings | Diagnosis |
|---|---|---|
| Closed (when warm) | 0 Ohm / Sound | Normal |
| Open (when warm) | 1 (infinity) | Faulty (break) |
| Closed (at frost) | 0 Ohm / Sound | Faulty (sticking) |
| Breakdown to the body | Resistance between the terminal and the body | Danger / Replacement |
It is also important to check that there is no breakdown in the housing. Press one probe to any terminal, and the other to the metal body of the thermostat. The device should not respond. If there is resistance, then the insulation is broken, and the use of such an element is dangerous.
Direct connection and testing of the compressor
Sometimes it becomes necessary to exclude the thermostat itself from the circuit in order to make sure that the compressor and start relay are working properly. This is done by directly shorting the wires that went to the thermostat. This operation requires extreme caution.
Connect the wires suitable for the thermal relay directly to each other using an insulated jumper or simply twisting them (temporarily). Plug in the refrigerator. If the motor-compressor starts and works normally, then the problem is definitely in the thermostat.
If, with a direct connection, the compressor hums but does not start, or knocks out the circuit breaker, then the fault lies deeper - in the start relay, the motor itself or the wiring. In this case, replacing the thermostat will not solve the problem.
⚠️ Attention: Do not leave the refrigerator running with the thermostat shorted for a long time! This will lead to freezing of food and possible failure of the compressor due to continuous operation. Use this method only for short-term diagnostics.
After checking, be sure to open the circuit and unplug the unit before installing a new part. Working with electricity under load is unacceptable.
Why does the compressor not start even with a working thermostat?
The reason may be low voltage in the network, a faulty start relay, an interturn short circuit in the motor windings, or a jammed piston group. It is also worth checking the integrity of the supply wires.
Replacing the thermostat and setting
If the diagnostics confirmed a malfunction, you need to purchase a similar part. It is important to pay attention not only to the appearance, but also to the markings, the length of the capillary tube and the number of contacts. There are no universal solutions here; each model range requires a specific approach.
Installation is performed in the reverse order. Carefully secure the thermostat in its seat so that vibrations do not damage it. Pay special attention to fixing the sensitive tube - it should fit tightly to the evaporator or be in the area provided for by the design of the refrigerator.
After assembly and connection to the network, adjustment may be required. Many thermostats have screws on the body for adjusting the temperature range and differential (the difference between turning on and off). You should twist them carefully, making no more than half a turn at a time.
- ❄️ Make sure that the capillary tube is not pinched.
- 🔌 Check the reliability of all electrical connections.
- 🌡️ Let the refrigerator run a cycle before drawing conclusions about the quality cooling.
In some cases, especially when installing analogs instead of originals, the factory settings may not be enough. Then you need to call a specialist with equipment to accurately calibrate temperature conditions.
Is it possible to repair the thermostat yourself?
In most cases, thermostats are non-removable or their repair is not economically feasible. Attempts to disassemble a sealed bellows often lead to final failure. It’s easier and more reliable to buy a new element.
How often should you change the thermostat?
The service life of a high-quality thermostat is 5-10 years or more. Frequent replacements may indicate problems with the electrical network (voltage surges) or improper operation of the refrigerator.
Why does the new thermostat not turn off the refrigerator?
You may have purchased a model with a different temperature range or installed the capillary tube incorrectly. Also, the cause may be a freon leak in the cooling system, due to which the temperature does not reach the shutdown threshold.
Where can I find the thermostat markings?
The part number is usually marked on the metal body or plastic head of the thermostat. Look for combinations of letters and numbers, for example, TAM-133, K-59, Ranco, etc. This will help you find an exact analogue.