Checking the thermostat of the Indesit No Frost refrigerator: instructions

Refrigerators Indesit s systems No Frost have earned a reputation as reliable equipment, but even they are not immune to component wear. One of the common reasons for temperature violations or the appearance of ice on the back wall is the failure of the thermostat. This small device is responsible for turning the compressor on and off depending on the temperature in the refrigerator compartment. If you notice that the unit is working without interruptions or, on the contrary, has stopped cooling the products, the first step is to diagnose this particular unit.

Before proceeding with disassembly and complex measurements, it is necessary to conduct a visual inspection and an initial assessment of the situation. Thermal relay (or thermostat) is an electromechanical or electronic sensor that opens the compressor power circuit when the set values are reached parameters. In models Indesit with electronic control, this function is often performed NTC sensor, and in older or budget versions a classic thermostat with a capillary tube is used. Understanding which type is installed in your case is critical for choosing a verification method.

In this article we will analyze in detail the algorithm of actions for both types of devices. You'll learn how to safely reach the sensor, what tools you'll need for diagnosis, and how to interpret multimeter readings. Self-checking will save time on calling a technician or immediately confirm the need to replace a part. Remember that any work with electrical components requires compliance with safety precautions, so follow the instructions carefully.

Symptoms of a malfunctioning thermostat in the No Frost system

Diagnostics always begins with an analysis of the symptoms. If thermostat fails, the refrigerator stops responding correctly to changes in internal temperature. In the system No Frost this can lead not only to food spoilage, but also to the formation of ice jams in the evaporator, since the defrost cycle may not start on time or, conversely, start too often.

Let's consider the main signs indicating a problem with the sensor:

• ❄️ The compressor works continuously, without turning off even when a low temperature is reached, which leads to freezing.
• 🔊 The unit does not turn on at all, although the indicators are on, and you can hear the hum of the network, but the engine does not start.
• 🌡️ The temperature in the chamber is much higher installed, the compressor turns on rarely and operates in very short cycles.
• 💧 A “fur coat” or ice forms on the back wall of the refrigerator compartment, although the system No Frost should prevent this.

⚠️ Attention: If the refrigerator makes clicking noises but does not start, the problem may be not only in the thermostat, but also in compressor start relay or the engine itself. Do not rush to change the sensor until you rule out other causes.

It is important to distinguish between mechanical and electronic failures. In mechanical thermostats, the capillary tube often depressurizes or the contacts stick. In electronic NTC sensors most often the resistance of the resistive element changes, which leads to the transmission of incorrect data to the control module. In both cases, the behavior of the refrigerator Indesit will be similar, but the testing methods are different.

Removing the thermostat: access to the sensor

To carry out high-quality diagnostics of the thermostat, it must be removed from the refrigerator body. In models Indesit No Frost the location of the sensor depends on the year of manufacture and the specific series. Most often, the thermostat is located inside the refrigerator compartment, hidden behind a plastic panel or built into the temperature control knob.

The dismantling process requires care so as not to damage the fragile plastic latches and wire insulation. Before starting work, be sure to disconnect the refrigerator from the power supply by removing the plug from the outlet. This is the first and main safety rule, neglect of which can lead to electric shock or short circuit.

Algorithm for removing the sensor:

• 🔌 Empty the refrigerator compartment of food and remove the shelves that interfere with access to the back or top wall.
• 🔧 Remove the decorative trim or lighting shade, under which the thermostat housing is often hidden.
• ✂️ Carefully disconnect the wires, having previously photographed the connection diagram so as not to confuse the contacts during assembly.
• 🌬️ If you have a model with a capillary tube, it is extremely carefully remove the sensitive tube from the evaporator, being careful not to bend or damage it.

In some modern models Indesit with electronic control, the temperature sensor can be located directly on the evaporator behind the back wall of the chamber, hidden by a plastic box. In this case, you will need to remove the back panel inside the refrigerator. Be careful: plastic becomes very fragile in the cold and can crack if handled carelessly.

Diagnostics of a mechanical thermostat with a multimeter

Mechanical thermostat is a device with a sealed capsule filled with freon or other gas-liquid agent, and electrical contacts. When the temperature changes, the pressure inside the capsule changes, which leads to the opening or closing of contacts. Checking such an element is carried out using a multimeter in resistance (Ohm) or continuity measurement mode.

First, remove the adjustment knobs and get to the sensor contacts. Mechanical thermostats Indesit usually have two or three terminals. If there are three pins, then the third one often serves to ground or indicate the operation of the compressor (light bulb), and it can be ignored when testing the main contacts. The main interest is in the two main contacts through which power is supplied to the compressor.

The procedure for checking a mechanical thermostat:

1. Set the multimeter in continuity or resistance measurement mode.
2. At room temperature, the contacts should be closed (resistance is close to 0 Ohm), if the regulator knob is set to maximum.
3. Place the sensitive tube of the sensor in a container with cold water (temperature about 0...+5°C) or attach a cold object to it.
4. When cooling, a click should be heard, and the resistance between the contacts should become infinite (open circuit).

If during cooling there is no break in the circuit, or if the contacts do not close when heated, the thermostat is considered faulty and requires replacement. Also a sign of a malfunction is a breakdown on the case: if the multimeter shows resistance between any contact and the metal body of the sensor, it cannot be used - it is dangerous.

Why is a click important?

A click indicates mechanical movement of the bimetallic plate inside the device. If there is no click, but the resistance changes smoothly, this may indicate degradation of the contacts, but most often such a device will no longer be able to correctly control the compressor over a wide temperature range.

Checking the electronic NTC temperature sensor

In refrigerators Indesit recent years of production, instead of mechanical “tablets”, electronic sensors based on thermistors (NTC). Their operating principle is based on a change in electrical resistance depending on the ambient temperature. The lower the temperature, the higher the resistance, and vice versa.

To check such a sensor you will also need a multimeter, but we will not evaluate the presence of a contact (break), but specific resistances. It is important to know that the resistance of different sensor manufacturers at a certain temperature may differ, however Indesit there are certain standard values.

Table of typical resistance values of NTC sensors at different temperatures:

To check the sensor, measure its resistance at room temperature and compare with the tabular data. Then cool it (for example, by placing it in a glass of water and ice) and measure again. The resistance should increase smoothly. If the multimeter shows zero (short circuit) or infinity (break) at any temperature, the sensor is faulty.

⚠️ Attention: Do not heat the electronic sensor with an open flame or a hairdryer at maximum power - a sudden temperature change can destroy the sensitive element. Use only natural cooling or moderate heating.

It often happens that visually the sensor is intact, the wires are not frayed, but its characteristics have “floated away”. In this case, the control module receives incorrect data and does not turn on the compressor or defrost system. Replacing such an element usually solves the problem.

Analysis of errors on the display and control module

Modern refrigerators Indesit are equipped with a self-diagnosis system. If the thermostat or temperature sensor fails, an error code may appear on the display or by flashing indicators. This greatly simplifies troubleshooting, as it indicates a specific problem unit.

The most common error codes associated with temperature sensors:

• 🚨 F03 — Malfunction of the evaporator temperature sensor (often associated with the No Frost system).
• 🚨 F04 — Problem with the refrigerator temperature sensor.
• 🚨 F05 — Faulty freezer temperature sensor.
• 🚨 F07 — Communication error between the control module and the user interface (may be caused by a break in the sensor cable).

If the corresponding code is lit on the screen, this does not always mean that the sensor itself is broken. The problem may lie in broken wires, oxidation of contacts in the connector, or a malfunction of the electronic module itself. Therefore, a visual inspection of the wiring and “continuity” of the circuit from the connector to the sensor are mandatory steps before purchasing a new part.

In some cases, resetting the refrigerator may be necessary to reset the error. To do this, disconnect the device from the network for 10-15 minutes. If after turning on the error appears again, it means that the malfunction is hardware in nature and requires replacement of the component.

Replacement of the thermal relay and final check of the system

Once the malfunction is confirmed, it is necessary to replace it. For mechanical thermostats, it is critical to select an analogue with identical parameters: capillary tube length, on/off temperature range and type of mounting. Using an unsuitable analogue will result in the refrigerator not operating correctly.

Install the new sensor in the reverse order. Make sure that the capillary tube of the mechanical thermostat or the body of the electronic sensor fits tightly to the temperature measurement location (evaporator or chamber wall). Poor thermal contact will lead to a delay in the system's response.

Final steps after replacement:

1. Carefully check all electrical connections, make sure that the wires are not dangling or touching moving parts or hot surfaces.
2. Plug in the refrigerator and set the control to the middle position temperature.
3. Listen to the start of the compressor: it should turn on after a while (or immediately if the chamber is warm) and work cyclically.
4. Let the refrigerator operate for several hours without loading food to make sure it reaches the mode and there are no errors.

⚠️ Attention: If after replacing the mechanical thermostat the compressor does not start, it may be a new sensor requires adjustment with a screw on the case (if there is one) or its parameters do not match the original. Do not leave the refrigerator unattended during the first hours of operation.

Timely diagnostics and replacement of the thermal relay can extend the life of the compressor and avoid defrosting the entire contents of the refrigerator. Regularly monitor the temperature conditions and respond to the slightest changes in the operation of the equipment.

Is it possible to temporarily short-circuit the thermostat contacts to make the refrigerator work?

Technically, this is possible, and the compressor will start working continuously. However, this is an extremely dangerous temporary measure. The refrigerator will stop turning off, which will lead to freezing of food, icing of the evaporator and, most importantly, to overload and combustion of the compressor. Use this method only for a short-term check of the engine's performance.

Why does the new thermostat click too often?

Frequent clicking (short cycle) may indicate that the sensor sensing element is not installed correctly. If it does not fit tightly to the cooled surface or, conversely, is too close to the heat source, the readings will fluctuate. Also, the reason may be that the parameters of the new thermostat do not correspond to the original.

How to distinguish the original thermostat from an analogue?

Original spare parts Indesit (often produced Danfoss, Klixon or Ranco) have clear markings, logos and neat assembly. The part number is always indicated on the original body. Analogues may differ in the quality of plastic, length of wires and calibration accuracy. When purchasing, pay attention to the country of origin and the availability of certificates.

Does the network voltage affect the operation of the thermostat?

Strong voltage surges can lead to burning of the contacts inside the thermostat, especially at the time of switching (on/off). If your network has unstable voltage, it is recommended to use a stabilizer or surge protector to protect the electronics and relays of the refrigerator.