The appearance of ice on the back wall of the freezer or a complete cessation of cooling in the refrigerator compartment often indicates a failure in system automatic defrost. In Hotpoint-Ariston models with No Frost technology, this problem most often lies in the failure of one of the evaporator components, and the defrost temperature sensor becomes the first candidate for testing. This small but critical element controls defrost cycles, preventing the formation of ice plugs that block the air channels.
If your refrigerator has stopped freezing, and a thick layer of ice is visible on the evaporator, it is necessary to diagnose the electrical circuit. Owners often confuse the defrost sensor with a fuse or heating element, but it is the thermistor (this is the technically correct name for this sensor) that sends a signal to the control module about the need to turn on the heating element. The malfunction of this component leads to the fact that the “brain” of the refrigerator either does not start defrosting at all, or, conversely, heats the evaporator for too long, which causes the compressor to overheat.
Before you start disassembling the unit and looking for a multimeter, it is important to make sure that the symptoms really indicate a problem with the sensor. In modern models Hotpoint-Ariston with electronic control, a malfunction is often accompanied by the appearance of an error code on the display or blinking indicators. However, even if there are no external signals, a mechanical resistance test is the most reliable way to identify a defect. In this article, we will analyze in detail the dismantling process, the testing method and the interpretation of the results obtained.
⚠️ Attention: Any work on diagnosing the internal components of the refrigerator should be carried out only after the device has been completely disconnected from the electrical network. Working under voltage is fatal and can lead to irreversible damage to the electronic control module.
Fault symptoms and the role of the thermistor in the No Frost system
The defrost sensor in Hotpoint-Ariston refrigerators is a thermistor with a negative temperature coefficient (NTC). This means that when the temperature decreases, its electrical resistance increases, and when heated, it decreases. The control module reads these changes and, when the resistance reaches a certain value (which corresponds to a temperature of about +5...+10°C on the evaporator), turns off the heater. If the sensor “lies” or shows a break, the defrosting cycle is disrupted.
The main sign of failure thermistor is the formation of so-called “sludge” or a dense block of ice around the fan and evaporator. Air stops circulating between the chambers, and although the freezer may continue to freeze locally, the temperature in the refrigerator compartment rises and food spoils. In some cases, the refrigerator may work in increased mode, trying to compensate for the lack of cold, which leads to increased noise and energy consumption.
Another symptom may be frequent turning on and off of the compressor or, conversely, its continuous operation without reaching the set temperature. It is important to understand that similar symptoms can be caused by fan or heating element malfunctions, so a comprehensive check of all elements of the defrosting system is mandatory. The sensor is the “eyes” of the system, and if they are closed or damaged, the refrigerator goes blind.
- 🧊 A thick layer of ice or a snow coat is visible on the back wall of the freezer.
- 🌡️ In the refrigerator compartment, the temperature is higher than normal, despite the operation of the compressor.
- 🔊 Extraneous noise, crackling or humming has appeared caused by the operation of the fan touching the ice.
- ⚡ Indicators are blinking on the control panel or an error code associated with defrosting is on (often F07, F10 or similar).
Sensor location and preparation for diagnostics
B refrigerators Hotpoint-Ariston No Frost The defrost sensor is usually located directly on the evaporator tubes in the freezer. To access it, you need to remove the rear plastic panel inside the freezer. In some models, access may be difficult due to the presence of ice, so preliminary complete defrosting of the unit for 24 hours is a mandatory preparation step.
To carry out the work, you will need a minimum set of tools: a Phillips screwdriver for removing the panel, pliers and, most importantly, a working one (tester). Without a measuring device, diagnosis is impossible, since it is impossible to visually determine the integrity of the thermistor - it looks like an ordinary metal or plastic “bullet” with two wires. It is also useful to have a hair dryer on hand to speed up defrosting, but you need to use it carefully so as not to melt the plastic. multimeter (tester). Without a measuring device, diagnosis is impossible, since it is impossible to visually determine the integrity of the thermistor - it looks like an ordinary metal or plastic “bullet” with two wires. It's also helpful to have a hair dryer on hand to speed up defrosting, but use it carefully to avoid melting the plastic.
After removing the back panel, you will see the aluminum evaporator heat sink. The sensor can be inserted into a special hole in the evaporator tubes (filled with heat-conducting paste) or attached to them with a clip. The wires from the sensor go to a connector that connects it to the main wiring of the refrigerator. Find this connector - it is most convenient to connect the part by disconnecting it from the main circuit.
Step-by-step instructions: how to test a sensor with a multimeter
The testing process involves measuring the electrical resistance of the sensor at a certain temperature. Since the thermistor changes its properties depending on the heating, simply ringing it for a “break” is not enough - you need to compare the readings with reference values. To begin, set the multimeter to resistance measurement mode (Ohm, limit 20 kOhm or 200 kOhm).
Connect the multimeter probes to the contacts of the sensor connector. Polarity is not important in this case, since this is a passive element. If the device screen displays a unit on the left (or an infinity symbol), this means an open circuit - the sensor is definitely faulty and requires replacement. If the device shows zero or a value close to zero, a short circuit is possible, which is also a defect.
The most accurate way to check is to compare the resistance at room temperature and during heating/cooling. At room temperature (about +20...+25°C), a working Hotpoint-Ariston sensor usually shows a resistance in the range from 4 to 7 kOhm (values may vary depending on the specific model and color marking of the wires). To check the reaction to temperature, you can hold the sensor in your hand or gently blow warm air on it - the readings on the multimeter should begin to change (fall) in real time.
☑️ Algorithm for checking the sensor
If the resistance does not change when heated or remains at the level of a break/short circuit, the part is considered inoperative. Even if the readings seem close to normal, but do not fall within the acceptable range, this can cause malfunctions in the controller's operating algorithm, which expects strictly defined values to transition between cycles.
⚠️ Attention: Do not try to test the sensor without disconnecting it from the refrigerator control board. In this case, you will measure the resistance of the entire circuit, including other parallel-connected elements, which will give an incorrect result.
Table of normal resistance values
Different models of refrigerators may be equipped with sensors with different characteristics. Below is a table with approximate resistance values for the most common types of thermistors used in Hotpoint-Ariston equipment. The exact data is often indicated on the body of the sensor itself or in the service documentation.
| Sensor type (wire color) | Temperature +25°C | Temperature 0°C | Temperature -20°C |
|---|---|---|---|
| Standard (white/black) | 5.0 kOhm | 8.5 kOhm | 25.0 kOhm |
| High temperature (green) | 4.7 kOhm | 7.8 kOhm | 22.0 kOhm |
| Low temperature (blue) | 6.2 kOhm | 10.5 kOhm | 30.0 kOhm |
| Specific (red) | 10.0 kOhm | 18.0 kOhm | 55.0 kOhm |
Please note that the values in the table are averaged. Actual resistance may vary slightly depending on your multimeter's calibration and actual room temperature. The main thing is that the value is not zero or infinity, and that it changes smoothly as the temperature changes.
What to do if you don’t have a multimeter?
If you don’t have a tester at hand, you can try the elimination method. Replace the suspect sensor with a new one that is known to be good. If the problem disappears, the old sensor was faulty. However, this method requires the purchase of a new part and does not guarantee that it was the problem, since the heating element could also burn out.
Replacement of the faulty element and assembly of the system
If the diagnostics confirmed the malfunction, the sensor must be replaced. Refrigerators Hotpoint-Ariston usually use universal defrost sensors, which are easy to find in spare parts stores. When purchasing, pay attention to the length of the wire and the type of connector - sometimes they have to be re-soldered from the old sensor, observing the color marking.
To replace, carefully cut the wires of the old sensor closer to its body to leave the maximum length for the connection. Strip the ends of the wires of the new and old sensor, twist them according to color and carefully insulate them. For insulation, it is best to use heat-shrink tubing, which is heated with a hairdryer or lighter, ensuring a tight connection, which is critical in conditions of high humidity.
Install the new sensor in the same position where the old one was. If it was inserted into a hole in the evaporator, be sure to use thermal conductive paste (KPT-8 or equivalent) to ensure fast and accurate heat transfer. Without paste, the sensor will display the temperature with a delay, which will lead to incorrect operation of the system.
After installation, reassemble the structure in the reverse order: install the back panel, fasten the screws, connect the refrigerator to the network. Check the fan operation and make sure that after a few hours of operation, excess ice does not form on the evaporator. Complete restoration of normal operation of the system can take up to 24 hours.
Frequent errors in diagnostics and prevention
One of the most common mistakes is an attempt to replace only the sensor, ignoring the condition of the others elements of the defrost system. Often, together with the sensor, Defrost heating element or the fuse fails. If you replace only the sensor, the new one may quickly burn out or the system will continue to operate incorrectly due to a faulty heater.
Another mistake is poor wire insulation. In the freezer, cycles of freezing and thawing of moisture constantly occur, and condensation forms. If the twist insulation is leaky, moisture will reach the copper, oxidation and electrocorrosion will begin, which will lead to a re-break of the circuit after several months of operation.
To prevent problems with the No Frost system, it is recommended to regularly check the tightness of the door seals. If warm, humid air enters the chamber, the load on the defrost system increases many times over, and the sensors may not be able to cope with the rapid freezing of ice. Also, you should not load food into the freezer without pre-cooling, if possible.
What error code indicates a malfunction of the sensor in Hotpoint-Ariston?
In most models of Hotpoint Ariston refrigerators, problems with the defrosting system (including the sensor, heating element or timer) are indicated by an error code F07 or The temperature indicator in the freezer compartment is flashing. However, codes may vary depending on the year of manufacture and the specific series of the refrigerator. It is better to look for the exact decoding in the instructions for your model.
Is it possible to temporarily operate a refrigerator with a faulty sensor?
You can operate a refrigerator with a faulty defrost sensor only in emergency mode and for a short time. You will have to regularly (every 3-5 days) defrost the refrigerator manually, turning it off completely for a day. If this is not done, the ice will completely block the air channels, the compressor will work without stopping and may burn out from overheating.
Where to buy an original defrost sensor?
Original spare parts for Hotpoint-Ariston are best ordered from authorized service centers or specialized spare parts stores for household appliances, indicating the exact model number (PNC) of your refrigerator. Universal analogues also work effectively if their resistance parameters match the original.
Why doesn’t the new sensor solve the ice problem?
If replacing the sensor did not help, the reason may be a malfunction of the control module that does not process signals, or a break in the wiring between the sensor and the board. It is also worth checking the defrost heating element and the fuse - they could have failed at the same time or earlier, and the symptoms appeared later.