How to make a thermostat for the refrigerator with your own hands: step-by-step instructions with diagrams

• 🔌 Disconnect the refrigerator from the network.
• 🔌 Find the thermostat terminals (usually they are labeled L (phase), N (zero) and COM (output to the compressor)).
• 🔌 Connect the phase (L) to the terminal IN on W1209, and the output OUT to the compressor.

The W1209 module is configured to the required temperatures (T1 and T2)|

The NTC sensor is securely fixed in the refrigerator compartment|

All connections are insulated with heat shrink|

The refrigerator is disconnected from the network during installation-->

For clarity, a simplified connection diagram:

220V ~
│
├───[W1209 IN]───[W1209 OUT]───[Compressor]
│
├───[W1209 N]───[Network zero]
│
└───[NTC sensor]───(inside the refrigeration cameras)

⚠️ Attention: If your refrigerator uses inverter compressor (for example, in models Samsung Digital Inverter), the circuit with W1209 may not be suitable. For such cases, you will need PWM controller or a specialized controller.

4. Alternative circuits: Arduino and ready-made modules

If you need more flexible settings (for example, different temperatures for the refrigerator and freezer compartments), consider the circuit based on Arduino. It is more difficult to assemble, but allows:

• 📊 Data temperature log to the SD card.
• 📱 Manage the refrigerator via Wi-Fi (with ESP8266).
• ⚡ Implement emergency shutdown at critical values.

Example code for Arduino Nano (relay control by temperature):

#include 
#include 

#define ONE_WIRE_BUS 2 // Pin for DS18B20 sensor
#define RELAY_PIN 3 // Relay pin

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

float targetTemp = 4.0; // Target temperature
float hysteresis = 1.0; // Hysteresis

void setup() {
pinMode(RELAY_PIN, OUTPUT);
digitalWrite(RELAY_PIN, HIGH); // Relay off (NO contact)
sensors.begin();
}

void loop() {
sensors.requestTemperatures();
float currentTemp = sensors.getTempCByIndex(0);

if (currentTemp > targetTemp + hysteresis) {
digitalWrite(RELAY_PIN, LOW); data-i="201">digitalWrite(RELAY_PIN, HIGH); // Turn off the compressor
} else if (currentTemp < targetTemp - hysteresis) {
digitalWrite(RELAY_PIN, HIGH); // Turn off the compressor
}
delay(5000); // Delay 5 seconds
}

This circuit will require a sensor DS18B20 (more accurate than NTC) and libraries OneWire i DallasTemperature. You can download them through the library manager in Arduino IDE.

Ready solutions:

• 🔹 Module INKBIRD ITC-308 (3,000–4,000 ₽) - supports two zones (refrigerator + freezer), control via Bluetooth.
• 🔹 Controller STC-1000 (1,500–2,000 ₽) - a simple but reliable option with manual settings.

5. Calibration and testing of a homemade thermostat

After assembly, the device need calibrate and test in real conditions. To do this:

1. Checking the sensor:
   • 🌡️ Place the sensor in a glass with melting ice (0°C) and check the readings with a multimeter or through menu W1209.
   • 🔥 Then place the sensor in hot water (~50°C) and check the values again.
2. Hysteresis setting:
   • 📉 Hysteresis (difference between on/off) should be 1–2°C for the refrigerator compartment and 3–5°C for the freezer.
   • 🔧 If the compressor turns on too often, increase the hysteresis.

• ⏱️ Connect the device and observe the operation of the compressor for 6–12 hours.
• 📊 Use external thermometer (for example, Xiaomi Mijia) to check the accuracy.

Typical errors and their solutions:

6. Safety and operating recommendations

Homemade devices require special attention electrical safety and operating conditions. Follow these rules:

• ⚡ Insulation of all connections: Use heat-shrink tubing or electrical tape. This is especially true for places where wires may come into contact with the metal body of the refrigerator.
• 🔌 Grounding: If your network has a ground, connect it to the metal body of the thermostat (if it is metal).
• 🌡️ Control. humidity: The temperature sensor must be protected from condensation. Use a sealed case or silicone case.
• 🔄 Backup shutdown: Install an additional switch in the circuit for emergency shutdown of the compressor.

If you use Arduino or ESP8266, ensure stable power supply:

• 🔋 Use a power supply with 5V/1A protected from surges.
• 🔌 Do not connect the board directly to 220V - only through a step-down transformer or a USB adapter.

⚠️ Attention: In refrigerators with a No Frost system, the thermostat controls not only the compressor, but also fan and defrost heating element. A home-made device may not work correctly with these elements, which will lead to icing of the evaporator. In such cases, it is recommended to use original thermostat or a specialized controller (for example, INKBIRD ITC-308).

7. Comparison of homemade and factory thermostat

Before deciding to assemble the device yourself, evaluate the pros and cons of each option:

A homemade thermostat is justified in the following cases:

• 🔧 The refrigerator is old, and the original thermostat has not been produced for a long time.
• 💰 The budget is limited, and service repairs are too expensive.
• 🛠️ You love experiments and are ready to refine the circuit.

A factory thermostat is worth choosing if:

• 🔹 The refrigerator is under warranty (homemade modification will cancel it).
• 🔹 You have a model with No Frost or an inverter compressor.
• 🔹 You need maximum accuracy and reliability.

Frequently asked questions (FAQ)