**English Translation:**
The Haier inverter air conditioner does not cool, and the outdoor unit does not operate.
**Fault Phenomenon:** The air conditioner does not cool, and the outdoor unit does not operate.
**Source of Information:** Beijing Haier Air Conditioning After-sales Service Phone - [http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3489688](http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3489688).
**Maintenance Process:**
Upon on-site inspection, when the remote control was used to turn on the air conditioner, the main relay on the indoor unit motherboard engaged, supplying power to the outdoor unit. However, the outdoor unit did not operate. 2mm later, the main relay on the indoor unit motherboard disconnected. For the Haier air conditioner, after pressing the "sensor" toggle key twice on the remote control, the indicator light displayed a fault code, which indicated a communication failure. After 3 minutes, the indoor unit motherboard again supplied power to the outdoor unit. Using a multimeter set to the DC voltage range, the voltage between the N terminal and the communication S terminal of the outdoor unit was measured as 0V. This voltage is provided by the indoor unit motherboard, and under normal conditions, it should be a fluctuating DC voltage within 24V. At the wiring terminals of the indoor unit, the outdoor unit connection wires were removed, and the voltage was still measured as 0V, indicating that the fault lies in the indoor unit motherboard. After removing the indoor unit housing, the voltage across the stabilizing diode was measured as 0V. Analyzing the communication voltage generation circuit, the L terminal passes through resistor Rl0 for voltage reduction, D6 for rectification, C6 for filtering, and ZD1 for stabilization, forming a stable DC 24V voltage with the N terminal. This part of the circuit is relatively simple. Using the AC voltage range of the multimeter, the voltage before the rectifier diode was measured as 0V. After disconnecting the power, the resistance value of resistor R10 was measured with the ohmmeter range of the multimeter, showing an infinite value, indicating that it has already opened. After replacement, during testing, the voltage between the N terminal and the S terminal at the wiring terminals of the indoor unit was measured as DC 24V. After reconnecting the outdoor unit connection wires and testing, the outdoor unit started, cooling functioned normally, and the fault was resolved.