A:  1. First of all, measure whether the voltage at the upper and lower ends of the circuit breaker and contactor is normal, and confirm whether there is a lack of phase, under voltage, or power loss phenomenon in the control power supply;
2. If the control electricity is normal, further check the control circuit, whether the terminals on the system IO board are loose, tighten the screws to ensure good contact;
3. Use a clamp meter to measure the running current of the fan. If the current is greater than the fan's rated current, it may be that the fan's phase sequence has changed, causing overload due to reverse operation. Replace the phase sequence.