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Installation and Maintenance
Service Manual
4. Malfunction of Zero-crossing Inspection Circuit Malfunction of the IDU Fan Motor U8
Main detection points:
● Instant energization afte de-energization while the capacitordischarges slowly?
● The zero-cross detectioncircuit of the mainboard is dened abnormal?
Malfunction diagnosis process:
Turn power off for 
1minute,the turn 
back on
The unit returns to normal. 
Conclusion:U8 is displayed due to 
power off/on while the
capacitor discharges slowly.
U8 is still 
displayed
The zero-cross detection circuit 
of the mainboard is dened 
abnormal.Replace the mainboard 
with the same model
Yes
No
Start
End