LG ARUN Series Service Manual page 117

Error No. Error Type
74*
Master 741 3 Phase Power Unbalance
Slave 742
I Error Diagnosis and Countermeasure Flow Chart
Is inverter PCB assembly
power wiring normal?
Yes
Is input voltage normal?
Yes
Does indoor unit power
bridge R,S,T phase equally?
Yes
Is inverter PCB
assembly normal?
Yes
Recheck power and
installing condition
Measuring input voltage
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Error Point
During operation(compressor fre-
quency is over 50Hz), difference
between R & T phase is 5A for 10
seconds.
No
Check abnormal wiring between Inverter PCB assembly & bridge diode
(misconnection,disconnection)
¡ Rewiring if abnormal wiring found
Check
No
R~S/S~T/T~R Phase voltage : 460V±10% (3Ø 460V)
¡ Check connection condition and wiring if power is abnormal
No
Bridge R-N,S-N,T-N voltage equally (3Ø 460V)
No
Replace inverter PCB assembly
Inverter PCB & Bridge Diode wiring
Checking joining condition
- 117 -
Troubleshooting Guide
Main Reasons
1. CT sensor defect
2. Capacity over of AVR
208/230V±10% (3Ø 208/230V)
LGE Internal Use Only