Daikin VRV EMERION REYQ-AATJA Service Manual page 428

Troubleshooting by Error Code
421
A
Are the
indoor-outdoor
NO
and outdoor-outdoor
transmission wirings
normal?
YES
Disconnect
the outdoor-outdoor
NO
transmission wiring.
Does the system normally
operate with a single
transmission
line?
YES
U4-03
Indication after
YES
launch test
operation?
NO
Operate all indoor units.
NO
Do all units display U9?
YES
NO
Did 2 minutes or more
elapse after U9 is
displayed?
YES
SiUS372201EB
Modify the transmission
wirings.
Replace the outdoor unit main
PCB (A1P).
Mount the DIII-NET extension
adaptor.
Check controller indoor units :
(1) Some error about
thermistor, or fan motor
(M1F, M2F), electronic
expansion valve, or
defective PCB.
(2) Test operation was
interrupted by the MODE
(BS1) button.
Check all indoor error
indication.
Carry out the diagnosis again
after a lapse of 2 minutes or
more.
The PCB of indoor units
displaying U9 are normal.
Check for indoor units of
other systems to troubleshoot
them according to relevant
error codes.
Part 6 Service Diagnosis