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6.1.16 C21 - Abnormal communication between IDU and ODU
Error display
Faulty IDU: The fan continues running, and the EXV is closed. Other IDUs of the same system: The fan
continues running, the EXV is closed, and error code "A51" is displayed (V6 platform IDU displays the code
"Ed"). Meaning of the code: ODU fault
Error impact
ODU of the same system:
Error trigger
If the IDU has not received any communication signal from ODU for 3 min
Error recovery
Automatic recovery
Possible cause
See the Troubleshooting section.
Troubleshooting
Note 1: If you measure the resistance between ports P, Q, and E of the IDU main control board, normally
the resistance between P and Q is 120 Ω, the resistance between P and E is infinite, and the resistance
between Q and E is infinite.
Digital display
stops.
Error code "C26" is displayed (V6 platform ODU displays the code "H7"). Meaning of the code: IDU qty
decrease fault
If the indoor and outdoor units communicate via RS-485(PQE/PQ):
C21 (6)
If th e in door and outdoo r un its
commu nicate via RS-485
(PQE/PQ)
Panel, display box, and wired controller
Cause 1: P/Q/E co mmun ica tion
cable short-circuits or cuts off (1)
Cause 2: Commu nicatio n cabl es
are not co nnecte d in a series
Cause 3: Cable P or Q is
connected to por t E
Cause 4: The co mmuni cation
cable does not ha ve a shield
layer
Cause 5: Inte rfer ed by
stro ng-current power ca bles
(over 220 V)
Cause 6: Inte rfer ed by
electromagne tic r adiation source
(transfo rme r/high-power
fluorescent la mp, etc.)
Cause 7: Differen t
commu nicatio n n etworks (M1M2,
PQE, X1X2) are conne cted
Cause 8: The IDU main control
boa rd o r O DU ma in con trol boa rd
is d ama ged
V8 VRF Indoor Units
Display position
Pro perly conn ect the
cable
Conne ct the cables i n a
series
Conne ct P/Q/E to the
righ t port
Use shield ed cab les
Sep arate the
commu nicatio n cable
from the stron g-current
power cable
Elimina te sources of
interference or add one
more shield to the ca ble
Conne ct the
commu nicatio n cable to
the right p ort based on
the type of the
commu nicatio n n etwork
Replace th e d amaged
main co ntr ol b oard
61
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