6.1.26 C77, C78 - Abnormal communication between IDU main control board and 1# function expansion
board, abnormal communication between IDU main control board and 2# function expansion board
Panel, display box, and wired controller
Faulty IDU: The fan continues running, and the EXV is closed. Other IDUs of the same system:
operate normally.
ODU of the same system: operate normally.
If the main control board of an IDU has lost communication with 1# function expansion board or 2#
function expansion board for 2 min
See the Troubleshooting section.
C77/C78
Cause 3: The IDU main control
board is damaged
Cause 4: The function expansion
board is damaged
Cause 2: The communication
cable between the function
expansion board and the adapter
board has become loose or is
connected to a wrong port
Properly connect the
cables and ensure they
are connected to the right
ports
Replace the main control
board of the IDU
Replace the function
expansion board
Cause 1: The communication
cable between the function
expansion board and the
adapter board becomes
disconnected or short circuited
Replace the
communication cable and
properly connect the
cable
Note: The main control board of the IDU cannot be directly connected to the function expansion
board. Instead, an adapter board has to be used. See Figure 1 below:
Figure 1 Wiring diagram of function expansion board, adapter board, and IDU main control board
Function expansion
board
Adapter board
IDU main control
board
Ten-core
communication
cable
(configured by
factory)
Two-core
communication cable
(configured on site)
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