Mitsubishi Electric MXZ-SM72TAM-U1 Service Manual page 35

0403 (Ed): Serial communication error / Model selection SW error
Abnormal points and detection methods
Serial communication between the outdoor multi controller
circuit board and outdoor power circuit board is defective.
Diagnosis of failure
Check the connection of the communication line
(CN2 and CN4) between the outdoor multi
controller circuit board and power circuit board.
Are they connected normally?
Check the wiring.
Is it connected normally?
Is the model setting correct?
OCH800A_35
No
Yes
No
Yes
No
Yes
Causes and checkpoints
• Wire breakage or contact failure of connector CN2 or
CN4
• Malfunction of power board communication circuit on
outdoor multi controller circuit board
• Malfunction of communication circuit on outdoor power
circuit board
• Incorrect setting of model selection
Connect the CN2 and CN4 properly.
Replace them in the case of breakage.
Connect the wiring properly.
Replace them in the case of breakage.
Correct the model settings.
The communication circuit of either the outdoor
controller board or power board is defective.
If unable to identify the defective circuit;
• Replace the outdoor multi controller circuit
board if it does not recover.
• Replace the outdoor power circuit board.