Mitsubishi Electric PUHY-HP72 Service Handbook page 184

[7-8 Error Code Definitions and Solutions: Codes [6000 - 6999] ]
7-8-22 Error Code [6842]
1. Error code definition
A control communication transmission/reception hardware trouble
2. Error definition and error detection method
Indoor/outdoor unit communication error (Transmitting error)
Abnormal if "1" receiving is detected 30 times continuously though indoor controller board has transmitted "0".
3. Cause, check method and remedy
(1) Defective transmitting receiving circuit of indoor controller board
(2) Noise has entered into power supply.
(3) Noise has entered into outdoor control wire.
Note: Refer also to the Service Handbook for the indoor units.
HWE18240_GB
Cause Check method and remedy
Turn the power off, and on again to check. If
abnormality generates again, replace indoor
controller board.
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