Mitsubishi Electric PQHY-P72ZLMU-A Service Handbook page 301

[ IX Troubleshooting ]
1. Error Code
6841
A control communication synchronism not recover
2. Error definition and error detection method
Indoor/heat source unit communication error (Transmitting error) (Heat source unit)
Abnormal if "0" receiving is detected 30 times continuously though heat source controller circuit board has transmitted "1".
Abnormal if heat source controller circuit board could not find blank of transmission path for 3 minutes.
3. Cause, check method and remedy
(1) Indoor/heat source unit connecting wire has contact failure.
(2) Defective communication circuit of heat source controller circuit
board.
(3) Noise has entered power supply.
(4) Noise has entered indoor/heat source unit connecting wire.
1. Error Code
6842
A control communication transmission/reception hardware trouble
2. Error definition and error detection method
Indoor/heat source 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 heat source control wire.
HWE15150
Cause
Cause
- 292 -
Check method and remedy
Check disconnection or looseness of indoor/
heat source unit connecting wire.
Turn the power off, and on again to check.
Replace heat source controller circuit board
if abnormality is displayed again.
Check method and remedy
Turn the power off, and on again to check. If
abnormality generates again, replace indoor
controller board.
GB