Mitsubishi Electric MSZ-HM09NA-U1 Service Manual page 18

2. Indoor unit failure mode table
Upper lamp of OP-
Abnormal point
ERATION INDICA-
(Failure mode)
TOR lamp
Not lighted Normal
1-time ash every Room temperature
0.5-second thermistor
Indoor coil
2-time ash
2.5-second OFF
thermistor
3-time ash
Serial signal
2.5-second OFF
11-time ash
Indoor fan motor
2.5-second OFF
12-time ash Indoor control
2.5-second OFF system
NOTE: Blinking patterns of this mode differ from the ones of TROUBLESHOOTING CHECK TABLE (9-4.).
OBH746B
Condition
—
The room temperature thermistor short or
open circuit is detected every 8 seconds dur-
ing operation.
The indoor coil thermistor short or open circuit
is detected every 8 seconds during operation.
The serial signal from outdoor unit is not re-
ceived for a maximum of 6 minutes.
The rotational frequency feedback signal is
not emitted for 12 seconds after the indoor fan
motor is operated.
It cannot properly read data in the nonvolatile
memory of the indoor electronic control P.C.
board.
18
Remedy
—
Refer to the characteristics of the room temperature
thermistor (9-7.).
Refer to the characteristics of the main indoor coil ther-
mistor, the sub indoor coil thermistor (9-7.).
Refer to 9-6. "How to check miswiring and serial
signal error".
Refer to 9-6. "Check of indoor fan motor".
Replace the indoor electronic control P.C. board.