Mitsubishi Electric MUH-GA35VB Service Manual page 26

When OPERATION INDICATOR lamp flashes 0.5-second intervals or 1-time.
Outdoor unit does not operate.
D D How to check mis-wiring and serial signal error
Make them sure.
1. Turn OFF the power supply
2. Short-circuit between indoor terminal block N and 3.
3. Turn ON the power supply
Is there 5V DC between J205 + –J101 - on the deicer P.C. board?
As for indoor unit MSC type, refer to service manual OB385 or OB393.
Start
Turn OFF the power supply(indoor/outdoor unit).
Is the outdoor unit "MUH" type?
•Turn ON the power supply(indoor/outdoor unit).
•Press once EMERGENCY OPERATION switch.
•3 min. later, check the self-check result
displayed on OPERATION INDICATOR
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lamp on indoor unit. 2
Serial signal error is indicated.
(0.5-sec. ON, 0.5-sec. OFF)
Yes
Is this mis-wiring, poor contact,
or disconnection of wire?
No
and disconnect indoor and outdoor connecting wire on indoor side.
(indoor/outdoor unit)
and press once EMERGENCY OPERATION switch.
(indoor unit)
Is there 20V DC between both ends of
R132 on indoor electronic control P.C.
board ?
( By tester, the stylus is between 0 ~ 20V. )
•Turn OFF the power supply(indoor unit).
•Connect ON indoor and outdoor connecting wire.
Turn ON the power supply(outdoor unit).
Is there 230V AC between outdoor terminal
block L-N (TB1)?
Turn ON the power supply(indoor unit).
During EMERGENCY OPERATION,
is there 10V DC between both ends
of R601?
(By tester, the stylus is between 5 ~10V)
Replace the deicer P.C. board.
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1 Set the switch(SW2-2) on indoor electronic control P.C. board to
MU or MUX type, when the outdoor unit is MU or MUX type.
If the setting is MUH or MXZ type, the unit does not work.
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2 Short circuit of JPG and JPS on the indoor electronic control
P.C. board enables self-check to be displayed in 3 seconds.
No
Yes
No
Replace the indoor electronic
control P.C. board.
Yes
Check the outdoor power supply,
No
power supply cord and
connection.
Yes
Yes
Make the wiring between CN730
No
on the deicer P.C. board and
outdoor terminal block correct.
Yes
26
Set the switch(SW2-2) on the indoor electronic
control P.C. board to MU or MUX type.
Does the unit operate?
Refer to the
"Instruction of
troubleshooting."
No
Replace the deicer P.C. board.
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1
Yes
OK
No