Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 311

[ IX Troubleshooting ]
4. Troubleshooting according to the remote controller malfunction or the external input error
(1) In the case of MA remote controller
Phenomena
1 Even if the operation button on
the remote controller is
pressed, the display remains
unlit and the unit does not start
running.(Power indicator
does not appear on the
screen.)
Cause
1. The power is not supplied to the
indoor unit.
(i) The main power of the indoor
unit is not on.
(ii) The connector on the indoor
unit board has come off.
(iii) The fuse on the indoor unit
board has melted.
(iv) Transformer failure and dis-
connected wire of the indoor
unit.
2. Incorrect wiring for the MA remote
controller
(i) Disconnected wire for the MA
remote controller or disconnect-
ed line to the terminal block.
(ii) Short-circuited MA remote con-
troller wiring
(iii) Incorrect wiring for the MA re-
mote controller to the terminal
block for transmission line con-
nection (TB5) on the indoor unit
(iv) Reversed connection of the
wire for the MA remote control-
ler and the AC208 / 230V power
wire
(v) Reversed connection of the
wire for the MA remote control-
ler and the M-NET transmission
line on the indoor unit
3. The number of the MA remote
controllers that are connected to
an indoor unit exceeds the allow-
able range (2 units).
4. The length or the diameter of the
wire for the MA remote controller
are out of specification.
5. Short circuit of the wire for the re-
mote display output of the outdoor
unit or reversed polarity connec-
tion of the relay.
6. The indoor unit board failure
7. MA remote controller failure
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Check method and remedy
(1) Measure voltages of the MA remote
controller terminal (among (i) to (iii)).
If the voltage is between DC 8.5 and
12V, the remote controller is a failure.
If no voltage is applied
Check (1) described on the left. If the
cause is found, correct it.
If no cause is found, refer to 2).
(2) Remove the wire for the remote control-
ler from the terminal block (TB13) on
the MA remote controller for the indoor
unit, and check voltage among (i) to (iii).
If the voltage is between DC 8.5 and
12V
Check the (2). (iv) described on the
left.
If no voltage is applied
Check 1. described on the left. If the
cause is found, correct it.
If no cause is found, check the wire for
the remote display output (the relay
polarity).
If no further cause is found, replace the
indoor unit board.