Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 312

Phenomena
2 When the remote controller op-
eration SW is turned on, the
operation status briefly ap-
pears on the display, then it
goes off, and the display lights
out immediately, and the unit
stops.
Check method and remedy
Same symptom for all units in a
system with one outdoor unit?
YES
Check the
self-diagnosis LED
Is the error code 7120
displayed?
NO
Check 1).
Refer to [4] .6. (2) "Outdoor unit transmission power source circuit
failure judgment" for the check method.
Cause
1. The power for the M-NET trans-
mission line is not supplied from
the outdoor unit.
2. Short circuit of the transmission
line.
3. Incorrect wiring of the M-NET
transmission line on the outdoor
unit.
Disconnected wire for the MA re-
mote controller or disconnected
line to the terminal block.
The indoor transmission line is
connected incorrectly to the
transmission terminal block for
centralized controller (TB7).
The male power supply connec-
tors on the multiple outdoor units
are connected to the female
power supply switch connector
(CN40).
In the system to which the power
supply unit for transmission lines
is connected, the male power
supply connector is connected to
the female power supply switch
connector (CN40) on the out-
door unit.
4. Disconnected M-NET transmis-
sion line on the indoor unit side.
5. Disconnected wire between the
terminal block for M-NET line
(TB5) of the indoor unit and the in-
door unit board (CN2M) or discon-
nected connector.
NO
YES
Check for
2 and 3.
Correct the error.
- 303 -
[ IX Troubleshooting ]
Check method and remedy
When 2. and 3. apply, check code 7102
will be displayed on the self-diagnosis
LED.
Measure voltages of the
terminal block for transmission
line (TB5) on the indoor unit.
NO
17 - 30V?
Check 4.
YES
Check 5.
YES
Error found?
Correct
the error.
NO
Indoor unit board or
MA remote controller failure