Mitsubishi Electric City Multi CMB-P1016NU-G, Service Handbook

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[
IX
Troubleshooting ]
(3) Judgment methods and possible failure mode
Note:
The specifications of the heat source unit (heat source unit LEV) and the indoor unit (Indoor unit LEV) differ.Therefore,
remedies for each failure may vary. Check the remedy specified for the appropriate LEV as indicated in the right col-
umn.
Malfunction
mode
Judgment method Remedy Target LEV
Microcomputer
driver circuit fail-
ure Disconnect the control board connector and
connect the check LED as shown in the figure
below.
When the main power is turned on, the Indoor
unit board or the heat source unit MAIN board
outputs pulse signals to the Indoor unit LEV for
10 seconds, and to the heat source unit LEV
for 17 seconds.
If the self-diagnosis LED is not lit, or remains
lit, the driver circuit has a problem.
When the drive circuit has a prob-
lem, replace the control board. Indoor unit
Heat source
unit
LEV mechanism
is locked If the LEV is locked, the drive motor runs idle, and
makes a small clicking sound.
When the valve makes a closing and opening
sound, the valve has a problem. Replace the LEV. Indoor unit
Heat source
unit
Disconnected or
short-circuited
LEV motor coil Measure resistance between the coils (red -
white, red -orange, brown - yellow, brown - blue)
using a tester. They are normal if resistance is
150
10%.
Replace the LEV coils. Indoor unit
Measure resistance between the coils (red -
white, red -orange, brown - yellow, brown - blue)
using a tester. They are normal if resistance is 46
within 3%. Replace the LEV coils. Heat source
unit
Incomple sealing
(leak from the
valve) When checking the refrigerant leak from the In-
door unit LEV, run the target indoor unit in the fan
mode, and the other indoor units in the cooling
mode. Then, check the liquid temperature (TH22)
with the self-diagnosis LED. When the unit is run-
ning in the fan mode, the LEV is fully closed, and
the temperature detected by the thermistor is not
low. If there is a leak, however, the temperature
will be low. If the temperature is extremely low
compared with the inlet temperature displayed on
the remote controller, the LEV is not properly
sealed, however, if there is a little leak, it is not
necessary to replace the LEV when there are no
effects to other parts. If there is a large amount of leak-
age, replace the LEV. Indoor unit
Faulty wire con-
nections in the
connector or
faulty contact. 1.Check for loose pins on the connector and
check the colors of the lead wires visually
2.Disconnect the control board's connector and
conduct a continuity check using a tester.
Check the continuity at the points
where an error occurs. Indoor unit
Heat source
unit
6
5
4
3
2
1
1 k LED
Thermistor
(liquid piping
temperature detection)
Linear Expansion Valve