Mitsubishi Electric City Multi PQHY-P72 Service Handbook page 286

(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
Microcomputer Disconnect the control board connector and
driver circuit fail- connect the check LED as shown in the figure
ure 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.
LEV mechanism If the LEV is locked, the drive motor runs idle, and
is locked makes a small clicking sound.
When the valve makes a closing and opening
sound, the valve has a problem.
Disconnected or Measure resistance between the coils (red -
short-circuited white, red -orange, brown - yellow, brown - blue)
LEV motor coil using a tester. They are normal if resistance is
150
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%.
Incomple sealing When checking the refrigerant leak from the In-
(leak from the door unit LEV, run the target indoor unit in the fan
valve) 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.
Faulty wire con- 1. Check for loose pins on the connector and
nections in the check the colors of the lead wires visually
connector or 2. Disconnect the control board's connector and
faulty contact. conduct a continuity check using a tester.
Judgment method
6
5
4
3
2
1
LED
1 k
10%.
Thermistor
(liquid piping
temperature detection)
Linear Expansion Valve
- 277 -
[ IX Troubleshooting ]
Remedy
When the drive circuit has a prob-
lem, replace the control board.
Replace the LEV.
Replace the LEV coils.
Replace the LEV coils.
If there is a large amount of leak-
age, replace the LEV.
Check the continuity at the points
where an error occurs.
Target LEV
Indoor unit
Heat source
unit
Indoor unit
Heat source
unit
Indoor unit
Heat source
unit
Indoor unit
Indoor unit
Heat source
unit