Mitsubishi Electric MXZ-8B48NA, Technical & Service Manual, Page: 46 / 88

46
Thermistors
Open detection Short detection
Symbol Name
TH3
TH7
TH8
Branch box unit
TH-A~E
(Room A-E)
– 40 [– 40°F] or below
– 40 [– 40°F] or below
– 35 [– 30°F] or below
90 [194°F] or above
90 [194°F] or above
170 [338°F] or above
– 40 [– 40°F] or below 90 [194°F] or above
Thermistor <Outdoor pipe>
Thermistor
(Gas pipe temperature detection)
Thermistor <Outdoor>
Internal thermistor <Heatsink>
Error Code
Abnormal point and detection method
Case
Judgment and action
U4
(TH3:5105)
(TH7:5106)
(TH8:5110)
(63HS:5201)
TH-A~E
:5131
(1) Open/short circuit in the outdoor unit
thermistors (TH3, TH7, and TH8) and
branch box’s thermistors(TH-A~E)
Abnormal if open or short circuit is detected
while the compressor is operating.
Open detection of thermistors TH3 is inopera-
tive for 10 seconds to 10 minutes after com-
pressor starting and 10 minutes after recov-
ery from defrosting and during defrosting.
W
Check which unit has abnormality in its
thermistor by switching the mode of SW2.
(Refer to 9-8.)
Open/short circuit in the branch box ther-
mistor. (TH-A–TH-E)
1
One or more connectors on
outdoor controller circuit board
(TH3, TH7 and TH8) and branch
box controller board (TH-A~E)
have contact failure or discon-
nection.
2
Defective thermistor
3
Outdoor controller circuit board
is defective.
1
Check the connector’s contact and the electric
wires of thermistor.
2
Check the resistance value of thermistors or
the temperatures by referring to the section of
“Monitoring function for outdoor unit”.
(Convert modes by SW2.)
3
Replace the whole outdoor controller board.
U5
(4230)
Abnormal temperature of heatsink
Abnormal if heatsink thermistor (TH8)
detects temperature indicated 93 °C [200 °F]
1
The outdoor fan motor is locked.
2
Failure of outdoor fan motor
3
Air flow path is clogged.
4
Rise of ambient temperature
5
Defective thermistor
6
Defective input circuit of
outdoor power circuit board
7
Failure of outdoor fan drive
circuit
12
Check outdoor fan.
3
Check air flow path for cooling.
4
Check if there is something which causes
temperature rise around outdoor unit.
(Upper limit of ambient temperature is 46
:
[115°F].)
Turn off power, and on again to check if U5
is displayed within 30 minutes.
If U4 is displayed instead of U5, follow the
action to be taken for U4.
5
Check resistance value of thermistor (TH8)
or temperature by microprocessor.
(Thermistor/TH8: Refer to 9-6.)
(SW2 on A-Control Service Tool: Refer to 9-8.)
6
Replace outdoor power circuit board.
7
Replace outdoor controller circuit board.
U6
(4250)
Abnormality of power module
Check abnormality by driving power module
in case overcurrent is detected.
(UF or UP error condition)
1
Outdoor stop valve is closed.
2
Decrease of power supply voltage
3
Looseness, disconnection or
converse of compressor wiring
connection
4
Defective compressor
5
Defective outdoor power circuit
board
1
Open stop valve.
2
Check facility of power supply.
3
Correct the wiring (U·V·W phase) to
compressor. Refer to 9-7.
4
Check compressor referring to 9-6.
5
Replace outdoor power circuit board.
( )
(2) High-Pressure sensor (63HS) abnormality
1
When detected pressure in high-pressure
sensor is 1MPa [145PSIG] or less during
the operation, the compressor stops and
restarts operation in 3 minutes.
2
When the detected pressure is 1MPa
[145PSIG] or less at just before of restart-
ing, the compressor stops abnormally. In
this time, <U4> is displayed.
3
For 3 minutes after the compressor stops,
the unit delays abnormal stop. Then, the
outdoor unit address No. and check delay
code <U4> blinks alternately on the 7
SEG digital display.
4
For 3 minutes after starting compressor,
for defrosting or for 3 minutes after recov-
ery from defrosting, abnormality is not
determined as abnormality.
1
Check the high-pressure sensor.
2
Check the internal pressure.
3
Check the high-pressure sensor.
4
Check the outdoor controller board
1
High-pressure sensor failure
2
Internal pressure decrease by
gas leakage
3
Connector contact failure dis-
connection
4
Controller board input circuit
failure