Mitsubishi Electric MXZ-8B48NA Technical & Service Manual page 46

Abnormal point and detection method
Error Code
(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.
WCheck 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)
Symbol
U4
TH3 Thermistor <Outdoor pipe>
(TH3:5105)
Thermistor <Outdoor>
TH7
(TH7:5106)
Internal thermistor <Heatsink>
TH8
(TH8:5110)
Branch box unit
(63HS:5201)
TH-A~E Thermistor
( )
TH-A~E
(Room A-E) (Gas pipe temperature detection)
:5131
(2) High-Pressure sensor (63HS) abnormality
1When detected pressure in high-pressure
sensor is 1MPa [145PSIG] or less during
the operation, the compressor stops and
restarts operation in 3 minutes.
2When the detected pressure is 1MPa
[145PSIG] or less at just before of restart-
ing, the compressor stops abnormally. In
this time, <U4> is displayed.
3For 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.
4For 3 minutes after starting compressor,
for defrosting or for 3 minutes after recov-
ery from defrosting, abnormality is not
determined as abnormality.
Abnormal temperature of heatsink
Abnormal if heatsink thermistor (TH8)
detects temperature indicated 93 °C [200 °F]
U5
(4230)
Abnormality of power module
Check abnormality by driving power module
in case overcurrent is detected.
U6
(UF or UP error condition)
(4250)
1One 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.
2Defective thermistor
3Outdoor controller circuit board
is defective.
Thermistors
Name
– 40
– 40
– 35
– 40
1High-pressure sensor failure
2Internal pressure decrease by
gas leakage
3Connector contact failure dis-
connection
4Controller board input circuit
failure
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
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
Case
1 Check the connector's contact and the electric
wires of thermistor.
2Check the resistance value of thermistors or
the temperatures by referring to the section of
"Monitoring function for outdoor unit".
(Convert modes by SW2.)
3Replace the whole outdoor controller board.
Open detection Short detection
[– 40°F] or below 90 [194°F] or above
[– 40°F] or below 90 [194°F] or above
[– 30°F] or below 170 [338°F] or above
[– 40°F] or below 90 [194°F] or above
1 Check the high-pressure sensor.
2 Check the internal pressure.
3 Check the high-pressure sensor.
4 Check the outdoor controller board
12 Check outdoor fan.
3 Check air flow path for cooling.
4 Check if there is something which causes
5 Check resistance value of thermistor (TH8)
6 Replace outdoor power circuit board.
7 Replace outdoor controller circuit board.
1 Open stop valve.
2 Check facility of power supply.
3 Correct the wiring (U·V·W phase) to
4 Check compressor referring to 9-6.
5 Replace outdoor power circuit board.
46
Judgment and action
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.
or temperature by microprocessor.
(Thermistor/TH8: Refer to 9-6.)
(SW2 on A-Control Service Tool: Refer to 9-8.)
compressor. Refer to 9-7.