Mitsubishi Electric MXZ-8B48NA Technical & Service Manual page 47

Abnormal point and detection method
Error Code
(1) Too low superheat due to low dis-
charge/compressor temperature
Abnormal if discharge superheat is con-
tinuously detected –15: [-27°F] or less
even though linear expansion valve has
minimum open pulse after compressor
starts operating for 10 minutes.
U7
(1520)
(2) Erroneous connection of refrigerant
pipes or the connecting wires
Consider the stopping indoor unit abnormal
if condenser/evaporator temperature ther-
mistor (TH5 or RT12) detects –5: [23°F]
or below continuously for 5 minutes during
a compressor's operation in cooling mode.
Outdoor fan motor
The outdoor fan motor is considered to be
abnormal if the rotational frequency of fan
motor is abnormal when detected during
operation.
Fan motor rotational frequency is abnormal
U8
if;
(4400)
• 100 rpm or below detected continuously
for 15 seconds at 26: [79°F] or more
outside air temperature
• 50 rpm or below or 1500 rpm or more
detected continuously for 1 minute.
Overvoltage or voltage shortage and
abnormal synchronous signal to main
circuit
Abnormal if any of followings are detected
during compressor operation;
• Decrease of DC bus voltage to 310V
U9
• Instantaneous decrease of DC bus voltage
(4220)
to 200V
• Increase of DC bus voltage to 400V
• Decrease of input current of outdoor unit
to 0.5A only if operation frequency is more
than or equal to 40Hz or compressor
current is more than or equal to 5A.
Compressor overcurrent interruption
(When compressor locked)
Abnormal if overcurrent of DC bus or
compressor is detected within 30 seconds
after compressor starts operating.
UF
(4100)
Current sensor error
Abnormal if current sensor detects –1.5A
to 1.5A during compressor operation. (This
error is ignored in case of test run mode.)
UH
(5300)
Abnormal if input current exceeds 38 A or
34A continuously 10 seconds. (Current sen-
sor on noise filter board detects input current)
Case
1 Disconnection or loose
connection of discharge/com-
pressor temperature thermistor.
(TH4)
2 Defective holder of discharge/
compressor temperature ther-
mistor
1 Failure in piping/wiring
2 Pipe (liquid) is clogged or
crushed.
1Failure in the operation of
the DC fan motor
2Failure in the outdoor circuit
controller board
1 Decrease of power supply voltage
2 Disconnection of compressor
wiring
3 Defective 52C
4 Disconnection or loose connec-
tion of CNAF
5 Defective 52C drive circuit of
outdoor controller circuit board
6 Disconnection or loose
connection of CN2 on the
outdoor power circuit board
1 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 board
1 Disconnection of compressor
wiring
2 Defective circuit of current
sensor on outdoor power
circuit board
1Decrease of power supply volt-
age
47
Judgment and action
12 Check the installation conditions of dis-
charge/compressor temperature thermistor
(TH4).
1 Check piping / wiring between branch box
and indoor unit.
Refer to "Test run (Using remote controller)".
2 Check the pipe for refrigerant and change the
wrong parts.
1Check or replace the DC fan motor.
2Check the voltage of the outdoor circuit
controller board during operation.
3Replace the outdoor circuit controller
board. (when the failure is still indicated
even after performing the remedy 1
above.)
1 Check the facility of power supply.
2 Correct the wiring (U·V·W phase) to com-
pressor. Refer to 9-7.
3 Replace power circuit board.
4 Check CNAF wiring.
5 Replace outdoor controller circuit board.
(12V DC output)
6 Check CN2 wiring on the outdoor power
circuit board.
Refer to 9-7.
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.
Refer to 9-6.
5 Replace outdoor power circuit board.
1 Correct the wiring (U·V·W phase) to com-
pressor. Refer to 9-7.
2 Replace outdoor power circuit board.
1Check the facility of power supply.