Mitsubishi Electric MXZ-8B140VA Technical & Service Manual page 30

Abnormal point and detection method
Error Code
(1) Too low superheat due to low dis-
charge temperature
Abnormal if discharge superheat is contin-
uously detected -15: or less even though
linear expansion valve has minimum open
pulse after compressor starts operating for
10 minutes.
(2) Erroneous connection of refrigerant
U7
pipes or the connecting wires
(1520)
Consider the stopping indoor unit abnor-
mal if condenser/evaporator temperature
thermistor (TH5 or RT12) detects -5: 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: 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
• Instantaneous decrease of DC bus voltage
to 200V
• Increase of DC bus voltage to 400V
U9
• Decrease of input current of outdoor unit
(4220)
to 0.5A only if operation frequency is more
than or equal to 40Hz or compressor cur-
rent 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)
OCH480A
Case
1 Disconnection or loose
connection of compressor
temperature thermistor. (TH4)
2 Defective holder of discharge
temperature thermistor
1 Failure in piping/wiring
2 Pipe (liquid) is clogged or
crushed.
1 Failure in the operation of
the DC fan motor
2 Failure in the outdoor circuit
controller board
1 Decrease of power supply voltage
2 Disconnection of compressor
wiring
3 Defective 52C
4 Defective ACT module
5 Defective ACT module drive
circuit of outdoor power circuit
board
6 Disconnection or loose connec-
tion of CNAF
7 Defective 52C drive circuit of
outdoor controller circuit board
8 Disconnection or loose
connection of CN5 on the
outdoor power circuit board
9 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
30
Judgment and action
12 Check the installation conditions of
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.
1 Check or replace the DC fan motor.
2 Check the voltage of the outdoor circuit
controller board during operation.
3 Replace 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 8-7.
3 Replace noise filter circuit board.
4 Replace ACT module.
5 Replace outdoor power circuit board.
6 Check CNAF wiring.
7 Replace outdoor controller circuit board.
(12V DC output)
8 Check CN5 wiring on the outdoor power
circuit board.
Refer to 8-7.
9 Check CN2 wiring on the outdoor power
circuit board.
Refer to 8-7.
1 Open stop valve.
2 Check facility of power supply.
3 Correct the wiring (U·V·W phase) to
compressor.
Refer to 8-7.
4 Check compressor.
Refer to 8-6.
5 Replace outdoor power circuit board.