Outdoor Fan Motor; Too Low Superheat Due To Low Discharge Temperature; Overvoltage Error; Undervoltage Error - Mitsubishi Electric SUZ-KA24NAHZ Service Manual

Check Code
Abnormal point and detection method
Too low superheat due to low discharge
temperature
Abnormal if discharge superheat is con-
tinuously detected less than or equal to
5˚F [−15˚C] for 3 minutes even though
linear expansion valve has minimum open
U7
pulse after compressor starts operating for
(1502)
10 minutes.

Outdoor fan motor

Abnormal if rotational frequency of the fan
motor is not detected during DC fan motor
operation.
Fan motor rotational frequency is abnormal if;
U8
• 100 rpm or below detected continuously
(4400)
for 15 seconds at 68-F [20°C] or more
outside air temperature.
• 50 rpm or below or 1500 rpm or more
detected continuously for 1 minute.
To find out the detail history (latest) about U9 error, turn ON SW2-1, 2-2 and 2-6.
Detailed
Refer to "10-9. FUNCTION OF SWITCHES, CONNECTORS AND JUMPERS".
codes

Overvoltage error

• Increase in DC bus voltage to
430 V
01

Undervoltage error

• Instantaneous decrease in DC
bus voltage to 200 V
02
U9
(4220)
Input current sensor error
• Decrease in input current
through outdoor unit to 0.5 A
only if operation frequency is
more than or equal to 40 Hz
or compressor current is more
than or equal to 6 A.
04
OCH754A
Cause
1 Disconnection or loose connec-
tion of discharge temperature
thermistor (TH4)
2 Defective holder of discharge
temperature thermistor
3 Disconnection or loose connection
of linear expansion valve's coil
4 Disconnection or loose connec-
tion of linear expansion valve's
connector
5 Defective linear expansion valve
1 Failure in the operation of the
DC fan motor
2 Failure in the outdoor circuit
controller board
1 Abnormal increase in power
source voltage
2 Disconnection of compressor
wiring
3 Defective outdoor power circuit
board
4 Compressor has a ground fault.
1 Decrease in power source
voltage, instantaneous stop.
2 Defective converter drive circuit
in outdoor power circuit board
3 Defective 52C drive circuit in
outdoor power circuit board
4 Disconnection or loose
connection of CN2 on the
outdoor power circuit board /
controller circuit board
5 Power circuit failure on DC
supply for 15 VDC output on
outdoor controller circuit board
1 Defective input current detection
circuit in outdoor power circuit
board
2 Defective outdoor controller
circuit board
30
Judgment and action
12 Check the installation conditions of dis-
charge temperature thermistor (TH4).
3 Check the coil of linear expansion valve.
Refer to "10-6. HOW TO CHECK THE
COMPONENTS".
4 Check the connection or contact of LEV-A and
LEV-B on outdoor controller circuit board.
5 Check linear expansion valve. Refer to "10-5.
HOW TO CHECK THE PARTS".
1 Check or replace the DC fan motor.
2 Check the voltage of the outdoor circuit con-
troller 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 field facility for the power supply.
2 Correct the wiring (U . V . W phase) to
compressor. Refer to "10-8. TEST POINT
DIAGRAM" (Outdoor power circuit board).
3 Replace outdoor power circuit board.
4 Check compressor for electrical insulation.
Replace compressor.
1 Check the field facility for the power supply.
2 Replace outdoor power circuit board.
3 Replace outdoor power circuit board.
4 Check CN2 wiring.
5 Replace outdoor controller circuit board.
1 Replace outdoor power circuit board.
2 Replace outdoor controller circuit board.