Mitsubishi Heavy Industries SRK20ZG-S Tech Manual page 50

(b) Outdoor unit
Operation
Sensor
mode
Cooling
Heat exchanger
sensor
Heating
Cooling
Outdoor air
temperature sensor
Heating
Discharge pipe
All modes
sensor
(9) Checking the indoor electrical equipment
(a) Indoor unit circuit board check procedure
Is there voltage between terminal
blocks 1 and 2 ? (AC 220/230/240
V)
YES
Is the fuse burnt out? (3.15 A)
YES
Is the voltage between terminal
blocks 2 and 3 oscillating between
DC 0 and 12V?
YES
Indoor electrical components
are normal.
(b) Indoor unit fan motor check procedure
This is a diagnostic procedure for determining if the indoor unit's fan motor or the circuit board is broken down.
1) Indoor unit printed circuit board output check
a) Turn off the power.
b) Remove the front panel, then disconnect the fan motor lead wire connector.
c) Turn on the power. If the unit operates when the ON/OFF button is pressed, if trouble is detected after the voltages in
the following figure are output for approximately 30 seconds, it means that the circuit board is normal and the fan
motor is broken down.
If the voltages in the following figure are not output at connector pins No. 1, 4 and 5, the indoor unit's circuit
board has failed and the fan motor is normal.
DC several V
(4~6 V)
CNU
2) DC Fan motor resistance check
Measuring Point
1 – 3 (Red – Black)
4 – 3 (White – Black)
Shortcircuit
System can be operated normally.
Defrosting is not performed.
System can be operated normally.
Defrosting is not operated.
Compressor overload protection is disabled.
(Can be operated.)
NO
Inspect power source
for outdoor unit.
NO
Replace fuse.
NO
Replace printed
circuit board.
(–)
GND
DC15V
6 5 4 3
6 5 4 3
FM
I
Resistance when Normal
25 MΩ or higher
30 kΩ or higher
Phenomenon
System can be operated normally.
Defrosting is performed for 10 minutes at approx. 45 minutes.
System can be operated normally.
Defrosting is performed for 10 minutes at approx. 45 minutes.
Compressor stop
DC 308~336V
Indoor unit
circuit board
2 1
2 1
Notes (1) Remove the fan motor and measure it without power connected to it.
Notes (2) If the measured value is below the value when the motor is normal, it means
that the fan motor is faulty.
47
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Broken wire