Service manual
SiUS28-902_a Troubleshooting by Indication on the Unified ON/OFF Controller
Troubleshooting 158
Check for Fan Motor Connector
(1) Turn the power supply off.
(2) With the fan motor connector disconnected, measure the resistance between each pin, then
make sure that the resistance is more than the value mentioned in the following table.
Check for Power Transistor
Judgment is made through cable check with an analog tester.
(1) Do not touch the energized part (high voltage part) for at least 10 minutes after the power is
turned OFF.
(2) Be sure to touch the ground terminal with a hand to release static electricity from the body
(to prevent the PC board from being damaged).
(3) Also with a tester, take measurements at the following spots and confirm that residual
electric charge of the power transistor is DC 50V or less.
(4) After checking the residual electric charge, remove the connector of the outdoor unit fan
motor. When the outdoor unit fan is rotated by strong headwind, remove the connector of
the outdoor unit fan motor after confirming that the outdoor unit fan has stopped because
electrical energy is stored in the capacitor and there may be a risk of electric shock.
(5) Remove the wire connecting the power transistor and the compressor. Remove it from the
compressor terminal side. During this work, be careful not to deform the Faston terminal at
the end of the connecting wire.
(6) Using an analog tester, measure resistance and fill in the blanks in the following table.
In case of unbalanced resistance for one of the three phases in each table (when the
resistance value is equal to five times or more than the other resistance values), the power
transistor is broken.
In normal cases, each phase shows a similar resistance value.
CHECK 3
Measurement point Judgement
1 - 4 1MΩ or more
2 - 4 100kΩ or more
3 - 4 100Ω or more
4 - 7 100kΩ or more
1 White
2 Orange
3 Brown
4 Blue
5
6
7 Red
GND
CHECK 4
Tester Resistance Tester Resistance
(+) (-) Ω (+) (-) Ω
C+ U C- U ∞
C+ V C- V ∞
C+ W C- W ∞
UC+ ∞ UC-
VC+ ∞ VC-
WC+ ∞ WC-
Electrical
equipment box
Outdoor unit
fan connector
Front face Ground terminal
Residual voltage
measurement spot
U
Red
White
Blue
VW
UVW
Comp.
M1C
Outdoor Unit
PC board
C+ C-