Hitachi RAC-25YH4, Service Manual, Page: 98 / 121

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1. Power does not come on (no operation)
Is AC230V being generated between
terminals A and B on the indoor unit
terminal board? Is AC230V being generated at AC
outlet?
Check AC outlet and breaker, and
repair any defective part.
Check the outdoor unit power circuit,
and repair any defective part.
Check according to the proper method
for checking the power circuit.
Check the reset circuit, and repair
any defective section.
Replace the microcomputer and
oscillator.
Is the control voltage being
generated normally?
12V line: 12V or 7V
5V line: 5V
Do the air deflectors perform initial
operation when the power supply is
turned on after off?
Check the power cable, power
switch, and terminal board, and
repair any defective part.
Check the indoor/outdoor unit
connection cable, and correct any
defective section (wrong connection,
incomplete insertion).
Is AC230V being generated between
terminals A and B on the outdoor unit
terminal board?
Is DC35V or 20V being generated
between terminals C and D on the
indoor unit terminal board?
Is the microcomputer reset input (pin7)
"Hi"?
Is the microcomputer clock signal
10MHz at pins 10 and 11 being
generated normally?
Is DC35V is being generated between
terminals C and D on the outdoor unit
terminal board?
Are C and D connection cables
reversed?
Connect the cables correctly.
Check the wireless light receiving unit.
Replace the control P.W.B.
Perform final operation check.
*1: When not in operation, the unit will enter into a low-power standby state, possibly causing a voltage drop to the 12V and 35V lines
as shown below.
25V - 20V
12V - 7V
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
CHECKING THE INDOOR UNIT ELECTRICAL PARTS
RAS_25_35_AW_087-108 2003.12.31, 10:59 AM 96