Hitachi RAC-25YH4, Service Manual, Page: 76 / 121

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• The voltage specification of the power circuit is as follows.
<Check points>
Output Voltage Main load Measuring points Potential failure modes
spec. + –
12V 11-13V MAIN P.W.B. (CN3, CN4) R701 (“12V” display) R006 (“0V” display) The unit won’t operate
C21 (“12V” display) J27, J30 MAIN P.W.B. error
5V 4.5-6V MAIN P.W.B. (CN3, CN4) D30 anode (“5V” display) R006 (“0V” display) The unit won’t operate
J25 J27, J30 MAIN P.W.B. error
B-12V 11-16V Expansion valve R25 (“B-12V” display) R25 (“B-0V” display) LD301 blinks 5 times;
Expansion valve error
15V 14-17V DC fan motor (CN24) C06+ side C06- side LD301 blinks 3 times,
MAIN P.W.B. (CN3, CN4)
35V 33.5-38V Indoor unit electrical parts D20 cathode J5, j17 Indoor unit won’t operate
(Terminal C,D) (“C-35V” display) Terminal D (red line)
Reversing valve (CN2) Terminal C (blown line)
• Check each voltage. If each voltage meets the voltage specification above, the power circuit is normal.
• If any error is found after checking, remove all loads and recheck each voltage.
If no error is found in this step, the power circuit is normal. Check the removed loads.
If any error is found in this step, the power circuit has any failure. Replace the power P.W.B.
* A short-circuited load may cause an output error not only in the load but also in the others. Be sure to
check all outputs of the loads.
* Be sure to wait 15 minutes or more in order to discharge all the remaining voltage in the circuit to
connect/disconnect the wiring, other wise, the components may be damaged.
•
The failures of the loads are as follows.
Failed
output
35V
15V
12V, 5V
Criterion
Connect the cable correctly.
Remove the connection cable and measure the
voltage. If the voltage is correct, check the electrical
parts for the indoor unit.
Remove the CN2 and measure the voltage. If the
voltage is correct, check the reversing valve.
Remove the CN24 and measure the voltage.
(connect the CN3.) If the voltage is correct, check
the DC fan motor.
Also, check the main P.W.B 1 A fuse for blow out in
this step.
Remove the CN3 and CN4 and meaure the voltage.
If the voltage is correct, check the main P.W.B.
Remove the CN3 and CN4 and meaure the voltage.
If the voltage is correct, check the main P.W.B.
Possible causes
Reversed connection of the cable.
Electrical part for the indoor unit has
a failure.
Short-circuited reversing valve
DC fan motor error
Main P.W.B. error
Main P.W.B. error
RAS_25_35_AW_055-086 2003.12.31, 10:59 AM 74