Hitachi FS3 Series, Service Manual, Page: 232 / 240

5
2
FIELD WORK INSTRUCTION
5.3. ABNORMALLY HIGH OPERATING SOUND (IN-THE-CEILING TYPE INDOOR UNIT)
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Question and Answer for Field Work
Example 3: Abnormally High Operating Sound (In-the-Ceiling Type Indoor Unit)
Phenomenon Operating sound during "Hi" speed was abnormally high.
Cause
The indoor units was installed without ducts. Due to almost no external static pressure,
abnormally big air volume was supplied, resulting in higher air speed through the heat
exchanger.
Countermeasure In order to reduce air flow, a plate as a damper at the discharge side was added.
Remarks Please note that running current is increased when no external pressure is given to the
indoor unit, resulting in overheating.
5.4. ALARM CODE "31"
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Question and Answer for Field Work
Example 4: Alarm Code "31"
Phenomenon Alarm code "31" sometimes occurred and the system was stopped.
Cause Combination of the indoor and outdoor unit was as follows.
This system was used in a tenant building. One of tenant’s customers cut out the power
switch for the indoor unit while other indoor units are running, resulting in different total indoor
unit capacity setting in the same refrigerant cycle.
Countermeasure All the main power switches for the indoor units were always ON.
Indoor Unit
Damper
A. Filter
ON
ON
OFF
I.U.
ON
I.U.
ON
I.U.
ON
O.U.
Power
Source