Abnormally High Operation Sound (In The Ceiling Type Indoor Unit); Alarm Code "31; Not Cooling Well Due To Insufficient Installation Space For The Outdoor Unit - Hitachi UTOPIA RAS-4HVRP2E Service Manual

11 Maintenance notes
General notes

11.1.4 Abnormally high operation sound (in the ceiling type indoor unit)

Question and answer for the field work
Example 3: Abnormally high operation sound (in-the-ceiling type indoor unit)
Phenomenon The operation sound at the "HIGH" speed was abnormally high.
The indoor units were installed without the ducts. Since there was any external static pressure a big air
volume was supplied. This resulted in a higher air speed through the heat exchanger.
Cause
Countermeasure In order to reduce the airflow set the indoor unit at "Low static pressure" setting.

11.1.5 Alarm code "31"

Question and answer for the field work
Phenomenon
Alarm code "31" sometimes occurred and the system stopped.
The combination of the indoor units and the outdoor unit was the following.
Cause
This system was used in a tenant building. One of the tenant's customers turned OFF the main switch for the
indoor unit while other indoor units are running. This results in a different setting of the total indoor unit capacity in
the same refrigerant cycle.
Countermeasure All the main switches for the indoor units were always ON.

11.1.6 Not cooling well due to insufficient installation space for the outdoor unit

Question and answer for the field work
Example 5: Not cooling well due to insufficient installation space for outdoor unit
Cooling operation was well performed through the intermediate season. However the cooling operation was not
Phenomenon
well available when the outdoor temperature was higher than 35 °C.
As the outdoor units were installed without a sufficient installation space the hot discharge air from other outdoor
units was circulated.
In this case though the outdoor temperature was 35 °C the actual suction air temperature was nearly 50 °C and
Cause protection system from excessively high suction pressure was activated the frequency of the compressor was
decreased and the cooling capacity was also decreased accordingly.
As the outdoor units in-line were installed back to back with a certain distance between each outdoor unit's back
the hot discharged air from other outdoor units was circulated.
Countermeasure
Ensure that sufficient space should be secured for multi-row and multiple-installation.
325 SMGB0136 rev.0 - 07/2021
Damper
Example 4: Alarm code "31"
ON
Power Power
source
OFF
Source ON ON OFF
Indoor unit
Air filter
ON
ON
ON ON ON ON ON
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