11 Maintenance notes
General notes
SMGB0091 rev.2 - 11/2015
286
11.1.5 Alarm code “31”
Question and answer for the field work
Example 4: Alarm code "31"
Phenomenon
Alarm code "31" sometimes occurred and the system stopped.
Cause
The combination of the indoor units and the RASC unit was the following.
Power source
RASC unit
Indoor unit
Indoor unit
Indoor unit
Indoor unit
The system was used in a tenant building. One of tenants’ costumers turned off the main switch for the indoor
unit while other indoor units were running. This resulted in a different setting of total indoor unit capacity in the
same refrigerant cycle, causing abnormal working conditions. When the capacity of the system dropped under
the minimum value, alarm 31 was activated putting the system in Thermo-OFF.
Countermeasure
To set the main switch of the indoor units to be always ON, or to install the Hitachi Multitenant building
connection board PC-AMTB.
11.1.6
Not cooling well due to insufficient installation space for the RASC unit
Question and answer for the field work:
Example 5: Not cooling well due to insufficient installation space for RASC unit or inlet/outlet air bypass
Phenomenon
Cooling operation was well performed through the intermediate season. However, the cooling operation was
not well available when the outdoor temperature was higher than 35ºC.
Cause
Hot discharge air re-circulation.
In this case, though the outdoor temperature was 35ºC, the actual suction air temperature was nearly 50ºC
and protection system from excessively high suction pressure was activated, the frequency of the compressor
was decreased and the cooling capacity was also decreased accordingly.
Countermeasure
Ensure that inlet and outlet is not bypassed (use grilles in opposite directions if necessary).
Ensure that inlet and outlet air in opened spaces (never near walls).