Hitachi RASC-4HNPE Service Manual page 232

10 Troubleshooting
Troubleshooting procedure
15
Alarm code
• The RUN LED flickers and "ALARM" is displayed on the remote control switch.
• The unit number, the alarm code and the unit code are alternately displayed on the set temperature section. The unit
number and the alarm code are displayed on the display of the RASC unit PCB.
- This alarm code is displayed when the thermistor is short-circuited (less than 0.24 kΩ) or cut (greater than 840 kΩ)
during the cooling process or the heating process. The system is automatically restarted when the fault is removed.
Is THM4 connected to (intake)
between 0.24kΩ and 840kΩ?
Phenomenon
Faulty fresh outdoor air
(Econofresh) thermistor
Faulty PCB
222 SMGB0091 rev.2 - 11/2015
Abnormal operation of thermistor for fresh outdoor air (Econofresh)
of PCB?
Yes
Is the resistance of THM4
Yes
Faulty PCB
Cause
Fault
Incorrect connection
Thermistor
resistance
(kΩ)
Thermistor characteristics
No
Connect it
No
Faulty thermistor
Check item
Check the resistance
Check the connection
Replace PCB and check the
operation
Air temperature (°C)
Action
(Turn OFF the main switch)
Replace the thermistor if faulty
Repair the wiring and
the connections
Replace PCB if faulty