Hitachi RAS-(4-12)HNP(1)(E) - Abnormal Operation of the Thermistor for the Indoor Discharge Air Temperature (Air Outlet Thermistor)

8 Troubleshooting
241
SMGB0087 rev.0 - 12/2013
8
Alarm code
12
Abnormal operation of the thermistor for the indoor discharge air temperature (air outlet thermistor)
- 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 THM2 (outlet air) connected
I.U. PCB?
Connect it
No
Yes
Is the resistance of THM2
between 0.24kΩ and 840kΩ?
Faulty thermistor
No
Yes
Faulty PCB
Phenomenon Cause Check item
Action
(Turn OFF the main switch)
Faulty air outlet thermistor
Fault Check the resistance Replace the thermistor if faulty
Incorrect connection Check the connection
Repair the wiring and
connections
Faulty PCB
Replace PCB and check the
operation
Replace PCB if faulty
Thermistor
resistance
(kΩ)
Air temperature (ºC)
Thermistor characteristics

Examples
Indoor unit air inlet
thermistor (THM2)
in case of 4-way
cassette
Outlet Air Thermistor
Outlet Air Thermistor
Outlet Air Thermistor