Abnormal Operation Of The Thermistor For The Indoor Unit Heat Exchanger Liquid Pipe Temperature (Freeze Protection Thermistor) - Hitachi RAS-(3-6)HVNC1(E) Service Manual

8 Troubleshooting
13
Alarm code
- 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 THM3 (freeze protection con-
Phenomenon
Faulty freeze protection
thermistor
Faulty PCB

Examples
Freeze protection thermis-
tor (THM3) in case of 4-way
cassette
242
SMGB0087 rev.0 - 12/2013
Abnormal operation of the thermistor for the indoor unit heat exchanger liquid pipe temperature
(freeze protection thermistor)
nected to I.U. of PCB?
Yes
Is the resistance of THM3
between 0.24kΩ and 840kΩ?
Yes
Faulty PCB
Cause
Fault
Incorrect connection
Thermistor characteristics
Thermistor
resistance
(kΩ)
Liquid Pipe Thermistor
(THM3)
No
Connect it
No
Faulty thermistor
Refer to the thermistor
resistance in Alarm 11
Check item
Check the resistance
Check the connection
Replace PCB and check the
operation
Air temperature (ºC)
Liquid Pipe Thermistor
(Freeze Protection)
Action
(Turn OFF the main switch)
Replace the thermistor if faulty
Repair the wiring and
connections
Replace PCB if faulty
Liquid Pipe Thermistor
(Freeze Protection)