Hitachi UTOPIA RAS-4HVRP2E Service Manual page 251

10 Troubleshooting
Troubleshooting procedure
24
Alarm code
- The evaporating / condensing thermistor during the heating process is attached to the heat exchanger as shown
in the figure below. If this thermistor is faulty, such as short-circuit (less than 0,2kΩ) or cut (more than 500kΩ)
during eight minutes continuously, this alarm is displayed. The position is indicated below.
• This alarm forces all operations to stop (Outdoor & Indoor Units).
• The unit should be stopped to release the alarm.
Is the thermistor THM8 / THM10
connected to PCB1?
Yes
Is the resistance of THM8 /
THM10 between 0.2 kΩ and 500
kΩ?
Yes
Faulty PCB1
Phenomenon
Faulty thermistor for the
evaporating / condensing
temperature during
heating
Faulty PCB
90
80
74
70
60
56
50
43
40
33
30
26
20
20
16 12.5
10
0
-15 -10 -5 0 5 10 15
Ambient temperature (ºC)
THM8 (Evaporating thermistor)
249 SMGB0136 rev.0 - 07/2021
Abnormal operation of the thermistor for the evaporating temperature during the
heating process (outdoor unit) (THM8/THM10)
No
No
Faulty thermistor
Cause
Fault
Incorrect Connection
Replace PCB and check the
10
8
5.3
3.6
2.5
20 25 30 35 40 45 50 55 60
Connect it
Check item
Check the resistance
Check the wiring to PCB
operation
80
78.0
70
60
58.3
50
44.0
40
33.7
30
26.0
20.2
20
15.9
10
0
-15 -10 -5 0 5 10 15
Ambient temperature (ºC)
THM10 (Condensing thermistor)
Evaporating
temperature
thermistor for
outdoor unit
(THM8)
Action
(Turn OFF the main switch)
Replace the thermistor if faulty
Repair the wiring and the
connections
Replace PCB if faulty
12.6
10.0
8.05
6.52
5.31
4.36
3.60 2.99
20 25 30 35 40 45 50 55 60
10
2.49