Hitachi UTOPIA RAS-4HVRP2E - Page 251

10 Troubleshooting
Troubleshooting procedure
SMGB0136 rev.0 - 07/2021
249
10
Alarm code
24
Abnormal operation of the thermistor for the evaporating temperature during the
heating process (outdoor unit) (THM8/THM10)
- The evaporating / condensing thermistor during the heating process is attached to the heat exchanger as shown
inthegure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?
Connect it
No
Yes
Is the resistance of THM8 /
THM10between0.2kΩand500
kΩ?
Faulty thermistor
No
Yes
Faulty PCB1
Evaporating
temperature
thermistor for
outdoor unit
(THM8)
Phenomenon Cause Check item
Action
(Turn OFF the main switch)
Faulty thermistor for the
evaporating / condensing
temperature during
heating
Fault Check the resistance Replace the thermistor if faulty
Incorrect Connection Check the wiring to PCB
Repair the wiring and the
connections
Faulty PCB
Replace PCB and check the
operation
Replace PCB if faulty
Ambient temperature (ºC)
Thermistorresistance(kΩ)
90
80
70
60
50
40
30
20
10
0
-15 -10 -5 0510 15 20 25 30 35 40 45 50 55 60
74
43
33
26
20
16
12.5
10
8
5.3
3.6
2.5
56
THM8 (Evaporating thermistor)
80
70
60
50
40
30
20
10
0
-15 -10 -5 0510 15 20 25 30 35 40 45 50 55 60
26.0
20.2
15.9
12.6
10.0
8.05
5.31
3.60
2.49
33.7
44.0
58.3
78.0
6.52
4.36
2.99
Ambient temperature (ºC)
Thermistorresistance(kΩ)
THM10 (Condensing thermistor)