Hitachi RAS-(4-12)HNP(1)(E) - Abnormal Operation of the Thermistor for the Evaporating Temperature During the Heating Process (Outdoor Unit)

8 Troubleshooting
250
SMGB0087 rev.0 - 12/2013
Alarm code
24
Abnormal operation of the thermistor for the evaporating temperature during the heating process
(outdoor unit)
• The RUN LED ickers 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 outdoor unit PCB. (*1)
If you nd an abnormal operation of the thermistor, check all the thermistors as shown below.
- The evaporating thermistor during the heating process is attached to the heat exchanger as shown in the gure
below. If this the thermistor is faulty, such as short-circuit (less than 0,2kΩ) or cut (more than 500kΩ) during opera-
tion, this alarm is displayed. The position is indicated below.
Is the thermistor THM8 (Te)
connected to PCB1?
Connect it
No
Yes
Is the resistance of THM8
between 0.2kΩ and 500kΩ?
Faulty thermistor
No
Yes
Faulty PCB1
Thermistor
(evaporating
temperature for
outdoor unit)
Phenomenon Cause Check item
Action
(Turn OFF the main switch)
Faulty thermistor for the
evaporating 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)
Ambient and evaporating temperature thermistor characteristics
for outdoor unit
Thermistor resistance (kΩ)
90
80
70
60
50
40
30
20
10
0
-15 -10 -5 0 5 10 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