Abnormal Operation Of The Thermistor For The Outdoor Temperature (Outdoor Unit Ambient Thermistor) - Hitachi RAS-(3-6)HVNC1(E) Service Manual

8 Troubleshooting
22
Alarm code
• The RUN LED flickers 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.
- This alarm code is displayed when the thermistor is short-circuited (less than 0.2 kΩ) or cut (greater than 500 kΩ)
during the operation.
Is the thermistor (THM7: red)
connected to PCB1?
Is the resistance of THM7
between 0.24kΩ and 500kΩ?
Faulty PCB1
90
80
74
70
60
56
50
43
40
33
30
20
10
0
-15 -10 -5 0
Phenomenon
Faulty thermistor for the out-
door unit ambient
Faulty PCB1
249
SMGB0087 rev.0 - 12/2013

Abnormal operation of the thermistor for the outdoor temperature (outdoor unit ambient thermistor)

No
Yes
No
Yes
Thermistor characteristics
26
20
16 12.5
10
8
5.3
5 10 15 20 25 30 35 40
Ambient temperature (ºC)
Cause
Fault
Incorrect connection
Outdoor temperature thermistor
Connect it
Faulty thermistor
Outdoor temperature thermistor
Other than above
3.6
2.5
45 50 55 60
Check item
Check resistance
Check wiring to PCB
Replace PCB1 and check
operation
RAS-2/2.5HVNP
RAS-3HVNC
Action
(Turn OFF Main Switch)
Replace thermistor if faulty
Repair wiring and connections
Replace PCB if faulty
8