Hitachi UTOPIA RAS-4HVRP2E - Page 249

10 Troubleshooting
Troubleshooting procedure
SMGB0136 rev.0 - 07/2021
247
10
Alarm code
20
Abnormality of thermistor for discharge gas temperature (compressor
thermistor)
• This alarm code is indicated when the thermistor is short-circuited (less than 1 kΩ) or cut (higher than 640 kΩ)
during the cooling or the heating process.
• This alarm forces all operations to stop (Outdoor & Indoor Units).
• The unit should be stopped to release the alarm.
Is the thermistor connected to
THM9 of PCB?
Connect it
No
Yes
Is the resistance of THM9
between1kΩand6kΩ?
Faulty thermistor
No
Yes
Faulty PCB
Thermistor on top of
compressor
Phenomenon Cause Check item
Action
(Turn OFF the main switch)
Faulty top of compressor
thermistor
Fault Check resistance Replace thermistor if faulty
Incorrect connection Check wiring to PCB1 Repair wiring and connections
Faulty PCB1
Replace PCB1 and check
operation
Replace PCB1 if faulty
1072,0
640,4
394,2
249,2
161,5
107,0
72,3
50,0
35,1
25,1
18,2
13,4
9,9
7,5
6,5
0
200
400
600
800
1000
1200
-100 10 20 30 40 50 60 70 80 90 100110 120130
Thermistor resistance characteristics
Temperature (ºC)
Thermistorresistance(kΩ)