Remote Controller Temperature Thermistor Anomaly - Mitsubishi Heavy Industries FDT Series Technical Manual

Error code
E28
Remote controller:
1. Applicable model
All models
2. Error detection method
Detection of anomalously low
temperature (resistance) of
remote controller temperature
thermistor (Thc)
3. Condition of Error displayed
When the temperature
thermistor detects -50°C
or lower for 5 seconds
continuously, the compressor
stops. After 3-minutes delay,
the compressor starts again
automatically, but if this error
occurs again within 60 minutes
after the initial detection.
4. Presumable cause
• Faulty connection of remote
controller temperature
thermistor
• Defective remote controller
temperature thermistor
• Defective remote controller
PCB
Note:
After 10 seconds has passed since remote controller thermistor was switched from valid to invalid, E28 will not be displayed even if the
thermistor harness is disconnected. At same time the thermistor, which is effective, is switched from remote controller thermistor to indoor return
air temperature thermistor. Even though the remote controller thermistor is set to be Effective, the return air temperature displayed on remote
controller for checking still shows the value detected by indoor return air temperature thermistor, not by remote controller temperature thermistor.
LED Green Red
Stays OFF
Indoor
Stays OFF
Outdoor
5. Troubleshooting
Diagnosis
Is the remote
controller temperature thermistor
connected properly?
YES
Are the
characteristics of
remote controller temperature
thermistor OK?
Is the thermistor wire
OK?
Resistance-temperature characteristics of remote controller temperature thermistor (ThC)
Temperature (°C) Resistance value (k )
0
1
2
4
6
8
10
12
14
16
18
20
22
24
26
28
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Content
Remote controller
temperature thermistor anomaly
NO
NO
YES
Temperature (°C)
65 30
62 32
59 34
53 36
48 38
44 40
40 42
36 44
33 46
30 48
27 50
25 52
23 54
21 56
19 58
18 60
-
'12 • PAC-T-173
Countermeasure
Correct.
Defective remote controller
temperature thermistor
Replace.
Defective remote controller
PCB Replace.
(Defective remote
controller temperature
thermistor input circuit)
Resistance value (k )
16
15
14
13
12
11
9.9
9.2
8.5
7.8
7.3
6.7
6.3
5.8
5.4
5.0