Mitsubishi Electric PLA-A12EA8 Service Manual page 18

9-3. SELF-DIAGNOSIS ACTION TABLE
Check code Abnormal point and detection method
Room temperature thermistor (TH1)
1 The unit is in 3-minute resume
prevention mode if short/open of
thermistor is detected. Abnormal if the
unit does not reset normally after 3 min-
utes. (The unit returns to normal opera-
tion, if it has been reset normally.)
2 Constantly detected during cooling,
drying, and heating operation.
Short: 194°F [90:] or more
Open: −40°F [−40:] or less
P1
Pipe temperature thermistor/liquid (TH2)
1 The unit is in 3-minute resume
prevention mode if short/open of
thermistor is detected. Abnormal if the
unit does not reset normally after 3 min-
utes. (The unit returns to normal opera-
tion, if it has been reset normally.)
2 Constantly detected during cooling,
drying, and heating (except defrosting)
operation
Short: 194°F [90:] or more
P2
Open: −40°F [−40:] or less
Contact failure of drain float switch
(CN4F)
• Extract when the connector of drain float
switch is disconnected.
(3 and 4 of connector CN4F is not
short-circuited.)
P4
• Constantly detected during operation
TCH120A
Note:
Errors to be detected in outdoor unit, such as codes starting with F, U or E (excluding E0 to E7),
are not covered in this document. Please refer to the outdoor unit service manual for the details.
Cause
1 Defective thermistor
characteristics
2 Contact failure of connector
(CN20) on the indoor controller
board (Insert failure)
3 Breaking of wire or contact
failure of thermistor wiring
4 Defective indoor controller
board
1 Defective thermistor
characteristics
2 Contact failure of connector
(CN44) on the indoor controller
board (Insert failure)
3 Breaking of wire or contact
failure of thermistor wiring
4 Defective refrigerant circuit is
causing thermistor temperature
of 194°F [90:] or more, or
−40°F [−40:] or less.
5 Defective indoor controller
board
1 Contact failure of connector
(Insert failure)
2 Defective indoor controller
board
18
Countermeasure
1–3 Check resistance value of thermistor.
32°F [0:] ....15.0 k"
50°F [10:] ......9.6 k"
68°F [20:] ......6.3 k"
86°F [30:] ......4.3 k"
104°F [40:] ......3.0 k"
If you put force on (draw or bend) the lead
wire with measuring resistance value of
thermistor, breaking of wire or contact fail-
ure can be detected.
2 Check contact failure of connector (CN20)
on the indoor controller board. Refer to
"9-7. TEST POINT DIAGRAM".
Turn the power on again and check
restart after inserting connector again.
4 Check room temperature display on
remote controller.
Replace indoor controller board if there
is abnormal difference with actual room
temperature.
Turn the power off, and on again to operate
after check.
1–3 Check resistance value of thermistor.
For characteristics, refer to (P1) above.
2 Check contact failure of connector (CN44)
on the indoor controller board. Refer to
"9-7. TEST POINT DIAGRAM".
Turn the power on and check restart
after inserting connector again.
4 Check pipe <liquid> temperature with
remote controller in test run mode. If pipe
<liquid> temperature is extremely low (in
cooling mode) or high (in heating mode),
refrigerant circuit may have defective.
5 Check pipe <liquid> temperature with
remote controller in test run mode. If
there is extremely difference with actual
pipe <liquid> temperature, replace indoor
controller board.
Turn the power off, and on again to operate
after check.
1 Check contact failure of float switch con-
nector.
Turn the power on again and check after
inserting connector again.
2 Operate with connector (CN4F) short-circuited.
Replace indoor controller board if abnormality reap-
pears.