Mitsubishi Electric PLA-A12EA8 Service Manual page 20

Check code Abnormal point and detection method
Pipe temperature
<Cooling mode>
Detected as abnormal when the pipe tem-
perature is not in the cooling range 3 min-
utes after compressor start and 6 minutes
after the liquid or condenser/evaporator
pipe is out of cooling range.
Note 1: It takes at least 9 minutes to detect.
Note 2: Abnormality P8 is not detected in
drying mode.
Cooling range: −5.4°F [−3°C] ] (TH−TH1)
TH: Lower temperature between liquid pipe
temperature (TH2) and condenser/
evaporator temperature (TH5)
TH1: Intake temperature
<Heating mode>
When 10 seconds have passed after the
P8
compressor starts operation and the hot
adjustment mode has finished, the unit is
detected as abnormal when condenser/
evaporator pipe temperature is not in heat-
ing range within 20 minutes.
Note 3: It takes at least 27 minutes to
detect abnormality.
Note 4: It excludes the period of defrosting.
(Detection restarts when defrosting
mode is over.)
Heating range: 5.4°F [3°C] [ (TH5−TH1)
Pipe temperature thermistor/Condensor-
Evaporator (TH5)
1 The unit is in 3-minute resume protec-
tion mode if short/open of thermistor is
detected. Abnormal if the unit does not
get back to normal within 3 minutes. (The
unit returns to normal operation, if it has
been reset normally.)
2 Constantly detected during cooling,
drying, and heating operation (except
defrosting)
Short: 194°F [90:] or more
P9
Open: −40°F [−40:] or less
TCH120A
Cause
1 Slight temperature difference
between indoor room
temperature and pipe <liquid
or condenser/evaporator>
temperature thermistor
• Shortage of refrigerant
• Disconnected holder of pipe
<liquid or condenser/
evaporator> thermistor
• Defective refrigerant circuit
2 Converse connection of
extension pipe (on plural units
connection)
3 Converse wiring of indoor/
outdoor unit connecting wire (on
plural units connection)
4 Defective detection of indoor
room temperature and pipe
<condenser/evaporator>
temperature thermistor
5 Stop valve is not opened
completely.
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 Temperature of thermistor is
194°F [90:] or more or −40°F
[−40:] or less caused by
defective refrigerant circuit.
5 Defective indoor controller
board
20
Countermeasure
1–4 Check pipe <liquid or condenser/
evaporator> temperature with room
temperature display on remote con-
troller and outdoor controller circuit
board.
Pipe <liquid or condenser/evapora-
tor> temperature display is indicated
by setting SW2 of outdoor controller
circuit board as follows.
(
Conduct temperature check with outdoor
controller circuit board after connecting
'A-Control Service Tool(PAC-SK52ST)'.
23Check converse connection of exten-
sion pipe or converse wiring of indoor/
outdoor unit connecting wire.
1–3 Check resistance value of thermistor.
For characteristics, refer to (P1).
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 Operate in test run mode and check pipe
<condenser/evaporator> temperature with
outdoor controller circuit board. If pipe
<condenser/evaporator> temperature is
extremely low (in cooling mode) or high (in
heating mode), refrigerant circuit may have
defect.
5 Operate in test run mode and check pipe
<condenser/evaporator> temperature with
outdoor control circuit board. If there is
extreme difference with actual pipe
<condenser/evaporator> temperature,
replace indoor controller board.
There is no abnormality if none of above
(
comes within the unit.
Turn the power off and on again to operate.
In case of checking pipe temperature with outdoor
controller circuit board, be sure to
connect A-control service tool (PAC-SK52ST).
(
(