Mitsubishi Electric SLZ Series Technical & Service Manual page 18

8-3. SELF-DIAGNOSIS ACTION TABLE
Check code
Abnormal point and detection method
Room temperature thermistor (TH1)
1The 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 minutes.
(The unit returns to normal operation, if it
has been reset normally.)
2 Constantly detected during cooling, drying
and heating operation
P1
Short: 194°F or more
Open: -40°F or less
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
minutes. (The unit returns to normal
operation, if it has been reset normally.)
2 Constantly detected during cooling,
drying, and heating (except defrosting)
P2
operation.
Short: 194°F or more
Open: -40°F or less
Contact failure of drain float switch
(CN4F)
• Extract when the connector of drain float
switch is disconnected.
P4
(3 and 4 of connector CN4F is not short-
circuited.)
• Constantly detected during operation
Drain overflow protection operation
1 Suspected abnormality, if drain float
switch is detected to be underwater for 1
minute and 30 seconds continuously with
drain pump on.
Compressor and indoor fan will be turned
off.
2 Drain pump is abnormal if the condition
above is detected during suspensive
abnormality.
P5
Constantly detected during drain pump
operation
OCH669A
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's service manual
for the details.
Cause
1 Defective thermistor
characteristics
2 Contact failure of connector
(CN20) on the indoor controller
board (Insert failure)
Breaking of wire or contact
failure of thermistor wiring
Defective indoor controller board
1 Defective thermistor
characteristics
2 Contact failure of connector
(CN44) on the indoor controller
board (Insert failure)
Breaking of wire or contact
failure of thermistor wiring
Defective refrigerant circuit is
causing thermistor temperature
of 194°F or more or -40°F or
less.
Defective indoor controller board
1 Contact failure of connector
(Insert failure)
2 Defective indoor controller
board
1 Malfunction of drain pump
2 Defective drain
Clogged drain pump
Clogged drain pipe
3 Defective drain float switch
Jamming of the drain float
switch or malfunction of moving
parts causing the drain float
switch to be detected under
water (Switch closed)
Defective indoor controller board
18
Countermeasure
1–
Check resistance value of thermistor.
30°F .....
50°F .......
70°F .......
90°F .......
100°F .....
If you put force on (draw or bend) the lead wire with
measuring resistance value of thermistor, breaking
of wire or contact failure can be detected.
2 Check contact failure of connector (CN20)
on the indoor controller board. Refer to "8-5.
TEST POINT DIAGRAM". Turn the power back
on and check restart after inserting connector
again.
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 checking.
– 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 "8-5.
TEST POINT DIAGRAM". Turn the power on
and check restart after inserting connector
again.
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 defect.
Check pipe <liquid> temperature with remote
controller in test run mode. If there is extreme
difference with actual pipe <liquid> temperature,
replace indoor controller board.
Turn the power off, and on again to operate
after checking.
1 Check contact failure of float switch connector.
Turn the power on again and check after
inserting connector again.
2 Operate with connector (CN4F) short-
circuited.
Replace indoor controller board if abnormality
reappears.
1 Check if drain pump works.
2 Check drain function.
3 Remove drain float switch connector CN4F
and check if it is short (Switch closed) with the
moving part of float switch UP, or OPEN with
the moving part of float switch down.
Replace float switch if it is closed with the
moving part of float switch down.
4 Replace indoor controller board if it is short-
circuited between 3–4 of the drain float
switch connector CN4F and abnormality
reappears.
It is not abnormal if there is no problem about
the above-mentioned 1–4.
Turn the power off, and on again to operate after
check.