Mitsubishi Electric Mr. SLIM PCA-M71HA2 Service Manual page 14

9-3. SELF-DIAGNOSIS ACTION TABLE
Check Code Abnormal point and detection method
Room temperature thermistor (TH1)
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.)
Constantly detected during cool, dry,
and heat operation.
Short: 90˚C or more
Open: −40˚C or less
P1
Pipe temperature thermistor/Liquid
(TH2)
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.)
Constantly detected during cool, dry,
and heat (except defrost) operation
P2
Short: 90˚C or more
Open:−40˚C or less
Freezing/overheating protection is
operating
Freezing protection (Cool mode)
The unit is in 6-minute resume preven-
tion mode if pipe <liquid or condenser/
evaporator> temperature stays under
−15°C for 3 minutes, 3 minutes after
the compressor started. Abnormal if
it stays under −15°C for 3 minutes
again within 16 minutes after 6-minute
resume prevention mode.
P6
Overheating protection (Heat mode)
The units is in 6-minute resume
prevention mode if pipe <condenser/
evaporator> temperature is detected as
over 70°C after the compressor started.
Abnormal if the temperature of over
70°C is detected again within 30 min-
utes after 6-minute resume prevention
mode.
OCH753A
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
Defective thermistor
characteristics
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
Defective thermistor
characteristics
Contact failure of connector
(CN21) on the indoor controller
board (Insert failure)
Breaking of wire or contact
failure of thermistor wiring
Defective refrigerant circuit is
causing thermistor temperature
of 90˚C or more or −40˚C or
less.
Defective indoor controller
board
(Cool or dry mode)
Clogged filter (reduced airflow)
Short cycle of air path
Low-load (low temperature)
operation out of the tolerance
range
Defective indoor fan motor
• Fan motor is defective.
• Indoor controller board is defec-
tive.
Defective outdoor fan control
Overcharge of refrigerant
Defective refrigerant circuit (clogs)
(Heat mode)
Clogged filter (reduced airflow)
Short cycle of air path
Overload (high temperature)
operation out of the tolerance
range
Defective indoor fan motor
• Fan motor is defective.
• Indoor controller board is defective.
Defective outdoor fan control
Overcharge of refrigerant
Defective refrigerant circuit (clogs)
Bypass circuit of outdoor unit is
defective.
14
Judgment and action
– Check resistance value of thermistor.
0˚C ...15.0 kΩ
10˚C .... 9.6 kΩ
20˚C .... 6.3 kΩ
30˚C .... 4.3 kΩ
40˚C .... 3.0 kΩ
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.
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.
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.
– Check resistance value of thermistor.
For characteristics, refer to (P1) above.
Check contact failure of connector (CN21)
on the indoor controller board. Refer to "9-7.
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 cool mode)
or high (in heat mode), refrigerant circuit may
be defective.
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.
(Cool or dry mode)
Check clogs of the filter.
Remove blockage.
Refer to "9-6. HOW TO CHECK THE
PARTS".
Check outdoor fan motor.
Check operating condition of refrigerant
circuit.
(Heat mode)
Check clogs of the filter.
Remove blockage.
Refer to "9-6. HOW TO CHECK THE
PARTS".
Check outdoor fan motor.
– Check operating condition of refrigerant
circuit.