Mitsubishi Electric PU-2NJA Technical & Service Manual page 14

Check
Diagnosis of malfunction
code
(P1) Abnormality of room temper-
ature thermistor (RT1)
(P2) Abnormality of indoor coil
thermistor (RT2)
(P4) Abnormality of drain sensor
(P5) Malfunction of drain pump
(P6) Coil frost protection is work-
ing.
(P8) Abnormality in outdoor unit
Cause
1) Bad contact of thermistor
2) Damaged thermistor
1) Bad contact of transmission
wire
2) Damaged thermistor
1) Malfunction of drain pump
2) Damaged drain sensor
1) Short cycle of air cycle
2) Dirty air filter
3) Damaged fan
4) Abnormal refrigerant
1) Wrong wiring of indoor/outdoor
connecting wire
2) Reversed phase
3) Protection device is working
4) Damaged outdoor coil thermis-
tor
14
Check points
1) Check the thermistor.
2) Measure the resistance of the thermistor.
Normal resistance should be as follows.
0°C ···15kΩ 30°C ····4.3kΩ
10°C ·····9.6kΩ 40°C·····3.0kΩ
20°C ·····6.3kΩ
If the resistance is normal, replace the indoor
controller board.
1) Check the connector.
2) Measure the resistance of the thermistor 4 ~
5.
As for the normal resistance, refer to the case
of P1.
If the resistance is normal, replace the indoor con-
troller board.
1) Check the drain pump.
2) Check the drain sensor.
Check the drain sensor heater. Normal resis-
tance should be 82Ω.
If the resistance is normal, replace the indoor con-
troller board.
1) Clear obstructions from the air cycle.
2) Clean the air filter
3) Check the fan.
4) Check the refrigerant temperature.
1) Check the indoor/outdoor connecting wire.
2) Change the connection of electric wiring.
3) Check the protection device.
4) Measure the resistance of the outdoor coil ther-
mistor. If the resistance is normal, replace the
outdoor controller board.