Mitsubishi Electric PRH-P8MYA Technical & Service Manual page 69

<Abnormality detected during unit operation: Indoor-side unit>
Abnormal- Meaning of abnormality display and
ity display abnormality troubleshooting
Piping temperature abnormal
<Cool>
When the piping temperature stays
outside the cooling area for 1 minute
after 3 minutes have elapsed since
the compressor was started, the in-
door-side fan operates at low speed.
If the piping temperature does not
return to the cooling area after
5 minutes operation at low speed, an
abnormality is recognized.
Note 1) It takes a minimum of 9 min-
utes for an abnormality to be
detected.
Note 2) At dry operation, P8 abnor-
mality is not detected.
P8 <Heat>
When the piping temperature falls
outside the heating area and enters
the ventilation area after compressor
operation and the end of hot adjust,
the indoor-side fan stops and the
piping temperature does not
return to the heating area within
20 minutes after 10 seconds have
elapsed after it left the heating
area, an abnormality is recognized.
Note 3) It takes a minimum of 22
minutes and a maximum of
27 minutes for an abnormal-
ity to be detected.
Note 4) Except during defrosting
(Detected again after de-
frosting return.)
Piping (2-phase pipe) sensor
abnormal
1) If thermistor short or open is de-
tected and the compressor enters
the 3 minutes restart prevention
mode and does not return to nor-
mal after 3 minutes, an abnormal-
ity is recognized.
(If returned, returns to normal op-
eration.)
P9
2) Always detected during cool, dry,
and heat (except during defrost-
ing) operation.
Short: 90 °C or higher
Open: –40 °C or lower
Cause
(1) Indoor-side intake piping thermistor
temperature differential small.
- Insufficient refrigerant
- Piping thermistor holder dislodged.
- Refrigerant circuit faulty.
(2) Indoor-side intake piping thermistor
detection faulty.
(1) Thermistor characteristics faulty.
(2) Connector contact faulty.
(Insertion faulty)
(3) Thermistor wiring open or contact
faulty.
(4) Faulty refrigerant circuit, etc. has
caused thermistor temperature to rise
to 90 °C or higher or drop to –40 °C
or lower.
(5) Indoor-side controller board faulty.
- 66 -
Judgment method and remedy
(1) Operate in test run mode and check
piping temperature.
(2) Check remote controller room tempera-
ture display and piping temperature in
test run mode.
(1)-(3)
Check thermistor resistance value.
For characteristic, see page 41.
(2) Check for connector faulty contact.
After reinserting connector, turn on
power and recheck operation.
(4) Operate in trail run mode and check
piping temperature with remote control-
ler. When piping temperature is abnor-
mally low (cooling) or high (heating),
refrigerant circuit is probably faulty.
(5) Check test run mode piping tempera-
ture with remote controller.
If there is a difference between actual
piping temperature and displayed pip-
ing temperature when there are no ab-
normalities at (1)-(4), replace indoor
-side controller board. If there is no
problem above, there are no
abnormalities.
Turn on power and operate.