Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 322

Phenomena
2 Although heating operation
starts with the normal remote
controller display, the capacity
is not enough.
3 Outdoor unit stops at times
during operation.
Cause
5. Insulation failure of the refrigerant
piping
6. Long piping length
Excessively long piping on the
high pressure side causes pres-
sure loss leading to increase in
the high pressure.
7. Piping size is not proper (thin)
8. Clogging by foreign object
9. The indoor unit inlet temperature
is excessively high.(exceeding
28°C [82°F])
10.Insufficient refrigerant amount
Protection works and compressor
frequency does not rise due to low
discharge temperature
Refrigerant recovery operation is
likely to start.
11.Compressor failure (same as in
case of cooling)
The first stop is not considered as an
error, as the unit turns to anti-restart
mode for 3 minutes as a preliminary
error.
Error mode
(i) Abnormal high pressure
(ii) Abnormal discharge air
temperature
(iii) Heatsink thermistor failure
(iv) Thermistor failure
(v) Pressure sensor failure
(vi) Over-current break
(vii) Refrigerant overcharge
Note: Frost prevention tripping only
under cooling mode may be
considered in addition to the
above. (Freeze protection is
detected by one or all indoor
units.)
Note: Even the second stop is not
considered as an error
when some specified errors
occur. (eg. The third stop is
considered as an error
when the thermistor error
occurs.)
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[ IX Troubleshooting ]
Check method and remedy
Confirm that the characteristic of capacity
drop due to piping length.
-> Change the pipe
Check the temperature difference between
in front of and behind the place where the
foreign object is clogging the pipe (up-
stream side and downstream side). Difficult
to confirm if the object is clogged inside the
extended piping. Run the unit in cooling
mode, and find the foreign object using the
same method as that for cooling operation.
-> Remove the foreign object.
Check the inlet air temperature and for short
cycling. Change the environment where the
indoor unit is used.
Refer to 2 - 1. (Compressor frequency does
not rise sufficiently.)
Refer to the page on refrigerant amount ad-
justment
Check the discharge temperature.
(1) Check the mode operated in the past
by displaying preliminary error history
on LED display with SW1.
(2) Reoperate the unit to find the mode that
stops the unit by displaying preliminary
error history on LED display with SW1.
Refer to the reference page for each er-
ror mode.
*Display the indoor piping temperature
table with SW1 to check whether the
freeze proof operation runs properly,
and check the temperature.