Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 321

[ IX Troubleshooting ]
Phenomena
2 Although heating operation
starts with the normal remote
controller display, the capacity
is not enough.
Cause
1. Compressor frequency does not
rise sufficiently.
Faulty detection of pressure
sensor.
Protection works and compres-
sor frequency does not rise due
to high discharge temperature
Protection works and compres-
sor frequency does not rise due
to high pressure.
2. Indoor unit LEV malfunction
Insufficient refrigerant flows due
to LEV malfunction (not enough
opening).
3. When the higher temperature
than the actual temperature is de-
tected due to malfunction of the
piping sensor (TH22) on the in-
door unit, the smaller sub cool is
detected, and LEV opening will be
smaller.
4. RPM error of the outdoor unit FAN
Motor failure or board failure, or
airflow rate decrease, pressure
drop due to clogging of the heat
exchanger leading to high dis-
charge temperature
The fan is not properly controlled
as the temperature cannot be
precisely detected with the pip-
ing sensor.
- 312 -
Check method and remedy
(1) Check pressure difference between the
detected pressure by the pressure sen-
sor and the actual pressure with self-di-
agnosis LED.
-> If the accurate pressure is not de-
tected, check the pressure sensor.(Re-
fer to the page on Troubleshooting of
Pressure Sensor)
Note: Higher inlet pressure by the high
pressure sensor than the actual
pressure causes insufficient ca-
pacity.
SW1 setting
High pressure sensor
1 2 3 4 5 6 7 8 9 10
ON
Low pressure sensor
1 2 3 4 5 6 7 8 9 10
ON
(2) Check the difference between the con-
densing temperature (Tc) and the tar-
get condensing temperature (Tcm) with
self-diagnosis LED.
Note: Higher Te than Tem causes in-
sufficient capacity.
SW1 setting
Condensing temperature Tc
1 2 3 4 5 6 7 8 9 10
ON
Target condensing temperature Tcm
1 2 3 4 5 6 7 8 9 10
ON
Protection works and compressor fre-
quency does not rise even at lower
Tc than Tcm due to high discharge
temperature and high pressure.
At high discharge temperature:
Refer to 1102
At high pressure: Refer to 1302
Refer to the page of LEV troubleshooting (9.
[4]. -6- ).
Check the thermistor (TH22).
Refer to the page on outdoor unit fan ([4] -4-
).