Mitsubishi Electric City Multi PQHY-P72 Service Handbook page 270

Phenomena
1 Although cooling operation
starts with the normal remote
controller display, the capacity
is not enough.
Cause
3. Long piping length
The cooling capacity varies great-
ly depending on the pressure
loss. (When the pressure loss is
large, the cooling capacity drops.)
4. Piping size is not proper (thin)
5. Insufficient refrigerant amount
Protection works and compressor
frequency does not rise due to
high discharge temperature.
6. Clogging by foreign object
7. The indoor unit inlet temperature
is excessively. (Less than 15°C
[59°F] WB
8. Compressor failure
The amount of circulating refriger-
ant decreases due to refrigerant
leak in the compressor.
9. LEV1 malfunction
Sufficient liquid refrigerant is not
be supplied to the heat source unit
as sufficient sub cool cannot be
secured due to LEV1 malfunction.
(PQHY only)
10.TH5, TH7 and HPS sensor fail-
ure or faulty wiring
LEV1 is not controlled normally.
(PQHY only)
11.BC controller LEV1 failure
Refrigerant flow in the indoor units
is retarded because the BC con-
troller LEV1 failure is causing the
loss of indoor unit pressure differ-
ential. (PQRY only)
12.BC controller HPS1, HPS2 sen-
sor failure, faulty wiring
BC controller LEV1 is not con-
trolled properly. (PQRY only)
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[ IX Troubleshooting ]
Check method and remedy
Confirm that the characteristic of capacity
drop due to piping length.
The piping pressure loss can be assumed
by temperature difference between the heat
exchanger inlet temperature (TH22) and
TH2 (Te). -> Change the pipe.
Refer to 1-1. (Compressor frequency does
not rise sufficiently.)Refer to the page on re-
frigerant amount adjustment
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). When
the temperature drops significantly, the for-
eign object may clog the pipe.
-> Remove the foreign object inside the
pipe.
Check the inlet air temperature and for short
cycling. Change the environment where the
indoor unit is used.
Check the discharge temperature to deter-
mine if the refrigerant leaks, as it rises if
there is a leak.
Refer to the section "Troubleshooting the
LEV."
It most likely happens when there is little dif-
ference or no difference between TH5 and
TH7.
Check the thermistor.
Check wiring.
Refer to the section "Troubleshooting the
LEV."
(9. [4] -6- ).
(1) Pressure sensor check
(2) Wiring check