Mitsubishi Electric City Multi PQHY-P72 Service Handbook page 293

[ IX Troubleshooting ]
Note1 BC controller: Phenomena when LEV is connected wrongly (reverse connection of LEV1 and LEV3) to the board.
Cooling-only
Non-cooling
SH12 small, SC11 small
SH16 small, branch pipe
SC small
BC controller sound
Note2 Check method of fully open state or fully closed state of LEV
1) Check LEV opening (pulse) on the self-diagnosis LED (Heat source unit control board SW1).
Full open: 2000 pulses
Fully closed: 110 pulses (In the case of heating-only mode, however, the pulse may become 110 or more.)
2) When LEV is fully open, measure the temperature at the upstream and downstream pipes of LEV, and make
sure that there is no temperature difference.
3) When LEV is fully closed, check that there is no refrigerant flowing sound.
Note3 Refer to the chart below to judge LEV opening controlled by the values of the differential pressure and of the super-
heat. (BC controller LEV basic operation characteristic)
NU-
G,GA
(Main)
NU-GB
LEV3a
(Sub)
Cooling-main
Non-cooling and non-heat-
ing
SH12 small, SC11 small
SH16 large, but branch
pipe SC small
BC controller sound
large
Malfunction Operation
Part
mode mode
Inclined to
Heating only
close
Heating-
LEV1
Cooling-
Inclined to
open
Cooling-only
Cooling-
Inclined to
close
Heating only
Heating-
LEV3
Cooling-only
Cooling-
Inclined to
open
Heating only
Heating-
Cooling-only
Inclined to
Cooling-
close
Cooling-only
Inclined to
Cooling-
open
Phenomena
Heating only
Indoor heating SC small
PHM large
PHM
Content
Difference between high
pressure (P1) and interme-
diate pressure (P3) is large.
main
Difference between high
pressure (P1) and interme-
main
diate pressure (P3) is
small.
SH12 is large.
main
Difference between high
pressure (P1) and interme-
diate pressure (P3) is
main
small.
SC16 and SH12 are small.
main
Difference between high
pressure (P1) and interme-
main diate pressure (P3) is large.
SH22 is large.
main
SH22 is small.
main
- 284 -
Heating main
Non-cooling
Indoor heating SC small
PHM large
Standards of judgment on
unit stable operation
0.3 - 0.4MPa
[44 - 58psi]
SH12 < 20K [36°F]
0.3 - 0.4MPa
[44 - 58psi]
SC16 > 3K [5°F]
SH12 > 3K [5°F]
0.3 - 0.4MPa
[44 - 58psi]
SH22 < 20K [36°F]
SH22 > 3K [5°F]