Mitsubishi Electric HP120TNU-A Service Handbook page 278

[8-9 Troubleshooting Problems with Major Components on BC Controller ]
1) BC controller: Phenomena when LEV is connected wrongly (reverse connection of LEV1 and LEV3 or LEV4) to the board.
Cooling-only
Non-cooling
SH12 small, SC11 small
SC16 small, branch pipe
SC small
BC controller sound
2) BC controller: Phenomena when LEV is connected wrongly (reverse connection of LEV3 and LEV4) to the board
Cooling-only
Non-cooling
SH12 large, SC11 small
SC16 small, branch pipe
SC small
3) Check method of fully open state or fully closed state of LEV
Check LEV opening (pulse) on the self-diagnosis LED (Outdoor control board SW1).
Full open: 3000 pulses
Fully closed: 41 pulses (In the case of heating-only mode, however, the pulse may become 41 or more.)
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.
When LEV is fully closed, check that there is no refrigerant flowing sound.
HWE18220_GB
Phenomena
Cooling-main
Non-cooling and non-heating
SH12 small, SC11 small
SC16 large, but branch pipe
SC small
BC controller sound PHM
large
Phenomena
Cooling-main
Non-cooling
SH12 large, SC11 small
SC16 small, branch pipe SC
small
Heating only
Indoor heating SC small Non-cooling
PHM large Indoor heating SC small
Heating only
SH12 large Non-cooling
SH12 large, SC16 small
Heating main
PHM large
Heating main
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chapter 8 -