Mitsubishi Electric City Multi PQHY-P72 Service Handbook page 289

[ IX Troubleshooting ]
Note1 BC controller: Phenomena when the pressure sensor is connected wrongly (reverse connection of P1 and P3) to the
board.
Cooling-only
Normal Non-cooling
Note2 Check the self-diagnosis switch (Heat source unit control board SW1).
Measurement data Symbol
Heat source unit
high pressure
Heat source unit
low pressure
BC controller pressure
(liquid side)
BC controller pressure
(intermediate part)
Note3 Check whether CNP1 (liquid side) connector on the BC controller control board and the connector CNP2 (intermedi-
ate part) are not disconnected or not loose.
Note4 Check the pressure value on the self-diagnosis switch (same as note1) with the connector of the applied pressure
sensor is disconnected from the board.
Cooling-main
Indoor heating SC small
SC11 large
Heating indoor Thermo ON
SC16 small
Especially noise is large.
PHM large
SW1 setting value
1 2 3 4 5 6 7 8 9 10
ON
63HS
1 2 3 4 5 6 7 8 9 10
ON
63LS
1 2 3 4 5 6 7 8 9 10
ON
P1
1 2 3 4 5 6 7 8 9 10
ON
P3
Symptoms
Heating only
SC11 large
SC16 small
PHM large
- 280 -
Heating main
Non-cooling
SC11 large
Indoor heating SC small
SC16 small
Heating indoor Thermo ON
PHM large
Especially noise is large.