Daikin BPMK928B42, Service Manual

Page: 174 / 410

Si18-201 System control
Main Functions 161
3.32 Heat Exchanger Isothermal Control in Heating Operation
Purpose of the
Function This function ensures appropriate refrigerant distribution when room units are operating in the
heating mode.
It prevents abnormal increase of the high pressure and operation with gas shortage due to
uneven refrigerant distribution (Protection function).
Outline The indoor unit heat exchanger thermistors (of all connected room units including non-operating
room units) in heating operation are detected. Then, the highest heat exchanger temperature
DCMXT is compared with the heat exchanger temperature of each room unit. If the
temperature difference exceeds the predetermined value, it is judged that that indoor unit heat
exchanger thermistor position in subcooled zone, and the motorized valves of room units with
the temperature difference exceeding the predetermined level is opened to return to the
saturation zone.
Since this is a protection function, it is effective for all connected room units in heating operation
excluding those in defrosting operation. This function is inactive in room units with transmission
problems.
Details The heat exchanger temperature is detected at every sampling time of 20 sec of the heat
exchanger isothermal control, and maximum value DCMXT of each heat exchanger
temperature is obtained.
If the temperature difference between the heat exchanger temperature and maximum heat
exchanger temperature value exceeds 10°C, it is judged that the heat exchanger intermediate is
in the subcooled zone, and the motorized valve is opened.