Daikin Sky Air R-407C, Service Manual, Page: 229 / 304

ESIE02–01 Overview of the heating mode functions
Part 2 – Functional Description 2–49
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3.9 Motor Operated Valve Control
Applicable units R(Y)P71-250B
Pump down
residual operation The unit conducts a pump down residual operation after each compressor stop command. The
purpose of this function is to collect the refrigerant in the liquid receiver in order to prevent refrigerant
from remaining in the indoor heat exchanger.
Start-up control When the compressor starts, a pump down operation is carried out in order to avoid liquid pumping.
The liquid receiver fills up and a minimum refrigerant amount is passed to the compressor. This
minimum refrigerant amount is required to avoid discharge pipe temperatures that are too high.
The opening degree of the expansion valve depends on the start-up number. If the first start-up fails,
the opening degree of the following start-up is adapted by the self-learning function.
Initial opening
degree The initial opening degree of the outdoor expansion valve depends on the indoor and outdoor air
temperature. The calculation of the opening degree is made at a thermostat ON and at the end of a
defrosting cycle.
Opening degree:
Self-learning
function When the system was stopped due to abnormal suction or discharge pressure, or due to a discharge
temperature that is too high, the expansion valve control tries to avoid the same breakdown. The
expansion valve increases the previous opening degree with 70 (in cooling mode) or 80 (in heating
mode) pulses at the next start-up.
There are maximum five start-up attempts. When the compressor stops again after the fifth start-up,
something is wrong with the unit and a unit check is necessary. The relevant error code appears on
the remote control.
Compressor
OFF
ON
EV
SV
Thermostat
Refrigerant
recuperation
0
480
OFF
ON
OFF
ON
Compressor
OFF
ON
EV
SV
Thermostat
1. Equalisation
2. Start-up control
3. Normal control
1 2 3
0
480
OFF
ON
OFF
ON