Defrost Cycle; Indoor Coil Freeze Prevention - Daikin FTXN25L Service Manual

2.16.4 PI Control
P control: ∆ T of each indoor is calculated at every sampling time of 20s and compressor rotation is adjusted
according to the difference from the previously calculated rotation.
I control: if the operating frequency is not changed more than a certain fixed time:
• If Σ∆T is small : lower frequency.
• If Σ∆T is large : increase frequency.
2.16.5 Limit Rotation
Determine from
• Upper limit rotation
A minimum value was determined among the upper limits rotation, i.e. protection controls.
• Lower limit rotation
A maximum value was determined among the lower limits rotation, i.e. protection controls.
Generally, compressor rotation is controlled within 5 zones: stop, drop, keep, up and reset subjected to a
particular operating temperature/current/pressure.
Zone
Stop
Drop
Keep
Up
Reset

2.17 Defrost Cycle

During defrost
Compressor
4-way valve
EXV in operation room
Outdoor fan
Indoor fan
Condition for entering defrost
• Compressor minimum run time – 6 minutes OR
• Compressor accumulated run time of 45 minutes if Outdoor coil < 3°C.
Condition for terminating defrost
• Outdoor coil > 12°C or
• Total defrost timer of 650 seconds.

2.18 Indoor Coil Freeze Prevention

Only available in cooling mode.
When the indoor coil temperature < 2°C, the compressor starts to drop the frequency.
This protection will cut in when:
• Indoor coil temperature < 0°C for more than 180s. Compressor will stop, outdoor fan stop after 30s and
indoor fan can only run at lowest fan speed.
The unit can only be restarted after 3 minutes.
When the indoor coil temperature > 13°C, the compressor frequency will be reset based on the outdoor
ambient, room and set temperature.
Control
Compressor is stopped when a certain limit reaches the stop zone for abnormality
correction.
Frequency will be dropped with a timer setting.
Frequency is maintained at lower/upper limit.
Frequency will be increased with a timer setting.
Frequency lower/upper limit is canceled and returned to command rotation.
All models
ON
OFF
Fixed opening
OFF
OFF
Algorithm & Control
26