Si33-105 Outline of Control (Outdoor Unit) < Symbols using in this manual >
Function R407C PLUS Series Heat Recovery System 91
3.6.3 Defrost Control
Activates the defrosting operation to melt frost accumulated on the outdoor heat exchanger
during heating operation.
[Defrost start conditions]
When the following conditions are met during heating operation, the defrosting operation is
activated.
Tb : Distributor pipe temperature (°C) at heat exchanger outlet (in cooling operation)
Ta : Outside temperature (°C)
When the above conditions are met, the following “defrosting operation preparation” operation is
conducted for 2 minutes, then the defrosting operation is activated.
1. Outputs “oil return, defrost preparation” signal to indoor units.
2. Turns on the liquid injection solenoid valve (SVT) based on Td or DSH.
Td : Discharge pipe temperature
DSH : Discharge super heat temp.
"
Liquid injection : Refer to page 77.
Note: Note.1
When compressor stops operation at outdoor temperature >1°C, reset cumulating timer.
OR
&
When cumulative compressor operating time from power On or completion of
previous defrosting operation exceeds 30 minutes Note.1
When condition (Tb ≤ X × Ta – A) remains for 5 minutes (–25 ≤ Tb ≤ –10)
(Value of A based on the following table. When Ta ≥ 7, Ta = 7°C is used in calculation)
When forced defrost setting (local setting) is turned on and Tb < 12.5°C
Defrost setting
Defrost change
setting
X
LMH
No-setting (Factory set) A=12 A=14 A=16
Outside air Ta > 0°C 0.6
Outside air Ta
≤
0°C
0.8
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