Si18-525B Special Control
Function 117
3.3 Defrosting Operation
The defrost operation is performed to solve frost on the outdoor unit heat exchanger when
heating, and the heating capacity is recovered.
[Conditions to start]
The defrost operation is started referring following conditions.
Outdoor heat exchanger heat transfer co-efficiency
Temperature of heat-exchange (Tb)
Low pressure equivalent saturation temperature (Te)
Timer (2 hours at the minimum)
In addition, outdoor heat-exchange co-efficiency is derived from Tc, Te, and the compressor
load.
* From the preparing operation to the defrost operation, and from the defrost operation to the
operation after defrost, the compressor stops for 110 sec. to reduce noise on changing of the
four way valve.
Outdoor unit actuator
Defrost preparation
operation
Defrost operation Post Defrost operation
Compressor Upper limit control 140 Hz
2-step increase from
52 Hz to
(Pc - Pe>0.4 MPa)
every 20 sec.
Outdoor unit fan STEP8 OFF STEP8
Four way valve ON OFF ON
Main electronic expansion valve
(EV1)
SH control 2000 pls 200~400 pls
Subcooling electronic expansion
valve (EV2)
0 pls 0 pls 0 pls
Hot gas bypass valve (SVP) OFF ON ON
Receiver gas discharging valve
(SVG)
ON → OFF ON → OFF ON → OFF
Ending conditions 130 sec.
• Max. 18 min.
• Tb >11°C
• 160 sec.
• Pc - Pe>0.4MPa
or
or
Indoor actuator During defrost
Indoor unit fan
Thermostat ON unit OFF
Stopping unit OFF
Thermostat OFF unit OFF
BP unit electronic expansion
valve
Thermostat ON unit SH control
Stopping unit 80 pls
Thermostat OFF unit SH control
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