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Special Control
SiUS28-902_B
20
Function
3.3
Defrosting Operation
Pc: High pressure sensor detection value
Pe: Low pressure sensor detection value
Tc: High pressure equivalent saturation temperature
Te: Suction pipe equivalent saturation temperature
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 exchanger (Tb)
Timer (2 hours at the minimum)
In addition, outdoor heat exchanger 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 1 minute to reduce noise on changing of the
four-way valve.
Outdoor unit actuator
Defrost preparation
operation
Defrost operation
Post Defrost operation
Compressor
52 Hz
177 Hz
2-step increase from
52 Hz to
(Pc – Pe > 58 psi)
every 20 seconds
Outdoor unit fan
STEP 8
OFF
STEP 8
Four-way valve
ON
OFF
ON
Main electronic expansion valve
(EV1)
SH control
1400 pls
200~400 pls
Hot gas bypass valve (SVP)
OFF
ON
ON
Receiver gas discharging valve
(SVG)
ON
ON
OFF
Ending conditions
130 seconds
15 minutes
Tb > 51.8
F
160 seconds
Pc – Pe > 58 psi
OR
OR
Indoor unit actuator
During defrost
Fan
Thermostat ON unit
OFF
Stopping unit
OFF
Thermostat OFF unit
OFF
Electronic expansion valve
Thermostat ON unit
500 pls
Stopping unit
500 pls
Thermostat OFF unit
500 pls