Service Manual

SiUS181631EA Special Control
Functions and Control 59
3.3 Defrosting Operation
The defrosting operation is performed to solve frost on the outdoor unit heat exchanger when
heating, in order to recover heating capacity.
Conditions to start
The defrosting operation is started referring to the following conditions:

Outdoor heat exchanger heat transfer co-efficiency

Outdoor heat exchanger temperature (Tb)

Timer (2 hours at the minimum)
Outdoor heat-exchange co-efficiency is derived from Tc, Te, and the compressor load.
∗
From the preparation to the defrost operation, and from the defrost operation to the post defrost
operation, the compressor stops for 1 minute to reduce noise on changing of the four way valve.
3.4 Pump-down Residual Operation
Outline When activating the compressor, if there is liquid refrigerant remaining in the heat exchanger, the
liquid refrigerant enters into the compressor and dilutes the oil inside resulting in a decrease of
lubricity. Therefore, the pump-down residual operation is performed to collect the refrigerant in the
heat exchanger when the compressor is down.
Outdoor unit actuator
Defrost preparation
operation
Defrost operation Post defrost operation
Compressor Upper limit control 140 Hz Full load
36 Hz Unload
+2 steps / 20 sec.
(until Pc - Pe > 0.4 MPa)
(134 ftAq)
Outdoor fan STEP 8 OFF STEP 8
Four way valve (Y1S) ON OFF ON
Main electronic expansion valve (Y1E) SH control 480 pulse 55 pulse
Subcooling electronic expansion valve
(Y3E)
0 pulse 0 pulse 0 pulse
Hot gas bypass solenoid valve (Y2S) OFF ON ON
Ending conditions 2 min.
•
15 min.
•
Tb > 11°C
(51.8°F)
•
Ts1 – Te < 5°C
(9°F)
•
160 sec.
•
Pc – Pe > 0.4 MPa
(134 ftAq)
or
&
or
Indoor unit actuator Operation
Indoor fan
Thermostat ON unit OFF
Stopping unit OFF
Thermostat OFF unit OFF
Electronic expansion valve of
BP unit
Thermostat ON unit SH control
Stopping unit 80 pulse
Thermostat OFF unit SH control