Daikin SkyAir FHQ24PVJU - Defrost Control

Special Control SiUS281811EA
114 Part 4 Functions and Control
3.3 Defrost Control
Pc: High pressure sensor detection value
Pe: Low pressure sensor detection value
Tb: Heat exchanger deicer temperature
Tc: High pressure equivalent saturation temperature
Te: Low pressure equivalent saturation temperature
Ts1: Suction pipe temperature detected by thermistor R3T
Defrost control is performed to melt frost on the outdoor heat exchanger when heating, and thus
recover heating capacity.
Starting conditions
 Defrost operation is not conducted before 40 minutes have elapsed from the start of heating
operation.
 After 40 minutes have elapsed, defrost operation starts when the following items meet the
reference values.
 Heat transfer coefficient of the outdoor heat exchanger (The heat transfer coefficient of the
outdoor heat exchanger is computed from Tc, Te, and compressor loads.)
 Outdoor heat exchanger deicer temperature (Tb)
 Defrost operation starts every 2 hours, even if the reference values are not met.
∗ Between (A) defrost preparation control and (B) defrost control, and between (B) defrost control
and (C) control after defrost, the compressor stops for 1 minute to reduce noise on changing of the
four way valve.
Outdoor unit
actuator
Electric Symbol
(A) Defrost preparation
control
(B) Defrost control (C) Control after defrost
18/24
class
30/36/42/48
class
Compressor M1C M1C Upper limit control 140 Hz Full load Increases 2 steps every 20
seconds from minimum
frequency until Pc – Pe >
0.4 MPa (58 psi) is
achieved.
Outdoor fan M1F M1F
M2F
STEP 8 OFF STEP 8
Main electronic
expansion valve
Y1E Y1E SH control 480 pulse (Fully open) 55 pulse
Subcooling
electronic
expansion valve
— Y3E 0 pulse 0 pulse 0 pulse
Four way valve Y1S Y1S ON OFF ON
Hot gas bypass
valve
Y2S — OFF ON ON
Ending conditions 2 minutes
x 12 minutes
x
Tb > 11°C (51.8°F)
x Ts1 – Te < 5°C (9°F)
OR
&
x 160 seconds
x
Pc – Pe > 0.4 MPa
(58 psi)
OR
Indoor unit actuator Defrost control
Fan
Thermostat ON unit OFF
Non-operating unit OFF
Thermostat OFF unit OFF
Electronic expansion valve
Thermostat ON unit 416 pulse
Non-operating unit 256 pulse
Thermostat OFF unit 416 pulse