Defrost Control - Daikin SkyAir RZR-TA Series Service Manual

Special 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
 After 40 minutes have elapsed, defrost operation starts when the following items meet the
 Defrost operation starts every 2 hours, even if the reference values are not met.
Electric Symbol
Outdoor unit
18/24
actuator
class
Compressor M1C
Outdoor fan M1F
Main electronic Y1E
expansion valve
Subcooling —
electronic
expansion valve
Four way valve Y1S
Hot gas bypass Y2S
valve
Ending conditions
∗ 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.
Fan
Electronic expansion valve
114
operation.
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)
(A) Defrost preparation
30/36/42/48
control
class
M1C Upper limit control
M1F STEP 8
M2F
Y1E SH control
Y3E 0 pulse
Y1S ON
— OFF
2 minutes
Indoor unit actuator
Thermostat ON unit
Non-operating unit
Thermostat OFF unit
Thermostat ON unit
Non-operating unit
Thermostat OFF unit
(B) Defrost control
140 Hz Full load
OFF
480 pulse (Fully open)
0 pulse
OFF
ON
x 12 minutes
OR
x Tb > 11°C (51.8°F)
&
x Ts1 – Te < 5°C (9°F)

Defrost control

416 pulse
256 pulse
416 pulse
SiUS281811EA
(C) Control after defrost
Increases 2 steps every 20
seconds from minimum
frequency until Pc – Pe >
0.4 MPa (58 psi) is
achieved.
STEP 8
55 pulse
0 pulse
ON
ON
x 160 seconds
OR
x Pc – Pe > 0.4 MPa
(58 psi)
OFF
OFF
OFF
Part 4 Functions and Control