Defrost Operation - Daikin RXSQ24TAVJU Service Manual

Special Control
3.3

Defrost Operation

Pc : High pressure sensor detection value
Pe : Low pressure sensor detection value
Tc : High pressure equivalent saturation temperature
Te : Low pressure equivalent saturation temperature
Ts1 : Suction pipe temperature detected by thermistor R3T (suction pipe 1)
Tb : Heat exchanger temperature
Defrost operation is performed to melt frost on the outdoor heat exchanger when heating, and thus recover
heating capacity.
Starting conditions
Defrost operation is started referring to the following conditions.
• Outdoor heat exchanger heat transfer coefficiency
• Timer setting (Two hours at the minimum)
In addition, outdoor heat exchanger coefficiency is derived from Tc, Te, and compressor load.
Electric symbol
Outdoor unit
actuator
24/36 class 48 class 60 class
Compressor M1C
Outdoor fan M1F
Four way valve Y1S
Main electronic
Y1E
expansion valve
Subcooling

electronic
expansion valve
Hot gas bypass
Y2S
valve
Injection valve Y3S
Ending conditions
∗ From the preparation 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.
Indoor fan
Electronic expansion valve
49
Defrost preparation
operation
M1C Upper limit control → 0 rps
M1C
Normal heating control →
M1F,
M1F
M2F OFF
ON → OFF
Y1S Y1S
SH control → 0 pulse
Y1E Y1E
Normal heating control →

Y3E
0 pulse
  OFF → ON

Y3S OFF
• Up to 5 minutes 50
seconds
• A lapse of 20 seconds
OR
from four way valve
ON → OFF
Indoor unit actuator
Thermostat ON unit
Non-operating unit
Thermostat OFF unit
Thermostat ON unit
Non-operating unit
Thermostat OFF unit
Defrost operation
STEP 25 load (24/36 class)
STEP 21 load (48/60 class)
OFF
OFF
480 pulse (Fully open)
0 pulse
OFF
OFF
• 16 minutes
• Tb > 11°C (51.8°F)
OR &
• Ts1 – Te < 5°C (9°F)
Defrost operation
SiUS331708EA
After defrost operation
Increases 2 steps every 20
seconds from minimum
frequency until Pc – Pe >
0.4 MPa (58 psi) is achieved.
STEP 8
ON
55 pulse
0 pulse
ON → OFF
OFF
• 260 seconds
• Pc > 2.7 MPa (391 psi)
OR
• Pc – Pe > 0.4 MPa
(58 psi)
OFF
OFF
OFF
416 pulse
256 pulse
416 pulse
Functions and Control