Daikin RXSQ24TAVJU, Service Manual, Page: 62 / 311

Special Control SiUS331708EA
49 Functions and 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.
∗
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.
Outdoor unit
actuator
Electric symbol
Defrost preparation
operation
Defrost operation After defrost operation
24/36 class 48 class 60 class
Compressor M1C M1C M1C Upper limit control
→
0 rps
STEP 25 load (24/36 class)
STEP 21 load (48/60 class)
Increases 2 steps every 20
seconds from minimum
frequency until Pc – Pe >
0.4 MPa (58 psi) is achieved.
Outdoor fan M1F M1F
M1F,
M2F
Normal heating control
→
OFF
OFF STEP 8
Four way valve Y1S Y1S Y1S ON
→
OFF OFF ON
Main electronic
expansion valve
Y1E Y1E Y1E SH control
→
0 pulse 480 pulse (Fully open) 55 pulse
Subcooling
electronic
expansion valve
 
Y3E
Normal heating control
→
0 pulse
0 pulse 0 pulse
Hot gas bypass
valve
Y2S
 
OFF
→
ON OFF ON
→
OFF
Injection valve Y3S Y3S

OFF OFF OFF
Ending conditions
•
Up to 5 minutes 50
seconds
•
A lapse of 20 seconds
from four way valve
ON
→
OFF
•
16 minutes
•
Tb > 11°C (51.8°F)
•
Ts1 – Te < 5°C (9°F)
•
260 seconds
•
Pc > 2.7 MPa (391 psi)
•
Pc – Pe > 0.4 MPa
(58 psi)
OR
OR
&
OR
Indoor unit actuator Defrost operation
Indoor 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