Defrost Operation - Daikin VRV IV-S RXTQ-TAVJU Series 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 suction 1 thermistor
Tb : Heat exchanger temperature
Defrost operation is performed to melt frost on the outdoor unit 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 co-efficiency
• Timer setting (Two hours at the minimum)
In addition, outdoor heat-exchange co-efficiency is derived from Tc, Te, and compressor load.
Electric symbol
Outdoor unit
RXTQ36
actuator
TAVJU
Compressor M1C M1C M1C Upper limit control
Outdoor fan M1F
Four way valve Y1S
Main electronic
Y1E
expansion valve
Subcooling

electronic
expansion valve
Hot gas bypass
Y2S
valve
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
41
Defrost preparation
RXTQ48 RXTQ60
operation
TAVJU TAVJU
M1F M1F,
STEP 8
M2F
Y1S Y1S ON
Y1E Y1E SH control

Y3E 0 pulse
 
OFF
2 minutes
Indoor unit actuator
Thermostat ON unit
Stopping unit
Thermostat OFF unit
Thermostat ON unit
Stopping unit
Thermostat OFF unit

Defrost operation

140 Hz Full load
OFF
OFF
480 pulse (Fully open)
0 pulse
ON
• 12 minutes
OR
• Tb > 11°C (51.8°F)
&
• Ts1 – Te < 5°C (9°F)
Defrost operation
SiUS331604E
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
• 160 seconds
OR
• Pc – Pe > 0.4 MPa
(58 psi)
OFF
OFF
OFF
416 pulse
256 pulse
416 pulse
Functions and Control