IM 817-7
38 www.DaikinApplied.com
•
Insulate the suction line piping (minimum heat
.
•
Evacuate and properly charge the refrigerant system,
•
Charge to subcooling at the condensing unit per the
condensing unit manufacturer’s instructions, typically
15°F to 16°F at the unit ventilator, subcooling at
95ºF outdoor ambient (results in correct refrigerant
distribution at the coil to prevent low suction
temperatures)
•
Adjust TXV for correct superheat to eliminate/
•
Set superheat to 5°F to 7°F at the UV coil suction
line when 95°F outdoor ambient (proper system
superheat for optimum performance). Allow system
to settle for 20 to 30 minutes to reach stable steady
state conditions and then recheck/adjust superheat if
necessary, see
•
Compensate both subcooling and superheat for
actual outdoor ambient and indoor air temperatures
•
In windy areas, add wind baffles to condensing unit or
build a parapet (eliminate wind effect on condensing unit
coil for proper TXV refrigerant flow at lower ambient)
•
For lower ambient conditions install variable speed
condenser fan head pressure control to maintain
head pressures between 180psig and 280psig (for
proper TXV refrigerant flow at lower ambient), see
Figure 96: Insulate Bulb and Suction Line Piping
TXV (Thermal Expansion Valve)
Insulate Bulb, (Reacts
To Refrigerant Tempera-
ture and Not Ambient)
Insulate The Suction
Line Piping, (Minimum
Heat Pickup)
Return (Suction Line)
Supply (Liquid Line)
Pressure Taps (Field Installed)
Pressure Taps
(Field Installed)
Checking System Charge
The system charge should be checked under design
conditions [95°F outside air, 80°F/67°F (DB/WB) indoor
air]. Refer to condensing unit manufacturer’s guidelines.
Before adjusting refrigerant charge, verify that the unit
ventilator is operating at normal design cfm. Nominal cfm
is determined with a dry coil, and cfm will be reduced
during air conditioning operation with a wet coil. Filters
and coil must be clean and fan speed set at high.
temperature to obtain subcooling.
NOTICE
Typical conditions - 95ºF ambient, 75 psig suction, 285 psig head
pressure, 6-7ºF superheat, 15ºF subcooling.
Determining Subcooling
To determine correct subcooling:
1 .
Measure outdoor ambient. It must be between 65°F
and 105°F.
2 .
Measure liquid line temperature 6 inches from the
TXV inlet.
3 .
Measure liquid line pressure near the TXV.
4 .
Determine saturated liquid temperature from
saturated temperature pressure chart (
).
5 .
Subtract measured liquid line temperature from
saturated liquid temperature to obtain subcooling.
6 .
Adjust charge per condensing unit manufacturer
recommendation to obtain 15 - 16°F subcooling.
Table 31: Dimensions, DX Tubing inches (mm)
Models AVS, AVV,
AVB, AVR
Suction Line O .D .
Liquid Line O .D .
S07
3/4" (19mm)
1/4" (6mm)
S10
3/4" (19mm)
1/4" (6mm)
S13
7/8" (22mm)
3/8" (10mm)
S15
7/8" (22mm)
3/8" (10mm)
S20
7/8" (22mm)
3/8" (10mm)
piping dimensions are for systems with up to 30
ft. (9.14 m) vertical separation and up to 100 ft
(30.47 m)
horizontal separation from the outdoor condensing unit.
Figure 97: Typical Split System Evacuation/Charging Setup
Liquid
Line
Drier
Sight Glass
Suction Line Service Valve
Liquid Line Service Valve
Outdoor Fan
Compressor
Gauge Bar Hoses
Vacuum Pump
TXV
Indoor Fans
Charging
Cylinder
Indoor Coil
Outdoor Coil
Low Pressure
Gauge
Outdoor Condensing Unit
Unit Ventilator
High Pressure
Gauge
(By Others)
(By Others)
Pressure
Taps
(by others)