41
After adding or removing charge the system
must be allowed to stabilize, typically 10-15
minutes,
before
making
any
other
adjustments.
The type of unit and options determine the
ranges for liquid sub-cooling and evaporator
superheat. Refer to the tables below when
determining the proper sub-cooling.
For units equipped with low ambient
(-17.78
°
C [0°F]) option see the special
charging instructions in the CF Series
Installation and Operation Manual.
Checking Liquid Sub-Cooling
Measure the temperature of the liquid line as
it leaves the condenser coil.
Read the gauge pressure at the liquid line
close to the point where the temperature was
taken. Use liquid line pressure as it will vary
from discharge pressure due to condenser
coil pressure drop.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the measured liquid line temperature
from the saturated temperature to determine
the liquid sub-cooling.
Compare calculated sub-cooling to the table
below for the appropriate unit type and
options.
Table 14 - Acceptable Refrigeration Circuit
Values
Notes:
1.
Must be charged with the hot gas valve closed.
After charging, operate the unit in reheat
(dehumidification) mode to check for correct
operation.
2.
The sub-cooling value in this table is for the unit
running in cooling mode of operation. If unit is a
heat pump, operate the unit in heating mode to
check for correct operation after charging in
cooling.
3.
The sub-cooling value in this table is for the unit
running in cooling mode of operation and the hot
gas valve closed. After charging, operate the unit
in reheat (dehumidification) mode to check for
correct operation and then in heating mode to
check for correct operation.
4.
Sub-cooling must be increased by 0.6
°
C (1°F) per
3.1 meters (10 feet) of vertical liquid line rise for
R-410A (AHU above CU). For example, a
cooling only unit with hot gas reheat and a vertical
liquid drop can charge to a sub-cooling value
between 2.8 and 8.3
°
C (5-15°F), but a cooling
only unit with hot gas reheat and a vertical liquid
rise of 9.1 m (30 ft) must charge to a sub-cooling
value of at least between 4.4 and 8.3
°
C (8-15°F).
DO
NOT
OVERCHARGE.
Refrigerant
overcharging leads to excess refrigerant in the
condenser coils resulting in elevated compressor
discharge pressure.
Cooling
Mode Liquid
Sub-Cooling
Values (
°
C)
Cooling
Mode Liquid
Sub-Cooling
Values (
°
F)
Cooling Only Unit
4
4.4 - 8.3
8-15
Cooling Only Unit
with Hot Gas Reheat
1,4
2.8 - 8.3
5-15
Heat PumpUnit
2,4
1.1 - 2.2
2-4
Heat Pump Unit with
Hot Gas Reheat
3,4
1.1 - 3.3
2-6
Cooling Only Unit
with LAC
4
4.4 - 8.3
8-15
Cooling Only Unit
with Hot Gas Reheat
& LAC
4
4.4 - 8.3
8-15
