39
Before Charging
Refer to the Unit Nameplate to determine
which refrigerant must be used to charge the
system.
Unit being charged must be at or near full
load conditions before adjusting the charge.
Units equipped with hot gas bypass must
have the hot gas bypass valve closed to get
the proper charge.
Units equipped with hot gas reheat must be
charged with the hot gas reheat valves closed
while the unit is in cooling mode to get the
proper charge. After charging, operate the
unit in reheat (dehumidification) mode to
check for correct operation.
Units equipped with heat pump options must
be charged in cooling mode to get the proper
charge. After charging, operate the unit in
heating mode to check for correct charge.
Charge may need to be adjusted for heating
mode. If adjustments are made in the heating
mode, cooling mode must be rerun to verify
proper operation.
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.
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
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. 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
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