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14.4 Subcooling Charging Below 55º F Outdoor Temp. (In Heating Only)
The Subcooling Charging method in cooling is not recommended below 55º F outdoor temperature.
The recommended method of charging at outdoor temperatures below 55º F is weighing in the charge. Return
when weather conditions permit charge verification through subcooling.
STEP 1 - Determine additional charge.
Note: The nameplate charge value represents the amount of refrigerant shipped in the outdoor unit and is com-
patible with 10 feet of AHRI rated refrigerant lines and the smallest AHRI rated coil.
Using the method below, find the charge associated with the additional length of tubing above 10 ft. and record
it below.
Weigh-In Method can be used for the initial installation, or anytime a system charge is being replaced. Weigh-In
Method can also be used when power is not available to the equipment site or operating conditions (indoor/out-
door temperatures) are not in range to verify with the subcooling charging method.
Calculating Charge Using the Weigh-In Method
STEP 1 - Measure in feet the distance between
the outdoor unit and the indoor unit and record on
Line 1.Include the entire length of the line from
the service valve to the IDU.
STEP 2 - Enter the charge multiplier (0.47 oz./ft for
3/8" and 0.30 oz./ft for 5/16"). Each linear foot of
interconnecting tubing requires the addition of
0.6 oz of refrigerant.
STEP 3 - Multiply the total length of refrigerant
tubing (Line 1) times the value on Step 2.
Record the result on Line 3 of the Worksheet.
STEP 4 - This is the amount of refrigerant to
weigh-in prior to opening the service valves.
.
STEP 2 - Stabilize the system by operating for a
minimum of 20 minutes.
At startup, or whenever charge is removed or added,
the system must be operated for a minimum of 20
minutes to stabilize before accurate measurements
can be made.
STEP 3 - Check the liquid line temperature and liquid gage pressure to obtain a minimum of 10º subcooling in
heating mode.
Measured Liquid Line Temp = __________ º F
Liquid Gage Pressure = __________ PSIG
STEP 4 - Add charge if a minimum of 10º subcooling is not obtained with the namplate charge plus additional
charge previously added.
18-BC117D1-1B-EN
1. Line length (ft)
2. Charge multiplier
3. Step 1 x Step 2
4. Refrigerant
20 MIN.
= ______________
=
for 3/8", use 0.47 oz.
per foot and for 5/16",
use 0.30 oz. per foot
= _____________
= _____________
17
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