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Fujitsu FO20R Series Installation Instructions Manual page 28

Variable speed r-410a heat pump outdoor units
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5.8.1 Measurement Device
1. With an R-410A gauge set, attach the high-
pressure hose to the access fitting on the liquid
line (small) service valve at the OD unit.
2. Attach the low-pressure hose to the exterior
suction port located between the two service
valves that is connected to the suction tube
between the reversing valve and compressor.
3. Attach a temperature probe within 6" [15.2 cm]
of the outside of the unit on the copper liquid line
(small line). For more accurate measurements,
clean the copper line prior to measurement and
use a calibrated clamp-on temperature probe or
an insulated surface thermocouple.
5.8.2 Preliminary Charging by
Adjust the system charge by
weight for the linear length of the refrigerant line set.
For a new installation, evacuation of inter-
connecting tubing and indoor coil is adequate;
otherwise, evacuate the entire system. Use the
factory charge shown in "Electrical and Physical
Data" in Section 3.2 of these instructions or on the
unit data plate. Note that the charge value includes
charge required for 15 ft. [4.6 m] of standard-size
liquid line without a filter drier.
Calculate actual charge required with the actual
installed liquid line size and length using:
1/4" [6.4 mm] O.D. = .3 oz./ft. [28.3 g/m]
5/16" [7.9 mm] O.D. = .4 oz./ft. [37.7 g/m]
3/8" [9.5 mm] O.D. = .6 oz./ft. [56.7 g/m]
1/2" [12.7 mm] O.D. = 1.2 oz./ft. [113.3 g/m]
Add 6 oz. for field-installed filter drier.
Charge Adjustment = (Line Set (oz./ft.) x Total
Length) – Factory Charge for Line Set
Example: A three ton heat pump unit with factory
installed 3/8" liquid service valve requires 75 ft. of
line set with a liquid line diameter of 1/2".
Factory Charge for Line Set = 15 ft. × .6 oz. = 9 oz.
Charge Adjustment = (1.2 oz. × 75 ft.) – 9 oz. =
+ 81 oz.
With an accurate scale (+/– 1 oz. [28.3 g]) or
volumetric charging device, adjust the refrigerant
charge based on the actual line set length. If the
entire system has been evacuated, add the total
calculated charge.
not always accurate since the application can
affect the optimum refrigerant charge. Charging by
weight is considered a starting point ONLY. Always
check the charge by using the Charging Chart
Charging by weight is
and adjust as necessary. CHARGING BY LIQUID
refrigerant of R-32 and R-125 (50/50). These
two refrigerants have different saturation curves
and therefore change state at different pressures
and temperatures. If charge is added to the
system in the vapor state, it is possible to have a
disproportionate amount of each part of the R-410A
blend which will cause unstable and inefficient
operation. Therefore, it is critical to add R-410A in
the liquid form only!
5.8.3 Preliminary Charging by
Pressures (Optional)
1. Following airflow verification and charge weigh-
in, run the unit for a minimum of 15 minutes
prior to noting pressures and temperatures.
measured at the indoor coil must be within 2°F
[1.1°C] of comfort conditions per the homeowner's
If the indoor temperature is above
or below this range, run the system to bring the
temperature down or run the electric heat/furnace to
bring the temperature up to within this range.
2. Note the Outdoor Dry Bulb Temperature,
ODDB° = _____°F [_____°C]. Unit charging
is recommended under the following outdoor
conditions ONLY:
Cooling Mode ONLY: 55°F [12.8°C] outdoor dry
bulb and above
Heating Mode ONLY: Between 40°F [4.4°C] and
60°F [15.6°C] outdoor dry bulb
3. Locate and note the design pressures. The
correct liquid and vapor pressures are found at
the intersection of the installed system and the
outdoor ambient temperature on the Charging
Chart located inside the access panel cover.
Liquid Pressure: = ______psig; Vapor Pressure
= ______psig
R-410A is a blended
Indoor conditions as



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