T h e Q u a l i t y L e a d e r i n C o n d i t i o n i n g A i r
R e s i d e n t i a l S p l i t - 6 0 H z R 4 1 0 A
R e v. : 0 3 A u g u s t , 2 0 1 2
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19
Refrigeration Installation
Turn service valves full out CCW (see Table 5) and then turn
back in one-half turn to open service ports. Add the required
refrigerant so that the total charge calculated for the unit
and line set is now in the system. Open the service valve
fully counter clockwise so that the stem will backseat and
prevent leakage through the schrader port while it is not in
use. Start unit in the heating mode and measure superheat
and subcooling values after 5 minutes of run time. See tables
14a to 15 for superheat and sub-cooling values. Superheat
is measured using suction temperature and pressure at the
compressor suction line. Subcooling should be measured
using the liquid line temperature immediately outside the
compressor section cabinet and either the liquid line service
valve pressure or the compressor discharge pressure. Note
that different values from tables 14a to 15 will be obtained due
to the pressure losses through the condenser heat exchanger.
Adding refrigerant will increase sub-cooling while superheat
should remain fairly constant allowing for a slight amount
of hunting in TXV systems. This increase in subcooling will
require 5 minutes or so of operation before it should be
measured. After values are measured, compare to the chart
and go to “FINAL EVALUATION.”
PARTIAL CHARGE METHOD
- Open service valve fully
counterclockwise and then turn back in one-half turn to open
service port. Add vaporized (Gas) into the suction side of
the compressor until the pressure in the system reaches
approximately 60-70 psig (R-22 systems) or 100-120 psig
(R-410A systems). Never add liquid refrigerant into the suction
side of a compressor. Start the unit in heating and add gas
to the suction port at a rate not to exceed
fi
ve pounds [2.27
kg] per minute. Keep adding refrigerant until the complete
charge has been entered. Superheat is measured using
suction temperature and pressure at the compressor suction
line. Subcooling should be measured using the liquid line
temperature immediately outside the compressor section
cabinet and either the liquid line service valve pressure or the
compressor discharge pressure. Note that different values
from tables 14a to 15 will be obtained due to the pressure
losses through the condenser heat exchanger. Adding
refrigerant will increase sub-cooling while superheat should
remain fairly constant allowing for a slight amount of hunting
in TXV systems. This increase in subcooling will require 5
minutes or so of operation before it should be measured. After
values are measured, compare to the chart and go to “FINAL
EVALUATION.”
FINAL EVALUATION
- In a split system, cooling subcooling values can be
misleading depending on the location of the measurement.
Therefore, it is recommended that charging be monitored in
the heating mode. Charge should be evaluated by monitoring
the subcooling in the heating mode. After initial check of
heating sub-cooling, shut off unit and allow to sit 3-5 minutes
until pressures equalize. Restart unit in the cooling mode
and check the cooling superheat against Tables 14a to 15. If
unit runs satisfactorily, charging is complete. If unit does not
perform to speci
fi
cations the cooling TXV (air coil side) may
need to be readjusted (if possible) until the cooling superheat
values are met.
Checking Superheat and Subcooling
Determining Superheat:
1. Measure the temperature of the suction line at a point
near the expansion valve bulb.
2. Determine the suction pressure by attaching refrigeration
gauges to the suction schrader connection at the
compressor.
3. Convert the pressure obtained in step 2 to saturation
temperature (boiling point) by using the pressure/
temperature conversion table on the gauge set.
4. Subtract the temperature obtained in step 3 from step 1.
The difference will be the superheat of the unit or the total
number of degrees above saturation temperature. Refer to
Tables 14a to 15 for superheat ranges at speci
fi
c entering
water conditions.
Determining Sub-Cooling:
1. Measure the temperature of the liquid line on the smaller
refrigerant line (liquid line) just outside of the cabinet. This
location will be adequate for measurement in both modes
unless a signi
fi
cant temperature drop in the liquid line is
anticipated.
2. Determine the condensor pressure (high side) by
attaching refrigerant gauges to the schrader connection
on the liquid line service valve. If the hot gas discharge
line of the compressor is used, refer to the appropriate
column in Tables 14a to 15.
3. Convert the pressure obtained in step 2 to the saturation
temperature by using the press/temp conversion table on
the gauge set.
4. Subtract the temperature of Step 3 from the temperature
of Step 1. The difference will be the sub-cooling value for
that unit (total degrees below the saturation temperature).
Refer to Tables 14a or 6b for sub-cooling values at
speci
fi
c entering water temperatures.
