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superheat and subcooling values after 5 minutes of run
time. See Table 6 for example of measuring superheat
and sub-cooling performance values. Superheat is to be
measured using suction temperature and pressure at the
compressor. Subcooling should be measured using the
liquid line temperature immediately outside the GT-S
cabinet and either the liquid line service valve pressure or
the compressor discharge pressure. Note that different
values of Table 6 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 will 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 1/2 turn to
open service port. Add vaporized R-22 (Gas) into the
suction side of the compressor until the pressure in the
system reaches approximately 60-70 psig. 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 five pounds per minute. Keep adding
refrigerant until the complete charge has been entered.
Superheat is to be measured using suction temperature
and pressure at the compressor. Subcooling should be
measured using the liquid line temperature immediately
outside the GT-S cabinet and either the liquid line service
valve pressure or the compressor discharge pressure.
Note that different values of Table 6 will be obtained due
to the pressure losses through the condenser heat
exchanger. Compare superheat and subcooling to the
values in Table 3. 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 will be measured. Proceed to
FINAL EVALUATION.
FINAL EVALUATION -In a split system, cooling sub-
cooling 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
Table 6. If unit runs satisfactorily then charging is
complete. If unit does not perform to specifications the
cooling txv (air coil side) may need to be readjusted until
the cooling superheat values are met.
To Check 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 in the suction line by
attaching refrigeration gauges to the schrader
connection on the side of the compressor.
3.
Convert the pressure obtained in Step 2 above to the
boiling point (sat temp) temperature by using the R-
22 Press/Temp 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 the boiling
point. Refer to the superheat Table 3 for superheat
ranges at specific entering water conditions.
Example:
The temperature of the suction line at the sensing bulb is
read at 50
°
F. The suction pressure at compressor is 65
psig which is the equivalent to 38
°
F saturation
temperature from R-22 Press/Temp conversion table on
the gauge set.
38
°
F subtracted from 50
°
F = 12
°
F Superheat
Determining Sub-Cooling:
1.
Measure the temperature of the liquid line on the
small refrigerant line (liquid line) just outside the
GT-S cabinet. This location will be adequate for
measurement in both modes unless a significant
temperature drop in the liquid line is anticipated.
2.
Determine the condensor pressure (High Side) by
attaching refrigerant gauges to the schrader connec-
tion on the liquid line service valve. If the hot gas
discharge line of the compressor is used, refer to the
apprpriate column in Table 3.
3.
Convert the pressure obtained in step 2 above to the
boiling point temperature by using the Press/Temp
conversion table on the gauge set.
4.
Subtract the temperature of Step 3 from the tempera-
ture of Step l . The difference will be the sub-cooling
value for that unit (total degrees below the boiling
point). Refer to the sub-cooling Table 3 for values at
specific entering water temperatures.
Example:
The condenser pressure at the service port is 225 prig
which is equivalent to 110
°
F and is 236psig at the
compressor (113
°
F)
100
°
F subtracted from 110
°
F = 10 degrees sub-cooling
13 degrees using the compressor discharge pressure.
