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charging the units to the correct subcooling for the various operat-
ing conditions. Accurate pressure gage and temperature sensing
device are required. Connect the pressure gage to the service port
on the liquid line service valve. Mount the temperature sensing de-
vice on the liquid line close to the liquid line service valve, and in-
sulate it so that outdoor ambient temperature does not affect the
reading. Indoor airflow must be within the unit's normal operating
range. Operate the unit for a minimum of 15 minutes. Ensure that
pressure and temperature readings have stabilized. Plot the liquid
pressure and temperature on chart and add or reduce the charge to
meet the curve. see Table 15. Adjust the charge to conform with
the charging chart, using the liquid pressure and temperature to
read the chart.
Table 15 — Using Plotted Operating Point
IF PLOTTED OPERATING
CONDITION IS
BELOW the curve
ABOVE the curve
38AUZ*25 CHECK COMPRESSOR OIL LEVEL
After adjusting the refrigerant charge, allow the unit to run fully
loaded for 20 minutes. Stop the compressors and check the oil lev-
el. Oil level should be 1/3 to 1/2 up on the sight glass (see Fig. 23).
60
54
48
42
36
30
24
18
12
-6
ADJUST CHARGE BY
REDUCE charge
ADD charge
15 Ton Charging Chart R-410A Refrigerant
140
120
Add Charge if
Above the Curve
100
80
60
6
40
0
20
50
100
150
200
350
700
1050 1400 1750 2100 2450 2800 3150 3500 3850
Pressure at Liquid Valve (PSIG / kPa)
Fig. 24 — 38AUZ*16 Charging Chart
1/2 (MAX)
1/3 (MIN)
Fig. 23 — Recommended Oil Level — 38AUZ*25
Add oil only if necessary to bring the oil into view in the sight
glass. If oil is added, run the circuit for an additional 10 minutes,
then stop and check oil level. If the level remains low, check the
piping system for proper design for oil return; also, check the sys-
tem for leaks. If checking the oil level with unit running in part
load, let unit run one hour, then run at full load for 10 minutes. If
oil does not return to acceptable sight glass levels, check for cor-
rect suction piping and line sizing.
FINAL CHECKS
Ensure that all safety controls are operating, control panel covers
are on, and the service panels are in place.
Remove Charge if
Below the Curve
250
300
350
400
450
22
500
550
600
38AU501082
C
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