5. Measure liquid refrigerant pressure at the service valve by
attaching an accurate pressure gauge to the service port
and record the pressure.
NOTE: When only the lead compressor is running, the
suction pressure will be higher than a standard
single speed system, or a dual compressor sys-
tem with both compressors running. This is a
normal operation for a dual compressor system
operating with a large indoor coil at part load
capacities.
6. Refer to the Table 3 to find the recommended subcooling
temperature.
7. Refer to Table 4 to determine the proper liquid line tempera-
ture at the point where the "Required Subcooling Tempera-
ture" and "Measured Liquid Pressure"(from step 5)
intersect. Record the required liquid line temperature.
8. Measure the liquid line temperature by attaching an accu-
rate electronic thermometer or a thermistor at the liquid line
near the condensing unit.
9. If the liquid line temperature is higher than the value deter-
mined in step 7, add refrigerant charge carefully until the
recommended subcooling temperature is obtained at the
corresponding liquid line pressure.
CAUTION: D O N O T OV ER C H AR GE TH E S Y ST EM ,
THIS COULD LEAD TO DAMAGE TO THE
COMPRESSORS.
It is suggested to maintain the recommended subcooling
levels indicated in Table 4, within
±
2
°
F. Too low a subcool-
ing or too high a subcooling will result in poor performance
of the air conditioning unit.
NOTE: If liquid line temperature is lower, remove and
recover the refrigerant charge until the recommended sub-
cooling temperature is obtained.
EXAMPLE:
Given an H1DS036 with only the lead compressor operating
on first stage.
1. Liquid pressure at the service valve = 179 lbs.
2. Recommended subcooling temperature from Table 3.
= 10
°
F
3. Required liquid line temperature from Table 4 = 84
°
F
If the measured liquid line temperature at the liquid line near
the condensing unit = 89
°
F, then the actual level of subcooling
based on Table 4 = 5
°
F
Therefore, add charge to reach required liquid line tempera-
ture given in Step 3, thereby, reaching the recommended
subcooling level in Step 2 above.
If the measured liquid line temperature at the liquid line near
the condensing unit = 79
°
F, then the actual level of subcooling
based on Table 4 = 15
°
F.
Therefore, remove and recover charge to reach required liquid
line temperature given in Step 3, thereby, reaching the recom-
mended subcooling level in Step 2.
Once the charge is established when the lead compressor is
running, it is not necessary to establish the charge once again
when both compressors are running. However it is recom-
mended to energize the second compressor to verify system
performance.
APPROVED SYSTEM COMBINATIONS
(Outdoor Unit / Variable Speed Air Handler & Coil)
CONDENSING UNIT
FACTORY CHARGE
LBS. - OZ.
INDOOR COIL
ADJUSTMENT
CHARGE, OZ.
H1DS036
N1VSD14
G3HC / G1FC036
9 - 9
+0
G3HC / G1FC042
+0
N2VSD20
G3HC / G1FC048
+0
G3HC / G1FC060
+14
H1DS048
N2VSD20
G3HC / G1FC048
9 - 9
+0
G3HC / G1FC060
+14
H1DS060
N2VSD20
G3HC / G1FC060
14 - 6
+0
TABLE 5 - CHARGE ADD STANDARD COILS
UNIT
SIZE
LIQUID LINE OD
VAPOR
LINE OD
R22 CHARGE
OZ / FT
036, 048, 060
3/8
7/8
0.70
TABLE 6 - REFRIGERANT LINE CHARGES
550.37-N1Y
10
Central Environmental Systems
